10 Question-Answer on heating effect of current
1. An electric lamp is marked 60 W, 240 V. if it operates at 200V, the current through it will be
(a) 0.18 A
(b) 0.21 A
(c) 0.25 A
(d) 0.30 A.
Ans: (b)
2. What will be the wattage of a 50W, 200 V lamp when used on 160V power supply?
(a) 32 W
(b) 64 W
(c) 96 W
(d) 128 W
Ans: ( a)
3. Overloading of an electric circuit implies
(a) Drawing of large current
(b) Connecting a number of electric devices in series with the power supply
(c) Connecting high resistance device
(d) None of the above
Ans: (a)
4. What is immaterial for an electric fuse?
(a) Its specific resistance
(b) Its length
(c) Its radius
(d) Current flowing through it.
Ans: (b)
5. Resistance of conductor is doubled keeping the potential difference across it constant. The rate of generation of heat will
(a) Become one forth
(b) Be halved
(c) Be doubled
(d) Become four times.
Ans: (b)
6. The potential difference across a conductor is doubled, the rate of generation of heat will
(a) Become one fourth
(b) Be halved
(c) Be doubled
(d) Becomes four times
Ans: (d)
7. Two electric bulbs whose resistances are in the ratio 1 : 3 are connected in parallel to a constant voltage source. The powers dissipated in them have the ratio:
(a) 1 : 3
(b) 1 : 1
(c) 3 : 1
(d) 1 : 9
Ans: ( c)
8. An electric kettle is rated at 500 W. the time taken to heat 0.5 litre of water from 30˚ C to 100˚ C in in this kettle is
(a) 7.9 minutes
(b) 3.9 minutes
(c) 4.9 minutes
(d) 5.9 minutes
Ans: (c)
9. How many calories of heat will be approximately developed in a 210 W electric bulb in 5 minutes
(a) 15000 cal
(b) 35000 cal
(c) 45000 cal
(d) 25000 cal
Ans: (a)
10. When a current is divided into two resistors according to Kirchhoff’s laws, then the heat produced is
(a) Zero
(b) Maximum
(c) Minimum
(d) Uncertain.
Ans: (c)