Class 9

JAC Class 9 Science Notes in Hindi & English Jharkhand Board

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JAC Jharkhand Board Class 9th Science Notes in Hindi & English Medium

JAC Board Class 9th Science Notes in English Medium

JAC Board Class 9th Science Notes in Hindi Medium

JAC Class 9 Science Important Questions and Answers in Hindi & English Jharkhand Board

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JAC Jharkhand Board Class 9th Science Important Questions in Hindi & English Medium

JAC Board Class 9th Science Important Questions in English Medium

JAC Board Class 9th Science Important Questions in Hindi Medium

JAC Class 9 Science Solutions in Hindi & English Jharkhand Board

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JAC Jharkhand Board Class 9th Science Solutions in Hindi & English Medium

JAC Board Class 9th Science Solutions in English Medium

JAC Board Class 9th Science Solutions in Hindi Medium

JAC Class 9th Science Solutions Chapter 14 Natural Resources

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JAC Board Class 9th Science Solutions Chapter 14 Natural Resources

JAC Class 9th Science Natural Resources InText Questions and Answers

Page 193

Question 1.
How is our atmosphere different from the atmospheres on Venus and Mars?
Answer:
Our atmosphere contains gases like nitrogen, oxygen, carbon dioxide, water vapour and other gases in very small amounts. Atmospheres of Venus and Mars have about 95% of carbon dioxide. So, life is not possible there.

Question 2.
How does the atmosphere act as a blanket?
Answer:
The atmosphere acts as a blanket by performing the following functions:

  1. It keeps the average temperature of the earth fairly constant during day time and even during the course of whole year. .
  2. It prevents a sudden increase in the temperature during day time.
  3. It slows down the escape of heat from the surface of the earth into outer space during night time.

Question 3.
What causes winds?
Answer:
An uneven heating of the earth’s surface causes winds. On being heated, air becomes lighter and rises up. As a result, a region of low pressure is created. Then, air from a high pressure region moves to the low pressure region, causing wind.

JAC Class 9th Science Solutions Chapter 14 Natural Resources

Question 4.
How are clouds formed?
Answer:
During daytime, on being heated, a large amount of water evaporates from various water bodies and goes into the air. A part of this water vapour also reaches the atmosphere through biological activities. This causes the air in the atmosphere to heat up. When this heated air rises, it expands and cools, which results in the condensation of water vapour forming water droplets. The presence of dust and other suspended particles in air also facilitates the process of condensation. The formation of water droplets leads to the formation of clouds.

Question 5.
List any three human activities that you think would lead to air pollution.
Answer:
Three human activities which lead to air pollution are:
(a) Burning of fuels like coal, petroleum, kerosene.
(b) Smoke released from industries.
(c) Emissions from vehicles.

Page 194

Question 1.
Why do organisms need water?
Answer:
Organisms need water for the following activities:
(a) All cellular processes occur inside water.
(b) Transportation of substances in our body takes place by dissolving in water.
(c) Terrestrial animals require water for getting rid of wastes from their body.
(d) Plants require water for photosynthesis.

Question 2.
What is the major source of fresh water in the city/town/village where you live?
Answer:
The major sources of water are:
(a) Water in the form of snow, ice – covered mountains
(b) Underground water in well
(c) Surface water like in lakes, rivers, ponds
(d) Rainfall
(e) Stored rainwater in tanks, dams

Question 3.
Do you know of any activity which may be polluting this water source?
Answer:
Yes, the water is polluted by sewage, dumping waste in river, factory waste, etc.

Page 196

Question 1.
How is soil formed?
Answer:
Soil is formed by breaking down of rocks at or near the surface of the earth through various physical, chemical and biological processes by various factors such as the sun, water, wind and living organisms.
1. Sun: During day time, the rocks get heated up. This causes the rocks to expand. During night time, these rocks cool down and contract. However, all parts of the rocks do not undergo expansion and contraction at the same rate. This causes the formation of cracks and breaking up of huge rocks into smaller pieces.

2. Water: Water catalyses the process of formation of soil in two ways:

  • Water goes into the cracks and crevices formed in the rocks. When this water freezes, its volume increases. As a result, the size of the cracks also increases. This helps in the weathering of rocks.
  • Running water wears away hard rocks over long periods of time. Water moving in fast speed carries big and small particles of rocks downstream. These rocks rub against each other, resulting in breaking down of rocks. These smaller particles are carried away by running water and deposited down its path.

3. Wind: Strong winds carry away rocks, which causes rubbing of rocks. This results in the breaking down of rocks into smaller and smaller particles.

4. Living organisms: Some living organisms like lichens help in the formation of soil. Lichens also grow on rocks. During their growth, lichens release certain substances, which cause the rock surface to powder down forming a thin layer of soil. On this thin layer of soil, some small plants like moss also grow. They further cause the breaking down of the rock particles with the growth of their roots.

Question 2.
What is soil erosion?
Answer:
The removal of fertile topsoil by air, wind or water is called soil erosion.

Question 3.
What are the methods of preventing or reducing soil erosion?
Answer:
The following are some methods which can prevent or reduce soil erosion:

  1. Soil should have some vegetation, like grass, growing on it, so that it does not get carried away by rainwater or wind.
  2. Afforestation or planting of trees, so that roots hold the soil and prevent soil erosion.
  3. Overgrazing should be avoided.

