Im tryingto work out: Resistance= if therer are 20v and 5Av. Current= if 12v and R=3 PDS=if 3A and R=70?

Question

im not very good at science and my physics teacher is evil.
R stands for resistance in ohms.

Answer 1

V = I * R or voltage is equal to the current times the resistance.
In your first question R=20/5=4 ohms
In your second I=12/3=4 amps
In your third V= 3*70 = 210 volts

Answer 2

Your question was bit unclear, but if you are trying to calculate voltage, amps, or resistance the rule is very easy.

Voltage = Amps x Resistance.

If you have two of the three values you can calculate the third.

This formula applies for DC circuits. When you start calculating Alternating or AC circuitry, you have to calculate the reactive component if there are inductors or capacitors. Both of these have a resistance known as Impedance, which is a function of frequency. And the calculations are no longer simple arithmetic, because they have a vector component.

Answer 3

The easy way to remember the formula is just think V/IR. Just take out the one you need, and the other two give you the answer. If you want voltage, take out the V and the answer is IR. If you want current, take out the I and the answer is V/R. etc