Students must go through these JAC Class 10 Science Notes Chapter 13 Magnetic Effects of Electric Current to get a clear insight into all the important concepts.
JAC Board Class 10 Science Notes Chapter 13 Magnetic Effects of Electric Current
→ Magnet: A magnet is a piece of magnetic material, occuring naturally or made artificially by magnetizing iron or steel, which attracts pieces of magnetic substances such as iron, nickel and cobalt.
→ Magnetic field: The region surrounding a magnet in which the force of attraction and repulsion due to that magnet can be detected (using magnet or magnetic substances) is called the magnetic field.
[Each point in this field has a particular strength. The field at each point also has a definite direction.]
→ Magnetic field lines : The lines along which the iron filings align / arrange themselves due to force acting on them in the magnetic field of a bar magnet are called magnetic field lines.
Note : The path followed by the north pole of a compass needle (magnetic needle) placed in a region of magnetic field, such as that of a bar magnet, is called a magnetic field line. It shows how the magnetic force changes from point to point.
→ Characteristics of magnetic field lines:
- The magnetic field lines emerge from north pole and merge at the south pole outside the magnet, while inside the magnet the direction of field lines is from its south pole to its north pole.
Thus, the magnetic field lines are closed and continuous curve.
- The magnetic field lines are crowded near the pole where the magnetic field is strong and are far apart near the middle of the magnet and far from the magnet where the magnetic field is weak.
- The magnetic field lines never intersect each other because if they do so, there would be two directions of magnetic field at that point which is absurd.
- In case the field lines are parallel and equidistant, these represent a uniform magnetic field.
Important note: The relative strength of the magnetic field is shown by the degree of closeness of the field lines.
→ Oersted’s observations : When a magnetic needle is placed near a conducting wire carrying a current, the magnetic needle deflects. The deflection is observed in the opposite direction, when the direction of the current is reversed. This shows that when an electric current passes through a conducting wire a magnetic field is produced around it.
→ Magnetic field due to a current through a straight conductor: The magnetic field lines due to a current through a straight conductor form concentric circles around the conductor. The strength of this magnetic field is proportional to the current through the conductor and inversely proportional to the distance of the given point from the conductor.
→ Right-hand thumb rule: Imagine that you are holding a current-carrying straight conductor in your right hand such that the thumb points towards the direction of current. Then your fingers of right hand wrap around the conductor in the direction of the field lines of the magnetic field.
→ Magnetic field due to a current through a circular loop: The magnetic field lines due to a current through a circular loop form concentric circles. These circles become larger and larger as we move away from the wire and at the centre of the circular loop, the arcs of these large circles appear as straight lines. The magnetic field at the centre of the circular loop is proportional to the current through the loop and inversely proportional to the radius of the circular loop.
→ Solenoid: A coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder is called a solenoid. The magnetic field due to a current in a solenoid is similar to that of a bar magnet. The magnetic field lines inside a solenoid are straight lines parallel to each other. The magnetic field inside a solenoid is uniform.
→ Electromagnet: An electromagnet is a magnet consisting of a long coil of insulated copper wire wound around a soft iron core in the form of a rod. It is magnetised only when an electric current is passed through the coil.
→ Force on a current- carrying conductor placed in a magnetic field: When a conductor carrying an electric current is placed in a magnetic field, magnetic force acts on it. This force is perpendicular to the direction of the magnetic field as well as the direction of the current and is proportional to the electric current, magnetic field of the magnet, the length of the conductor inside the magnetic field and on the angle between the directions of the magnetic field and the current. It is maximum when this angle is 90°. The direction of this force can be determined using Fleming’s left-hand rule.
→ Fleming’s left-hand rule: Stretch the thumb, forefinger and middle finger of your left hand such that they are mutually perpendicular. If the first (fore) finger points in the direction of magnetic field and second (middle) finger points in the direction of current, then the thumb will point in the direction of motion or the force acting on the conductor.
→ Electric motor: It converts electrical energy into mechanical energy. In this case, a current-carrying coil kept in a strong magnetic field experiences a force. As a result, the coil starts rotating.
→ Electromagnetic induction: The process, by which a changing magnetic field in a conductor induces a current in another conductor is called electromagnetic induction.
An electric current produced in a closed circuit by a changing magnetic field is called an induced current. This phenomenon is called electromagnetic induction.
→ Induced potential difference (or electromotive force): Because of the rate of change of number of magnetic field lines linked with the loop during the relative motion of a magnet and loop or due to a changing current in a nearby conductor, an electric potential difference is induced in the coil. It is called induced potential difference (or electromotive force).
The electromotive force induced in a loop is proportional to the rate of change of number of magnetic field lines associated with the loop and the number of turns of a loop.
→ Fleming’s right-hand rule : Stretch the thumb, forefinger and middle finger of right hand so that they are perpendicular to each other. If forefinger indicates the direction of the magnetic field and thumb shows the direction of motion of conductor, then the middle finger will show the direction of induced current.
→ Electric generator: It converts mechanical energy into electrical energy. Its working is based on electromagnetic induction. The generator by which a unidirectional current (DC) can be obtained is called a DC generator and that by which an alternating current (AC) is obtained is called an AC generator.
→ Direct Current (DC) and Alternating Current (AC) : If a current flows only in one direction, it is called a direct current (DC). DC is obtained with a battery and DC generator.
The current whose direction changes periodically with time is called an alternating current (AC). AC is obtained with an AC generator.
→ Domestic electric circuits: In India, the AC voltage used for domestic purposes is 220 V and its frequency is 50 Hz. Three wires, namely live, neutral and earthing wire enter our house through a main fuse passing through an electric meter at the meter-board. The potential difference between the live and neutral wire is 220 V.
The earthing wire is connected to a copper plate placed in a deep pit dug near the house. This wire is connected to the metallic body of the appliances, so that one does not experience shock.
Two types of electric lines are available for domestic usage. One is of 5 A and other is of 15 A rating. The entire wiring of the house is done in parallel connections.
→ Fuse : An electric fuse is an important component of all domestic circuits. It is used to avoid incidents such as electric shock, fire, damage to an electric appliance due to (a) short-circuiting or (b) overloading (drawing a current beyond a specified limit) in a circuit. A fuse is a most important safety device. It consists of a short, thin, tin-plated copper wire having low melting point. It melts and breaks the circuit if the current exceeds a safe value.
A fuse is always connected in series with the live wire and in the beginning of the circuit.