Case Study Question for Class 12 Physics Chapter 3 Current Electricity

Whenever an electric current is passed through a conductor, it becomes hot after some time. The phenomenon of the production of heat in a resistor by the flow of an electric current through it is called heating effect of current or Joule heating. Thus, the electrical energy supplied by the source of emf is converted into heat. In purely resistive circuit, the energy expended by the source entirely appears as heat. But if the circuit has an active element like a motor, then a part of energy supplied by the source goes to do useful work and the rest appears as heat. Joule’s law of heating forms the basis of various electrical appliances such as electric bulb, electric furnace, electric press etc.

(i) Which of the following is correct statement?
(a) Heat produced in a conductor is independent of the current flowing.
(b) Heat produced in a conductor varies inversely as the current flowing.
(c) Heat produced in a conductor varies directly as the square of the current flowing.
(d) Heat produced in a conductor varies inversely as the square of the current flowing.               

(ii) If the coil of a heater is cut to half, what would happen to heat produced?
(a) Doubled
(b) Halved
(c) Remains same
(d) Becomes four times.

(iii) A 25 W and 100 W are joined in series and connected to the mains. Which bulb will glow brighter?
(a) 100 W
(b) 25 W
(c) Both bulbs will glow brighter
(d) None will glow brighter

(iv) A rigid container with thermally insulated wall contains a coil of resistance 100 Ω, carrying 1 A. Change in its internal energy after 5 min will be
(a) 0 kJ
(b) 10 kJ
(c)20 kJ
(d) 30 kJ

(v) The heat emitted by a bulb of 100 W in 1 min is
(a) 100 J
(b) 1000 J            
(c) 600 J           
(d) 6000 J

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