Page 201

Question 1.
What are the different states in which water is found during the water cycle?
Answer:
Various states in which water is found during the water cycle are:

  1. Water in liquid state: present in various sources like lakes, rivers, underground water, etc.
  2. Water vapour (gaseous state): Water evaporates from water bodies and due to transpiration by plants.
  3. Clouds: Condensed water vapour is present in clouds.
  4. Water as rain is in liquid state while that as snowfall is in solid state.

Question 2.
Name two biologically important compounds that contain both oxygen and nitrogen?
Answer:
Two biologically important compounds that contain both oxygen and nitrogen are:

  • Amino acids
  • Deoxyribonucleic acid (DNA)

Question 3.
List any three human activities which would lead to an increase in the carbon dioxide content of air.
Answer:
The following activities of human beings may increase carbon dioxide content of air:
(a) Burning of fuels in various processes like heating, cooking, transportation and industries.
(b) Human induced forest fires.
(c) The process of deforestation, i.e., the cutting down of trees. This decreases the uptake of carbon dioxide for photosynthesis. Eventually, the content of carbon dioxide increases.

JAC Class 9th Science Solutions Chapter 14 Natural Resources

Question 4.
What is the greenhouse effect?
Answer:
Some gases like carbon dioxide, methane and nitrous oxide prevent the escape of heat from the earth’s surface by trapping it. This increases the average temperature of the earth. This is called the greenhouse effect.

Question 5.
What are the two forms of oxygen found in the atmosphere?
Answer:
Oxygen is present in free form like O2 (oxygen molecule), ozone (O3) and combined form like oxides of metals and non-metals, e.g., CO2, NO2, SO2, H2O, etc.

JAC Class 9th Science Natural Resources Textbook Questions and Answers

Question 1.
Why is the atmosphere essential for life?
Answer:
Atmosphere is very important for sustaining life:

  1. It contains various gases like O2, CO2, N2 which are required for various life processes by plants and animals.
  2. CO2 gas is used by plants to prepare food by the process called photosynthesis
  3. Oxygen is required for burning, combustion and for respiration.
  4. Ozone layer is acting as a protective layer, which prevents the harmful U.V. rays to enter the earth’s atmosphere.
  5. C2 dissolved in water forms carbonates which are required by the animals to form shells.

Question 2.
Why is water essential for life?
Answer:
Water is essential for life because of the following reasons:

  1. All life processes that take place in the cells require water medium.
  2. Water is needed for transportation of various substances from one part of the body to the other in dissolved form.
  3. All reactions taking place within our body and within the cells occur between substances that are dissolved in water.
  4. Terrestrial life – forms require fresh water for the transportation of substances and also to get rid of high amounts of wastes.

Question 3.
How are living organisms dependent on the soil? Are organisms that live in water totally independent of soil as a resource?
Answer:
All living organisms are directly or indirectly dependent on soil. dissolved in water forms carbonates which are required by the animals to form shells.

Question 2.
Why is water essential for life?
Answer:
Water is essential for life because of the following reasons:

  1. All life processes that take place in the cells require water medium.
  2. Water is needed for transportation of various substances from one part of the body to the other in dissolved form.
  3. All reactions taking place within our body and within the cells occur between substances that are dissolved in water.
  4. Terrestrial life-forms require fresh water for the transportation of substances and also to get rid of high amounts of wastes.

Question 3.
How are living organisms dependent on the soil? Are organisms that live in water totally independent of soil as a resource?
Answer:
All living organisms are directly or indirectly dependent on soil. Plants obtain water and minerals from the soil and prepare food for themselves and animals. Other organisms that live in water are not totally independent on soil because the microbes growing on the soil in water are the primary producers in the soil which start the food chain and even other microbes that live in soil help in the decomposition of dead plants and animals in water to return the nutrients and elements back to the water.

Question 4.
You have seen weather reports on television and in newspapers. How do you think we are able to predict the weather?
Answer:
Prediction of weather can be done by studying wind patterns which decide rainfall patterns. It also shows areas of low pressure and high pressure. In large parts of India, rains are mostly. brought by the South – West or North – East monsoons.

JAC Class 9th Science Solutions Chapter 14 Natural Resources

Question 5.
We know that many human activities lead to increasing levels of pollution of the air, water-bodies and soil. Do you think that isolating these activities to specific and limited areas would help in reducing pollution?
Answer:
If the human activities which lead to increasing levels of air, water and soil pollution are spread in wider area, the pollutants will spread more, but if these are limited and confined to a place, the soil and water pollution can be controlled to some extent and air pollution can also be minimised.

Question 6.
Write a note on how forests influence the quality of air, soil and water resources.
Answer:
Forests influence the quality of air, soil and water resources in various ways. Some of them are as follows:
1. Forests balance the percentage of carbon dioxide and oxygen in the atmosphere. The increasing amount of carbon dioxide caused by human activities is balanced by a larger
intake of carbon dioxide by plants during the process of photosynthesis. Simultaneously, a large amount of oxygen is released.

2. Forests prevent soil erosion. Roots of plants bind the soil tightly in a way that the surface of the soil cannot be eroded away by wind, water, etc.

