Class Ten Science NCERT Solution Chapter 13
Chapter 13: Magnetic Effects of Electric Current
Q.11. State Fleming’s left-hand rule.
Ans. Fleming’s left-hand rule states that if we arrange the thumb, the centre finger, and the forefinger of the left hand at right angles to each other, then the thumb points towards the direction of the magnetic force, the centre finger gives the direction of current, and the forefinger points in the direction of magnetic field.
Q.12. What is the principle of an electric motor?
Ans. The working principle of an electric motor is based on the magnetic effect of current. A current-carrying loop experiences a force and rotates when placed in a magnetic field. The direction of rotation of the loop is given by Fleming’s left-hand rule.
Q.13. What is the role of the split ring in an electric motor?
Ans. The split ring in the electric motor acts as a commutator. The commutator reverses the direction of current flowing through the coil after each half rotation of the coil. Due to this reversal of the current, the coil continues to rotate in the same direction.
Q.14. Explain different ways to induce a current in a coil.
Ans. The different ways to induce a current in a coil are as follows:
(a) If a coil is moved rapidly between the two poles of a horseshoe magnet, then an electric current is induced in the coil.
(b) If a magnet is moved relative to a coil, then an electric current is induced in the coil.
Q.15. State the principle of an electric generator.
Ans. An electric generator works on the principle of electromagnetic induction. It generates electricity by rotating a coil in a magnetic field.
Q.16. Name some sources of direct current.
Ans. Some sources of direct current are an electric cell, Solar cell, DC generator, etc.
Q.17. Which sources produce alternating current?
Ans. AC generators, power plants, etc., produce alternating current.
Q.18. Choose the correct option.
A rectangular coil of copper wires is rotated in a magnetic field. The direction of the induced current changes once in each
(a) two revolutions
(b) one revolution
(c) half revolution
(d) one-fourth revolution
Ans. (c) When a rectangular coil of copper is rotated in a magnetic field, the direction of the induced current in the coil changes once in each half-revolution.
Q.19. Name two safety measures commonly used in electric circuits and appliances.
Ans. Two safety measures commonly used in electric circuits and appliances are as follows :
(i) Each circuit must be connected with an electric fuse. This prevents the flow of excessive current through the circuit. When the current passing through the wire exceeds the maximum limit of the fuse element, the fuse melts to stop the flow of current through that circuit, hence protecting the appliances connected to the circuit.
(ii) Earthing is a must to prevent electric shocks. Any leakage of current in an electric appliance is transferred to the ground and people using the appliance do not get the shock.
Q.20. An electric oven of 2 kW is operated in a domestic electric circuit (220 V) that has a current rating of 5 A. What result do you expect? Explain.
Ans. Current drawn by the electric oven can be obtained by the expression
P = VI
I = P/V
Current = I
Power of the oven, P = 2kW = 2000 W
Voltage supplied, V = 220 V
I = 2000/220 = 9.09 A
Hence, the current drawn by the electric oven is 9.09 A, which exceeds the safe limit of the circuit. Fuse element of the electric fuse will melt and break the circuit.