2 or 3 questions (power dissipating, newton and potencial)

Hello people !

I'm doing an homework in maths and there's some questions that are in relations with what we learn in the electro class. But some of the questions I need to work on were not covered in my electric class so far (we had a day canceled).

I am not asking for straight answers but I'm gonna write the 3 questions that bother me anyway, so I'll be able to ask my questions. (We are in DC).


1. A power (P) of 320mW is dissipated in a resistor (R) of 200 ohms. What is the potencial (in volts) at the terminals of the resistor ?

2. What energy is needed to move a charge of 4,0 mC under a potencial of 60,0V ? (Significant numbers)

3. With the significant numbers:
a) what is the potencial of a resistor knowing that its ohmic value is 15,0 Ω and the current in the circuit is 0,40 A.

b) determine the enegy dissipated in the resistor in one minute.

So now, my questions !

in 1., do I need to use √(WR) ?
like it'd be square of (0,320W times 200 Ω) = 64 volts
?


in the 2nd one. (I'll sleep on this one and try it in the morning)

Finally the 3rd one, a) is it simply V=RI (so 6 volts because 15Ω x 0.4 A) ?

but here's the one bothering me: energy dissipated in the resistor in one minute, I need an explanation on this one if someone has some time to teach this here !

A big thank you, I hope all the blabla I wrote is readable and understandable! My english is hard to reach tonight, I'm weary and need a bit of sleep.
²

1. Yes, P=V²/R. So V=√(PR).

3a. Yes.
3b. Power = I²Rt Joules. Where t = seconds.

Mike.

My replies in RED

ElectroNewby said:

in 1., do I need to use √(WR) ? Yes
like it'd be square of (0,320W times 200 Ω) = 64 volts? Your numbers are wrong and I think you mean square root.



in the 2nd one. (I'll sleep on this one and try it in the morning) Good because I have no idea what the question means!

Finally the 3rd one, a) is it simply V=RI (so 6 volts because 15Ω x 0.4 A) ? Yes

but here's the one bothering me: energy dissipated in the resistor in one minute, I need an explanation on this one if someone has some time to teach this here !

Energy is measured in Joules.
A Joule is a watt.second, so 5 watts for 3 seconds is 15 Joules.
Does that help?

Click to expand...

Thank you gentlemen, and good morning.

So the 2nd question was "What energy is needed to move a charge of 4,0 mC under a potencial of 60,0V ? (Significant numbers)"

I think I should have written "significant figures" (which is something about the decimals I believe). I need to find the energy needed in order to move a charge of 4 milliCoulomd when a supply is set to 60 volts.

This is a harsh one.

*also, I forgot to square root my 64 in my previous post, so I meant 8 volts.

I did V=W/Q

So 60 Volts = ?/0,004 coulomb
so W = VxQ
so 0.24 Watts = 60V x 0.004 C

Is this correct ?

P = W(joules)/Q(coulomb) -> can I assume that joules = watts and coulomb = amperes right away if there's no time factor ?

I'm guessing that 4millicoulomb requires 4mA for 1 second. Hence at 60V it would require 240mJ. But it is only a guess.

Mike.