Question

mangal room heater is marked as 1000w-200v.find the percentage change in the power of heater if voltage drops to 160v​

Answer 1

P=VI

SO, 1000=200*I

Therefore, I=5A

Now, power for V=160

Where I=5A

So,P=VI

P=160*5=800W

Difference =200W

Percentage=200/1000*100

=20% answer

Answer 2

Answer:

Percentage change in power of heater is equal to 36% if voltage falls from $200V$ to $160V$.

Explanation:

Case-I: When power of heater $P=1000w$ and voltage $V=200Volt$

Here, Resistance of heater, $R=\frac{V^{2}}{P}$

⇒   $R=\frac{(200)^{2}}{1000}$

⇒    $R=\frac{40000}{1000}$

∴   $R=40$Ω

Case-II: When the voltage falls from 200V to 160V

Then Power, $P=\frac{(V)^{2}}{R}$

⇒  $P=\frac{(160)^{2}}{40}$

∴    $P=640W$        

Change in power of heater, $=1000W-640W=360W$

Percentage change % in power  $=\frac{360}{1000}*100$ $=36$%