Current Electricity — Practice

Question 1

A 2 m copper wire of area 0.5 mm^2 has resistivity 1.7e-8 ohm m. Find its resistance.

Accepted Answer

R = rho L/A = 1.7e-8 x 2 / 0.5e-6 = 0.068 ohm.

Question 2

Find the current through a 10 ohm resistor connected to a 12 V battery of internal resistance 2 ohm.

Accepted Answer

I = E/(R + r) = 12/(10 + 2) = 1 A.

Question 3

In a Wheatstone bridge R1 = 2, R2 = 4, R3 = 3 ohm. Find R4 for balance.

Accepted Answer

R1/R2 = R3/R4 gives 2/4 = 3/R4, so R4 = 6 ohm.

Question 4

A potentiometer wire of length 10 m and resistance 20 ohm is driven by a 2 V cell. Find the potential gradient.

Accepted Answer

Current I = 2/20 = 0.1 A. Potential gradient = IR/L = (0.1 x 20)/10 = 0.2 V/m.

Question 5

Two cells E1 = 6 V (r1 = 1) and E2 = 4 V (r2 = 1) oppose across R = 2 ohm in a loop. Find the current.

Accepted Answer

KVL: 6 - I(1) - I(2) - I(1) - 4 = 0, so 2 - 4I = 0 and I = 0.5 A.

Practice — Current Electricity