Ohm's Law

I ampere = I A

I milliamp = I mA 1/1000 A = 10^-3A.

I microamp = I μA = 1/1 000 000 A =10^-6 A

I volt = I V

I kilovolt = I kV =1000 V =10³ V

I millivolt = I mV = 1/1000 V = 10³ V

1 ohm = 1Ω

1 kilohm = 1KΩ =10³ kΩ

1 megohm = 1 MΩ = 1 000 000 Ω = 10⁶Ω

Find the potential difference needed to send a current of 2 μA through a resistor of 4 kΩ

V=IR V = p.d. in V

I = current in A = 2μA = 2 x 10^-6A

R = resistance in Ω = 4kΩ = 4000Ω

V = 2 x 10^-6 x 4000

= 8 X 10^-3 V or 8 mV

1 Calculate the current through a resistor of 20 Ω if the potential difference across it is 0.5 V.

2 When a p.d. of 2 V is applied across a resistor the current is 0.1 A. Calculate the value of the resistor?

3 A p.d. of 100 V is applied across a resistor of 2 kΩ. Calculate the current?

4 Calculate the p.d. that will produce a current of 2 mA through a resistor of 4 kΩ?

5 Calculate the value of a resistor if a p.d. of 2 V produces a current of 0.5 μA.

6 Calculate the current through a 1.5 MΩ resistor when a p.d. of 4.5 V is applied.

7 A lamp operated by a 240 V supply takes a current of 0.625 A. Calculate the resistance of the lamp.

8 A coil of very fine copper wire is found to take a current of 0.75 A when a p.d. of 4.5 V is applied. If the wire has a resistance of 1.5 Ω per metre, Calculate length of wire in the coil?