3. Forests help in the replenishment of water resources. During the process of transpiration, a huge amount of water vapour goes into the air and condenses to form clouds. These clouds cause rainfall that recharges water bodies. Also, roots of plants facilitate the seepage of rainwater into the ground and help to recharge the water table.

JAC Class 9 Science Solutions

JAC Class 9 Maths Notes Chapter 11 रचनाएँ

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Students should go through these JAC Class 9 Maths Notes Chapter 11 रचनाएँ will seemingly help to get a clear insight into all the important concepts.

JAC Board Class 9 Maths Notes Chapter 11 रचनाएँ

रचनाएँ (Constructions ) : प्रमेय सिद्ध करते समय या उन पर आधारित प्रश्नों को हल करते समय जो आकृतियाँ बनाते हैं, वे साधारण चित्र होते हैं। इन चित्रों में इतनी परिशुद्धता नहीं होती। लेकिन ज्यामितीय रचनाओं में ज्यामितीय यन्त्रों जैसे अंशांकित रूलर, चाँदा (protractor), सेट स्क्वायर, परकार, इत्यादि का प्रयोग आवश्यक होता है। ज्यामितीय रचना में तर्क और कौशल का समावेश होता है। रचना यथार्थ और शुद्ध (accurate) होती है।

रचना करते समय ध्यान रखना चाहिए कि

  • आकृति शुद्ध और स्वच्छ हो, रबर (eraser) का कम-से-कम प्रयोग करना चाहिए। किसी भी रचना से पूर्व सम्बन्धित आकृति का कच्चा चित्र बना लेने से रचना करना सुगम हो जाता है।
  • रचना से सम्बन्धित समस्त बिन्दु तथा रेखाएँ स्पष्ट तथा यथा सम्भव चौड़ाई रहित होने चाहिए।
  • रचना हेतु खींची गयी सहायक रेखाओं को बिन्दु रेखाओं (dotted lines) द्वारा तथा मुख्य रेखाओं को अधिक स्पष्ट खींचना चाहिए।
  • रचना के समस्त पद क्रमशः लिखे जाने चाहिए।

JAC Class 9 Maths Notes Chapter 11 रचनाएँ

त्रिभुजों की रचनाएँ (Constructions of Triangles) : प्रत्येक त्रिभुज में छ: अवयव होते हैं, तीन भुजाएँ और तीन कोण। इन प्रतिबन्धों के अनुसार त्रिभुज की रचना करने के लिए कम से कम तीन स्वतन्त्र अवयव आवश्यक होते हैं :

  • तीन भुजाएँ, या
  • दो भुजाएँ और उनके बीच का कोण, या
  • दो कोण और एक भुजा, या
  • समकोण त्रिभुज में कर्ण और एक भुजा।

JAC Class 9 Science Notes Chapter 1 Matter in Our Surroundings

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JAC Board Class 9th Science Chapter 1 Notes Matter in Our Surroundings

→Matter: Everything in this universe is made up of material which is called matter. Matter is anything that has mass and occupies space. Matter is made up of lots of tiny particles.

→ Characteristics of particles of matter:
a. Particles of matter have space between them.
b. Particles of matter are continuously moving.
c. Particles of matter attract each other. Matter exists in three different states, viz., solid, liquic and gas.

Solid Liquids Gas
1. Strong intermolecular force of attraction. 1. Weak intermolecular force of attraction. 1. Very weak intermolecular force of attraction.
2. Very less intermolecular space. 2. Large intermolecular space. 2. Very large intermolecular space.
3. Have definite shape and volume. 3. No definite shape but definite volume. 3. No definite shape and volume.
4. High density, high melting and boiling points. 4. Density is lower, low melting and boiling points. 4. Density is very low.
5. Solids cannot be compressed. 5. Liquids can be compressed. 5. Gases are highly compressible.
6. Solids cannot flow. 6. Liquids can flow. 6. Gases can flow.

→ Matter can change its state from solid to liquid and from liquid to gas and vice-versa.
JAC Class 9 Science Notes Chapter 1 Matter in Our Surroundings 2

→ Effect of Temperature: On increasing temperature, the particles gain energy and start vibrating with greater energy. Due to increased kinetic energy, the particles overcome the force of attraction and a new state is obtained.

→ Melting Point: It is the temperature at which a solid becomes a liquid at atmospheric pressure. Boiling Point: It is the temperature at which a liquid changes into its vapour form at atmospheric pressure.

JAC Class 9 Science Notes Chapter 1 Matter in Our Surroundings

→ Latent Heat of Fusion: The amount of heat energy required to change 1 kg of a solid into liquid at its melting point is called the latent heat of fusion of the solid.

→ Latent Heat of Vaporisation: The amount of heat energy required to change 1 kg of a liquid into vapour at atmospheric pressure, at its boiling point is called the latent heat of vaporisation of the liquid.

→ Sublimation: It is the change of state directly from solid to gas or vice-versa without going through the liquid state. Evaporation: It is a surface phenomenon in which a liquid changes into vapour/gas below its boiling point. It results in lowering of temperature, i.e., cooling is caused when evaporation takes place.

