Please help settle a disagreement...

[Brad1]

There's a 12-pack riding on this electronics math question.

The question is: "The voltage across a fixed resistance has increased by 12%. This means that the power dissipated by the resistor has increased by _____ %."

One of us says it's 25%, the other says it's 23%.

Which one is correct, and why?

Thanks,

Brad1

[J M Fahey]

1.12 x 1.12=1.2544 or 25.44% increase.

[Zipslack]

Another take...

1.12 x 1.12=1.2544 or 25.44% increase.

Assume the resistance didn't change, just the voltage. P = V^2 / R. Asssume resistance value and voltage value to play with...I'll assume 100V originally with 100 Ohms just to make things easy. (100 + 12% = 112)

P = 100*100/100 = 100 W for original

P = 112*112/100 = 125.44 W for 12% higher voltage

25.44 W difference. I like to teach my students to make up values and plug them in to see what happens...sometimes it makes more sense to them that way.

[Brad1]

Thanks guys! I don't understand what crazy numbers he was coming up with, but I got exactly the same thing you did, which I'll print out for proof.

Now all I have to do is figure out which pricey beer I'm gonna hit him up for!

Brad1

[Zipslack]

Most of 'em taste like horse-piss anyway, so go for the most expensive!

[tim]

Thanks guys! I don't understand what crazy numbers he was coming up with, but I got exactly the same thing you did, which I'll print out for proof.

Now all I have to do is figure out which pricey beer I'm gonna hit him up for!

Brad1

Would you be able to hit him up for a nice bottle of Glenfiddich "Special Reserve" instead??? :-)