Question

In the circuit given below :
a)- Would any bulb glow when plug key is in open position ?
b)- Write the order of brightness of the bulb when key is closed. Give reason.

Answer 1

a) No, none of the bulbs will glow, 'cause it would be an open circuit.
b) As in series, the current remains constant, so,

P = I² R

for each bulb, I² is constant, So, More power means more Resistance.

Hence order of glow of bulbs will be,

In the direction of conventional current, Increasing order.

Answer 2

Given:

3 bulbs with rating = 25W , 40W, 60W

Voltage = 6V

Ammeter

To Find:

• Would any bulb glow when plug key is in open position
• order of brightness of the bulb when key is closed

Solution:

from the Figure,

it is clear that if the key is open then the connection is not completed so current will not flow and no bulb will glow.

Now,

if the key is closed then the current will start to flow so the bulb will glow

now the order of glow of the bulb will be 60W > 40W > 25W

since P = V I

here all are in series connection so the current is constant.

P ∝ V

more the voltage more the power more the glow.

So, Order of glow will be 60W > 40W > 25W.