→ Factors affecting Evaporation: An increase in surface area increases the rate of evaporation. An increase in temperature increases the rate of evaporation. A decrease in humidity increases the rate of evaporation. An increase in wind speed increases the rate of evaporation.

→ Some measurable quantities and their units:

Quantity SI Unit A Symbol
Temperature kelvin K
Length metre m
Mass kilogram kg
Weight newton N
Volume cubic metre m3
Density kilogram per cubic metre kg/m3
Pressure v pascal Pa

JAC Class 9 Science Notes

JAC Class 9 Science Notes Chapter 13 Why Do We Fall Ill

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JAC Board Class 9th Science Chapter 13 Notes Why Do We Fall Ill

→ Health: Health is a state of being free from illness or injury. According to the World Health Organisation (WHO), health is defined as a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity.

→ Conditions essential for Good Health:

  • Balanced and nutritious diet.
  • Personal hygiene.
  • Clean environment and surroundings.
  • Healthy and pollution free air in the surroundings.
  • Regular exercise.
  • Proper rest.
  • Good standard of living and economic status.

→ Disease: When the body is not at ease, i.e., comfortable, it is said to have a disease. In this condition, the functioning or appearance of one or more systems of the body changes. Depending on the duration, diseases are classified as acute or chronic.
a. Acute diseases: The diseases which last for a short duration of time are called acute diseases. Being of short duration, the acute diseases are unable to cause major ill effects on health, for example, common cold, malaria, typhoid, etc.

b. Chronic diseases: The diseases which last for a long duration of time or even for a lifetime are called chronic diseases. As these diseases remain in the body for a long time, their effects on the body are severe, e.g., diabetes, tuberculosis, etc.

JAC Class 9 Science Notes Chapter 13 Why Do We Fall Ill

→ Causes of a disease:
a. Immediate cause: The organisms that enter our body and cause diseases are called immediate causes, for example, virus, bacteria, protozoa, etc.

b. Contributory cause: The secondary factors which cause these organisms to enter our body are called contributory causes, e.g., dirty water, unclear surroundings, contaminated food, improper nourishment, poverty, poor standard of living, etc.

→ Diseases may be infectious or non- infectious
a. Infectious diseases: Diseases, where microbes are the immediate cause, are called infectious diseases. The infectious diseases spread from one person to another.
b. Non-infectious diseases: Some diseases that do not spread in the community but remain internal are called non-infectious diseases. Example: cancer, genetic abnormalities, high blood pressure, etc.

→ Infectious diseases: When a disease causing organism enters our body, it causes infection. It multiplies and grows in the body of the host.

Pathogen Diseases
Bacteria Tuberculosis, tetanus, typhoid, cholera
Virus AIDS, polio, chickenpox, rabies, measles
Fungi Skin diseases, food poisoning
Protozoan Malaria, amoebiasis, kala-azar
Worm Filariasis

→ Infectious diseases spread through:

  • Air: This occurs through the little droplets thrown out by the infected person who sneezes or coughs. Someone standing closeby can breathe in these droplets and the microbes get a chance to start a new infection. Examples: common cold, pneumonia, tuberculosis.
  • Water: This occurs if excreta of someone suffering from an infectious disease, such as cholera, gets mixed with the drinking water used by the people nearby. The cholera causing microbes will enter new hosts through the water they drink and cause disease in them.
  • Contact: Many diseases spread by contact of the infected person with the healthy person. Examples: fungal infection, scabies, etc. AIDS and syphilis spread by sexual contact.
  • Body fluids: Infected body fluids like blood, semen, mother’s milk etc., when in contact, can also cause diseases. Example-AIDS.

JAC Class 9 Science Notes Chapter 13 Why Do We Fall Ill

→ Antibiotics: Antibiotics are the drugs that kill bacteria. They commonly block the biochemical pathways important for bacteria. Many bacteria make a cell wall to protect themselves. The antibiotic penicillin blocks the bacterial processes that build the cell wall. As a result, the growing bacteria become unable to make cell walls and die easily.

→ Inflammation: When an active immune system releases many cells at the affected tissue to kill-off the disease-causing microbes, it is called inflammation. Local effects caused in the body due to inflammation are – swelling, pain, fever and redness.

→ Principles of Treatment: There are two methods for the treatment of diseases:
a. by reducing the symptoms of the diseases.
b. by killing the microbes.

→ Principles of Prevention: These are the ways to prevent the diseases.
a. General ways: The general ways of preventing infections mostly relate to preventing exposure to the diseases. We can prevent exposure to the infectious microbes as follows:

  • For air-borne infections: We can prevent exposure by providing living conditions that are not over crowded.
  • For water-borne infections: We can prevent exposure by using safe drinking water. This can be done by treating the water for any microbial contamination.
  • For vector-borne infections:

We can prevent exposure by providing clean environment which are free from mosquitoes, flies, rats, etc.
Another general way of preventing the diseases is the availability of proper and sufficient food for everyone. This will help the immune system to become healthy and work properly for fighting off the microbes causing the disease.

b. Specific ways: By giving vaccines, i.e., childhood immunisation that is given to the children for preventing infectious diseases. During vaccination, we put dead or weakened pathogens in the body that mimics antigens we want to vaccinate against. This does not actually cause the disease but this would prevent any further exposure to the infecting microbes from turning into actual disease. Vaccinations are available for the following diseases: tetanus, diphtheria, whooping cough, measles, polio, rabies, etc.

