DC circuits

[cseet]

Hi all,

I really need somebody to explain to me how to work the following problem...

Q:
A 1.50E2 - W heater is designed to operate with an EMF of 120V. If the potential difference across the heater changes by a small amount such as 2.6%, approximately by what factor does the power change? (Hint: approximately the changes with differentials) (unit %).

can somebody kindly explain to to go about it?? thanks
cseet

[Doc Al]

The first step is to express the power as a function of voltage. That should be easy. Then you have P = f(V).

Then you approximate the changes as follows:

ΔP = f'(V)ΔV

You can then manipulate this equation to give you the relationship between ΔP/P and ΔV/V. Give it a try.