# Simple Circuits Problem

• Engineering

## Homework Statement

Determine the energy required to move 260C through 6V.

q = Cv
U = (1/2)*C*v^2

## The Attempt at a Solution

C = q/v = 260C/6V = 130/3 F
U = (1/2)(130/3 F)(6V)^2 = 780J

I applied the voltage/charge relationship and energy equation for a capacitor because they seemed to be the only equations that made sense with the given values, but I'm not certain this is correct. If someone could let me know if I'm going about this correctly it would be appreciated. Thanks.

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## Answers and Replies

I think you need the formula:

$$V = \frac{W}{Q}$$

where V = volts, W = work(energy or joules), and Q = coulombs

I think you need the formula:

$$V = \frac{W}{Q}$$

where V = volts, W = work(energy or joules), and Q = coulombs

It seems the units don't work out for that formula.

Did you mean V = W/I? If so I think it doesn't help for this problem since I don't know the current and can't find the current from the given values.

Ok, I see where I went wrong. I was looking at the variable W as if it had the unit of watts, which in power, not energy. I now see that W is energy is joules, and the formula you wrote does work. Thanks Number2Pencil, I think I can solve the problem now.

Ok, I see where I went wrong. I was looking at the variable W as if it had the unit of watts, which in power, not energy. I now see that W is energy is joules, and the formula you wrote does work. Thanks Number2Pencil, I think I can solve the problem now.

A Watt is a Joule/second, if you did the calculation having used Joules in place of Watts, I'd recommend going back and checking your solution over again

I think the variable W and W as the symbol for watt caused confusion. So the correct answer would be:

Energy = Charge*Potential = 260C*6V = 1560J

Right?

It looks like your going to have to derrive an equasion
Try V=E/Q=W/Q..... I=Q/t..... E=VIt... and Q=Ne

V = voltage in volts E= energy in joules Q= charge W= work in joules I= current in amps N= number of electrons e = electron constant t=time

berkeman
Mentor
I think the variable W and W as the symbol for watt caused confusion. So the correct answer would be:

Energy = Charge*Potential = 260C*6V = 1560J

Right?

Correct, Steve. Yeah, using W for both work and Watts can cause confusion.