JAC Class 9 Science Notes

JAC Class 9 Science Notes Chapter 12 Sound

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JAC Board Class 9th Science Chapter 12 Notes Sound

→ Sound: Sound is a form of energy which produces a sensation of hearing in our ears.

→ Production of Sound: Sound is produced due to the vibration of objects. Vibration is a periodic back-and-forth motion of the particles of an elastic body or medium about a central position. It is also called as oscillation.
For example:
a. Strings of a guitar vibrate to produce sound when stretched.
b. When membrane of a table is struck, it vibrates to produce sound.

JAC Class 9 Science Notes Chapter 12 Sound

→ Propagation of Sound
a. The travelling of sound is called propagation of sound. Sound is propagated by the to and fro motion of particles of the medium.

b. When an object vibrates, the particles in the medium vibrate. The particle in contact with the vibrating object is first displaced from its equilibrium position. Each particle disturbs the other particle in contact. Thus, the disturbance is carried from the source to the listener.
JAC Class 9 Science Notes Chapter 12 Sound 1
c. Only the disturbance produced by the vibrating body travels through the medium, but the particles do not move forward themselves. Sound waves cannot travel in vacuum.

→ Medium: The matter or substance through which sound is transmitted is called a medium. It can be solid, liquid or gas. Air is the most common medium for sound propagation.

→ Wave: Wave is a disturbance in which energy is transferred from one point to another without any direct contact between them.
For example: heat, light and sound are considered as waves.

→ Types of Waves
On the basis of direction of propagation, waves are categorised into two types:
a. Longitudinal waves: These are the waves in which the particles of the medium vibrate along the direction of propagation of the wave. For example: sound wave.
b. Transverse waves: In this type of wave, the particles of the medium vibrate in a direction perpendicular to the direction of propagation of the wave. For example: waves produced in a stretched string.

Another type of waves which do not require any medium for propagation are called electromagnetic waves. These waves can travel through vacuum. For example, light waves and X-rays.

→ Compressions and Rarefactions

  1. Compression is the part of wave in which particles of the medium are close to one another forming a region of high pressure and density. Compressions are represented by the upper portion of the curve called crest.
  2. Rarefaction is the part of wave where particles spread out to form a region of low pressure and density. Rarefactions are represented by the lower portion of the curve called trough.

JAC Class 9 Science Notes Chapter 12 Sound 2

→ Wavelength: Distance between two consecutive crests or troughs is called wavelength. Wavelength is represented by λ (lambda) and its SI unit is metre.

→ Frequency: Number of oscillations of a sound wave per unit time is called its frequency. The number of crests or troughs per unit of time will give the frequency. Its SI unit is hertz (Hz).

→ Time period: The time taken to complete one vibration is called time period. It is denoted by ‘T’. Its SI unit is second (s). The frequency of a wave is the reciprocal of the time period.
v = \(\frac{1}{\mathrm{~T}}\); where v is the frequency and T is the time period.

→ Amplitude: The magnitude ofthe maximum disturbance in the medium, on either side of the mean value, is called the amplitude of the wave. It is usually represented by the letter ‘A’. Its unit is metre.

JAC Class 9 Science Notes Chapter 12 Sound

→ Velocity: The distance travelled by a wave in one second is called velocity of the wave or speed of the wave. Its SI unit is metre per second (m s-1).
Velocity = \(\frac{\text { Distance travelled }}{\text { Time taken }}\)
v = \(\frac{\lambda}{\mathrm{T}}\), where λ = wavelength of the wave travelled and T is the time period.
v = λv (As \(\frac{1}{\mathrm{~T}}\) = v, where v is called frequency of the wave)
Thus, Velocity = Wavelength × Frequency
v = λv is called the wave equation.

→ Pitch and Loudness of Sound
a. Pitch: It represents shrillness or flatness of sound. It depends on the frequency of vibration. The higher the frequency of sound wave, the higher will be the pitch of sound and vice-versa.
b. Loudness: It is the measure of the sound energy reaching the ear per second. It depends on the amplitude of the sound wave. It is measured in decibel ‘dB’.

→ Music and Noise
a. Music: It is the sound that is pleasant to hear. For example, sound coming from the musical instruments.
b. Noise: It is the sound that is unpleasant to hear. For example, sound produced by vehicles.

→ Tone and Note
a. Tone: A pure sound of single frequency is called tone.
b. Note: An impure sound produced by a mixture of many frequencies is called a note. For example, a musical note has tones of various frequencies.

→ Audible Frequency: The audible range of human ear is 20 Hz to 20,000 Hz, i.e., human ear can hear only those waves whose frequencies fall between 20 Hz and 20,000 Hz.

→ Infrasonic sound: Sound whose frequency is less than 20 Hz is called infrasonic sound. Ultrasonic sound: Sound whose frequency is more than 20,000 Hz is called ultrasonic sound.

→ Uses of ultrasonic sound: Ultrasonic sound is used to clean objects like electronic components, to detect cracks in metal blocks, in ultrasound scanners for getting images of internal organs of the human body, to break small stones formed in the kidneys into fine grains, etc.

