# Physics power question frustrating me

## Homework Statement

Two bulbs P and Q labelled 12V , 24 W and 12 V and 36 W respectively are connected in series with a battery 24 V . Among the following statements , which one describes correctly about bulb P and Q

(a) potential difference across P > pd across Q

(b) resistance of Q > resistacne of P

(c) current passing through Q > current in P

(d) power dissipated from Q > power dissipated from P

(e) potential difference and current in both bulbs are the same

## The Attempt at a Solution

For (a) , i don think its right , since from P=VI , where I is constant here , when P increases ,V also increases .

For (b) , i think its correct because from P=I^2 R , when P increases , R also increases .

(c) its not correct since the current passing through both bulbs are the same

(d) this is also correct , since given that Q is 36 W and P is 24 W

(e) this is incorrect .

Is my reasoning for each correct ?

kuruman
Homework Helper
Gold Member

What does one mean when one says "a light bulb is labeled 12 V and 24 W"? What information can be extracted from this?

What does one mean when one says "a light bulb is labeled 12 V and 24 W"? What information can be extracted from this?

the potential difference across it is simply 12 V and the power it requires to light is 24 W , is it that simple ? And also the current is 2 A .

kuruman
Homework Helper
Gold Member

Not quite. A light bulb will give some light even if the applied voltage is less than the rated voltage. It means that when 12 V is applied to the bulb, the power dissipated in it will be 24 W. Can you use this information to find the resistance of the bulb?

Not quite. A light bulb will give some light even if the applied voltage is less than the rated voltage. It means that when 12 V is applied to the bulb, the power dissipated in it will be 24 W. Can you use this information to find the resistance of the bulb?

oh , yeah , P=V^2/R so when the power dissipated from the bulb is higher when the same amount of voltage is supplied to the bulb , the resistance will be higher .

so (b),(e), (c) are out .

is (d) correct ?

kuruman
Homework Helper
Gold Member

Why don't you calculate the power dissipated in each resistor and answer your own question?

Why don't you calculate the power dissipated in each resistor and answer your own question?

ok , thank you for your help .