# Power Increase In Rheostat Problem

Discussion in 'Electronics Homework Help' started by BlueScreen, Jul 22, 2012.

1. ### BlueScreen

4
0
Jul 22, 2012
Hello All,
Im self studying Electronics at home, and I at the moment on Ohms Law.
Now I have a problem:
"What is the increase in current when 15v is applied to 10,000 ohm rheostat, which is adjusted to 1000 ohm value?"
Now I have worked out that the power through the Rheostat is:
a. 0.015A at 1000 ohms, and
b. 0.0015A at 10,000 ohms.
But Im stuck on the power increase. It looks like ten percent, but I could be wrong.

Any clues?

Cheers
Glenn.

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,411
2,779
Jan 21, 2010
I^2R or VI

Work it out for both.

3. ### BlueScreen

4
0
Jul 22, 2012
I will thanks Steve.

4. ### Laplace

1,252
184
Apr 4, 2010
Are you using the terms 'power' and 'current' interchangeably? They are not the same thing.

If a value changes for example from 0.0002 to 0.002 then that is not a change of 10% but rather a factor of ten, i.e., 1000%

5. ### BlueScreen

4
0
Jul 22, 2012
No, im not. Im aware of the power formula and im just using Ohm's Law for the questions (cause thats what the questions are).
I shouldnt have written 'power increase', my error. Im just wanting to know the increase in current. Its been a long long time since school and I have forgotten how to work out the increase.

I guess the disadvantage of self study is that I don't have a teacher to ask the next day.
But, in retrospect, when I was at school we didnt have the internet to turn to.

6. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,411
2,779
Jan 21, 2010
If you calculate two values and you want to now the % change from first to second, the correct formula is:

(second - first * 100) / first