→ Reflection of Sound: Sound reflects off a surface in the same way as light reflects and follows the same rules of reflection. Hard surfaces reflect sound better than the soft ones.

JAC Class 9 Science Notes Chapter 12 Sound

→ Laws of reflection of sound

  • The directions in which the sound is incident and reflected make equal angles with the normal to the reflecting surface at the point of incidence.
  • The incident sound wave, the reflected sound wave and the normal all, lie in the same plane.
  • The reflection of sound has many applications such as stethoscopes, horns, megaphones, designing of concert halls, etc.

→ Echo: In bigger monuments and in large empty halls, you can hear reflections of your sound after you speak something. This effect is known as echo. For hearing a distinct echo, the time interval between the original sound and the reflected one must be at least 0.1 s.

Since the speed of sound in air is 344 m/s, the distance travelled by sound in 0.1 s is 34.4 m. So, to hear an echo clearly and distinctly, the minimum distance of the reflecting surface from the source of sound should be half of this distance, i.e., 17.2 m.

→ Reverberation: The persistence of sound in an auditorium as a result of repeated reflections of sound is called reverberation.

→ Sonar: It is a device which uses ultrasonic waves to measure the distance, direction and speed of underwater objects. The distance of the object can be calculated by knowing the speed of sound in water and the time taken between the transmission and reception of ultrasound.
JAC Class 9 Science Notes Chapter 12 Sound 3

→ Structure of the human ear: The sound waves pass through the ear canal onto a thin membrane called eardrum. The eardrum vibrates and the vibrations are amplified by the three bones of the middle ear called malleus, incus and stapes. Middle ear then transmits the sound waves to the inner ear. The brain then interprets the signals as sound.
JAC Class 9 Science Notes Chapter 12 Sound 4

→ Supersonic speed: When a body moves in air with a speed greater than the speed of sound, it is said to have a supersonic speed.

→ Shock wave: When a supersonic aircraft moves through air, it leaves behind itself a conical region of disturbance which spreads continuously. Such a disturbance is called a shock wave. Shock waves travel at supersonic speeds and carry a huge amount of energy.

JAC Class 9 Science Notes

JAC Class 9 Science Notes Chapter 11 Work and Energy

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JAC Board Class 9th Science Chapter 11 Notes Work and Energy

→ Work: When a force acts upon an object to cause a change in its position, work is said to be done. It is expressed as the product of force and displacement in the direction of force.
W = F × s
Here, W = work done on the object
F = force on the object
s = displacement of the object
The SI unit of work is newton metre (N m) or joule (J).
1 joule is defined as the amount of work done by a force of 1 N to cause a displacement of 1 m in the object.

JAC Class 9 Science Notes Chapter 11 Work and Energy

→ Sign Conventions for Work Done
a. When both force and displacement are in the same direction, work done is positive.
W = (F × S)

b. When force acts in a direction opposite to the direction of displacement, the work done is negative.
W = – (F × S)
Angle between force and displacement is 180°.

c. If force and displacement are inclined at an angle less than 180°, the work done is given by:
W = Fs cos θ
where θ is the angle between force and displacement.

d. If force and displacement act at an angle of 90°, the work done is zero.

→ Necessary Conditions for Work to be done
Two conditions are required for the work to be done:
a. A force should act on the object.
b. Object must be displaced.

→ Energy: The capacity of a body to do work is called energy of the body. It is a scalar quantity.

→ Unit of energy: As energy is measured by the amount of work that a body can do, so the unit of energy is same as that of work. The SI unit of energy is joule (J). One joule of energy is the energy required to do 1 J of work.
1 kilojoule = 1 kJ = 1000 J.

→ Forms of energy: The various forms of energy are potential energy, kinetic energy, heat energy, chemical energy, electrical energy and light energy.

→ Kinetic energy: It is the energy possessed by a body by the virtue of its motion. Kinetic energy of an object increases with its speed. Kinetic energy of a body moving with a certain velocity is equal to the work done on it to make it acquire that velocity.

→ Derivation
Let an object of mass’m’, start from rest and attain a uniform velocity ‘v’, after a force ‘F’ is applied on it.
Let, during this period, the object be displaced by a distance ‘s’.
Thus, work done on the object,
W = F × S …(i)

Let the acceleration produced after applying force on the object be ‘a’.
So, using third equation of motion, we have:
v2 – u2 = 2as ……….(ii)

Substituting F and s from equations (ii) and (iii) in equation (i), we get:
W = F × s
W = ma × \(\frac{v^{2}-u^{2}}{2 a}\)
W = \(\frac{1}{2}\)mv2 [As, initial velocity, u = 0]
∴ KE = \(\frac{1}{2}\)mv2
[Work done is stored as kinetic energy]

JAC Class 9 Science Notes Chapter 11 Work and Energy

→ Potential energy: The energy possessed by a body due to its position, shape or configuration is called its potential energy.

