A heater dissipates a power of 400 W and the potential difference across it is 110 V. If the potential difference is changed to 220 V keeping its resistance constant, what will be its power dissipation?

400 W
800 W
1600 W
cannot be determined

Question

A heater dissipates a power of 400 W and the potential difference across it is 110 V. If the potential difference is changed to 220 V keeping its resistance constant, what will be its power dissipation?

400 W
    800 W
    1600 W
    cannot be determined

anonymous · Answer

the relation between power , voltage and resistance is 
P=V² / R 
using this relation in both the cases 
P = V² / R                      -  (1)
P' =V'² / R'                        -  (2)

R=R'                            - given 
dividing (1) and (2)  we get
P  /  P'   = V²  /  V'²  
inserting the values we find 
400  / P'  =  110²  /  220²  
 
therefore P' = 800 W

anonymous · Answer

Use the formula: P = V^2 / R.

P1 = 400 W and V1 = 110 V

Since P = V^2 / R, 400 = (110^2) / R, and R = 30.25 ohms

If V2 = 220 V then P = (220^2) / 30.25 and P = 1600 W

Another method:

R1 = (V1^2) / P1  and R2 = (V2^2) / P2
where V1 = 110 V, P1 = 400 W, V2 = 220 V, and P2 is what you're trying to find.

Since R remains constant, R1 = R2 and (V1^2) / P1 = (V2^2) / P2.
(110^2) / 400 = (220^2) / P2 so P2 = 1600 W.

ANSWER: P = 1600 W.

anonymous · Answer

sorry the answer is P' = 1600 
calculation error