1 Find the current through
a resistor of 20 Ω if the potential difference across it is 0.5 V.
I = V/R = 0.5/20
= 0.025A = 25mA
2 When a p.d. of 2 V is
applied across a resistor the current is 0.1 A. What is the value of the
resistor? R= V/I = 2/0.1 = 20 Ω
3 A p.d. of 100 V is applied across a resistor of 2 kΩ.
What is the current?
I = V/R = 100/2000 = 0.05A
4 What p.d, will produce a
current of 2 mA through a resistor of 4 kΩ?
V = I R = 0.002 x
4000 = 8V
5 Find the value of a resistor if a p.d. of 2 V produces a
current of 0.5 μA.
R = V/I = 2/0.5 x10-6 = 4000000 = 4MΩ
6 Find the current through a 1.5 MΩ resistor when a p.d.
of 4.5 V is applied.
I = V/R = 4.5/1.5 x106 = 3 x 10-6A
7 A lamp operated by a 240 V supply takes a current of
0.625 A. Find the resistance of the lamp.
R = V/I = 240 /0.625 = 384 Ω
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, what length of wire is in the coil?
R = V/I = 4.5/ 0.75 = 6 Ω
Length = 6 Ω/1.5 Ωm-1 = 4m