→ Gravitational potential energy (PE): The gravitational potential energy (PE) of an object at a point above the ground is defined as the work done in raising it from the ground to that point, against gravity.
JAC Class 9 Science Notes Chapter 11 Work and Energy 1

→ Derivation:
Consider a body of mass m, raised through a height ‘h’ from the ground.
Force required to raise the object = weight of the object = mg.
Object gains energy equal to the work done on it.
Work done on the object against gravity is ‘W’.
W = force × displacement = mg × h
W = mgh
PE = mgh
[Work done is stored as potential energy]

→ Mechanical energy:
The sum of kinetic energy and potential energy is called mechanical energy.

→ Law of Conservation of Energy:
It states that energy can neither be created nor destroyed, but it can be transformed from one form to another. The total energy before and after the transformation always remains constant in an isolated system.
JAC Class 9 Science Notes Chapter 11 Work and Energy 2
Potential energy + Kinetic energy = Constant (Mechanical energy)
Consider a body of mass ‘m’, raised to a height ‘h’ as shown in the figure. At A, its potential energy is maximum and kinetic energy is 0 as it is stationary.

When body falls at B, ‘h’ is decreasing, hence potential energy decreases. Also, v is increasing, therefore, kinetic energy is increasing.
When the body is about to reach the ground level, h = 0 and ‘v’ will be maximum. Hence, kinetic energy > potential energy.
This shows that decrease in potential energy = increase in kinetic energy.
Thus, there is a continuous transformation of gravitational potential energy into kinetic energy.

JAC Class 9 Science Notes Chapter 11 Work and Energy

→ Power: The rate of doing work is called power.
Power = \(\frac{\text { Work }}{\text { Time }}\) or P = \(\frac{\mathrm{W}}{\mathrm{t}}\)
Work, power and energy are all scalar quantities.

→ Watt: It is the SI unit of power. The power of an agent is one watt if it does work at the rate of 1 joule per second.
1 watt = \(\frac{1 \text { joule }}{1 \text { second }}\) or 1 W = 1 J s-1
1 kilowatt = 1000 watt or 1 kW = 1000 W
1 horsepower = 746 watt or 1 H.P. = 746 W

→ Kilowatt-hour (kWh): It is the commercial unit of electric energy. It is defined as the electric energy consumed by an appliance of power 1000 watt in one hour.
1 kWh = 3.6 × 106 J

JAC Class 9 Science Notes

JAC Class 9 Science Notes Chapter 10 Gravitation

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JAC Board Class 9th Science Chapter 10 Notes Gravitation

→ Gravitation:
The universal law of gravitation’ states that any two bodies having mass, attract each other with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. The force acts along the line joining the centres of the objects.
JAC Class 9 Science Notes Chapter 10 Gravitation 1
Here, G is universal gravitational constant with a value of 6.673 × 10-11 N m2 kg2. The value of G was found out by Henry Cavendish.

Note:

  • If mass of an object is large, force will be more. If mass of an object is small, force will be less.
  • If distance between two objects is more, force exerted will be less and vice versa.

JAC Class 9 Science Notes Chapter 10 Gravitation

→ Importance of Gravitational Force

  • It binds us to the earth.
  • Moon revolves around the earth due to gravitational force. Planets revolve around the sun due to gravitational force.
  • Tides in oceans are caused due to gravitational force of the moon on earth.

→ Centripetal acceleration of the moon:
If the moon is revolving with speed v in a circular orbit of radius r, then the acceleration acting on it along the radius and towards the centre of its orbit is
ac = \(\frac{\mathrm{v}^{2}}{\mathrm{r}}\)

→ Free fall: The earth attracts objects towards it due to gravitational force. When an object moves under the influence of gravitational force alone, it is said to be in a ‘free fall’.

→ Acceleration due to gravity: The acceleration produced in the bodies due to earth’s gravity is called acceleration due to gravity. Its value on the earth’s surface is 9.8 m/s2.

→ Relations between g and G: If M is the mass of the earth and R is its radius, the acceleration due to gravity at the surface of the earth is given by
g = \(\frac{\mathrm{GM}}{(\mathrm{R})^{2}}\)

The value of g depends on:

  • shape of the earth
  • height above the earth
  • depth inside the earth
  • latitude on the earth

→ Mass of the earth:
It is given by
M = \(\frac{g^{2}}{G}\)

→ Centre of mass:
The centre of mass of a body may be defined as the point at which whole mass of the body may be assumed to be concentrated.

→ Centre of gravity:
The centre of gravity of a body is a point at which the resultant of all the parallel forces due to gravity, experienced by various particles of the body, acts or at which whole weight of the body acts.

→ Equations of motion for freely falling bodies: The three equations of motion are:
v = u + at ……..(ii)
s = ut + \(\frac{1}{2}\) at2 …..(ii)
v2 – u2 = 2as
For free fall, the value of acceleration (a)
= g = 9.8 ms-2

→ Projectile: Any object thrown into space with some initial velocity and which thereafter moves under the influence of gravity alone is called a ‘projectile’. The path of a projectile is a parabola. Its horizontal range is maximum when the angle of projection is 45°.

JAC Class 9 Science Notes Chapter 10 Gravitation

→ Mass: Mass of an object is the measure of its inertia. It is the amount of matter present in it. It remains the same everywhere in the universe.

→ Weight: The force with which an object is attracted towards the centre of the earth is known as the weight of that object. Its SI unit is newton.
W = m × g
where W = weight of the object, m = mass of the object, and g = acceleration due to gravity.
The weight of an object can change from one place to the other and from one planet to the other.

