Question

[U.P.S.C.L.E.S. E.T.E.-I, 2013]
1. A 12 V automobile light is rated at 30 W. The total charge that
flows through the filament in one minute is
(a) 30C (b) 12 C (c) 150 C (d) 180 C
explanation??? ​

Answer 1

Given : A 12 V automobile light is rated at 30 W.

To find : The total charge that flows through the filament in one minute is ...

solution : power dissipation through automobile light is given by, P = Vi

here P = 30W , V = 12 volts

so, i = 30/12 = 10/4 = 2.5 Ampere.

we know, current is the charge flows through a wire in a specific time. in short, current is the ratio of charge flows through wire to time taken.

so, i = Q/t

here i = 2.5 A , t = 1 min = 60 sec

so, Q = it = 2.5 A × 60 sec = 150 C

Therefore the total charge that flows through the filament in one minute is 150 C. i.e., option (C) is correct choice.

Answer 2

Given ,

• Potential difference (v) = 12 v
• Power (P) = 30 w

We know that ,

$\large \boxed{ \sf{P = VI }}$

Thus ,

30 = 12 × I

I = 30/12

I = 2.5 amp

Therefore ,

The current is 2.5 amp

Now ,

$\boxed{ \sf{Current \: (I) = \frac{q}{t} }}$

Thus ,

2.5 = q/60

q = 2.5 × 60

q = 150 coulomb

Therefore ,

The total charge that flows through the filament in one minute is 150 C