Electric Current Test

Result

Electric Current Test - 12

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Weekly Quiz Competition

Question 1
1 / -0

In the following question, Statement - 1 (Assertion) is followed by Statement - 2 (Reason). The question has the following four choices out of which only one choice is correct.
Statement - 1: A 60 W bulb is connected in parallel with a room heater and this combination is connected across the mains. If the 60 W bulb is replaced by a 100 W bulb, the heat produced by the heater will remain the same.
Statement - 2: When resistances are connected in parallel across the mains, the heat produced is inversely proportional to the resistance.

A
Statement - 1 is True, Statement - 2 is True; Statement - 2 is a correct explanation for Statement - 1.

B
Statement - 1 is True, Statement - 2 is True; Statement - 2 is NOT a correct explanation for Statement - 1.

C
Statement - 1 is True, Statement - 2 is False.

D
Statement - 1 is False, Statement - 2 is True.

Solution

The correct choice is (1). When a bulb and a heater are connected in parallel and this combination is connected across the mains, potential difference across each is the same equal to the voltage V of the mains, irrespective of the resistance of the bulb. If R is the resistance of the heater, the rate at which heat is produced will be V²/R in both cases.
Question 2
1 / -0

Two equal resistors, each of resistance R, connected in series across a voltage source V dissipate power P. What would be the power dissipated in the same resistors when they are connected in parallel across the same voltage source?

A
4P

B
2P

C
16P

D
P

Solution

Let R be the resistance of the identical two resistors. When they are connected in series across a voltage source V, the equivalent resistance of the combination is 2R and then total power dissipated by the resistors will be P = V²/2R.
When they are connected in parallel across the same voltage source V, the equivalent resistance of the combination is R/2, and then total power dissipated by the resistors will be V²/(R/2) = 4V²/2R = 4P.
Question 3
1 / -0

Two electrical devices of power ratings 1 kW and 2 kW are connected (a) in series and (b) in parallel. The ratio of the power ratings of the combination in case (a) to that in case (b) is

A
1 : 4

B
1 : 3

C
1 : 2

D
1 : 1

Solution

Power ratings are always added irrespective of whether the resistances are connected in series or in parallel. Hence,