→ Thrust: It is the net force applied in a particular direction. Its SI unit is N.
Pressure = \(\frac{\text { Thrust }}{\text { Area }}\)
The SI unit of density is kg/m3.

→ Relative density: It is the ratio of the density of a substance to the density of water at 4°C.
Density of substance Density of water at 4°C
Since relative density is a pure ratio, it has no units.

→ Pressure in fluids:
All liquids and gases are fluids as they can flow. The pressure exerted by a fluid is transmitted in all directions.

→ Buoyancy:
The upward force exerted by water (fluid) on the body immersed in it is known as upthrust or buoyancy. The magnitude of the buoyant force depends of the density of the fluid.

→ Archimedes’ principle: It states that when a body is immersed fully or partially in a fluid, it experiences an upward force that is equal to the weight of the fluid displaced by it.
It has following applications:

  • Used in designing ships and submarines.
  • In lactometers to find purity of milk.
  • In hydrometers to determine the density of a liquid.

JAC Class 9 Science Notes Chapter 10 Gravitation

→ Density: The density of a substance is its mass per unit volume.
Density = \(\frac{\text { Mass }}{\text { Volume }}\)
The SI unit of density is kg/m3.

→ Relative density: It is the ratio of the density of a substance to the density of water at 4°C.
Density of substance Density of water at 4°C
Since relative density is a pure ratio, it has no units.

JAC Class 9 Science Notes

JAC Class 9 Science Notes Chapter 9 Force and Laws of Motion

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JAC Board Class 9th Science Chapter 9 Notes Force and Laws of Motion

→ Force: It is a push or pull on an object that produces acceleration in the body on which it acts. The SI unit of force is ‘newton’. Forces are used in our daily life actions like pushing, lifting, pulling, stretching, twisting and pressing.

→ A force cannot be seen. It can be judged only by the effects which it can produce in several bodies (or objects) around us.

→ Force has both magnitude and direction, making it a vector quantity. It is measured in the SI unit of newton and represented by the symbol ‘F’

JAC Class 9 Science Notes Chapter 9 Force and Laws of Motion

→ Effects of Force:
a. Force can set a stationary body in motion. For example, a football can be set in motion by kicking it, i.e. by applying a force.

b. Force can stop a moving body. For example, by applying brakes, a running cycle or a running vehicle can be stopped.

c. Force can change the direction of a moving object. For example, by applying force, i.e., by moving handle, the direction of a running bicycle can be changed. Similarly by moving steering, the direction of a running vehicle is changed.

d. Force can change the speed of a moving body. For example, by accelerating, the speed of a running vehicle can be increased or by applying breaks, the speed of a running vehicle can be decreased.

e. Force can change the shape and size of an object. For example, by hammering, a block of metal can be turned into a thin sheet. Also by hammering, a stone can be broken down into pieces.

→ Balanced forces: If the resultant force of several forces acting on a body is zero, the forces are said to be ‘balanced forces’.

→ Unbalanced forces: If the resultant force of the several forces acting on a body is not zero, the forces are said to be ‘unbalanced forces’. An object in rest can be moved by applying unbalanced forces. Only an unbalanced force can produce the effects of force.

→ Newton’s First Law of Motion: An object remains in its state of rest or of uniform motion in a straight line unless acted upon by an external unbalanced force.

→ Inertia: The natural tendency of an object to resist a change in its state of rest or of uniform motion is called its inertia.

  • Inertia of rest: It is the tendency of a body to remain in its state of rest.
  • Inertia of motion: It is the tendency of a body to remain in its state of uniform motion in a straight line.
  • Inertia of direction: It is the inability of a body to change, by itself, its direction of motion.

JAC Class 9 Science Notes Chapter 9 Force and Laws of Motion

→ Newton’s Second Law of Motion: The rate of change of momentum of an object is proportional to the applied unbalanced force in the direction of force.
Mathematically,
Force = Mass × Acceleration or,
F ∝ \(\frac{P_{1}-P_{2}}{t}\) or \(\frac{\mathrm{m}(\mathrm{v}-\mathrm{u})}{\mathrm{t}}\) or ma
This law defines the unit of force. One unit force is that force which produces unit acceleration in a body of unit mass.

→ Newton (N): It is the SI unit of force. One Newton is that force which produces an acceleration of lm/s2 in a body of mass 1 kg.

→ 1 newton = 1 kg × 1 m/s2 or 1N = 1 kg m/s2

→ Momentum: The momentum of an object is the product of its mass and velocity and has the same direction as that of the velocity. Its SI unit is kg m/s.
Momentum = Mass × Velocity or p = mv

→ Newton’s Third Law of Motion: To every action, there is an equal and opposite reaction and they act on two different bodies.

→ Law of Conservation of Momentum:
It states that the total momentum of any system of objects remains constant in the absence of any external force. According to the law of conservation of momentum, for collision between two bodies:
Total momentum before collision = Total momentum after collision
m1u1 + m2u2 = m1v1 + m2v2

→ Frictional force: Whenever a body slides or rolls over the surface of another body, a force comes into action which acts in the opposite direction as that of the motion of a body. This opposing force is called ‘friction’.

JAC Class 9 Science Notes