An electric current I is given in the list of formulae on page 3 as I = Anvq.

Question 4

An electric current I is given in the list of formulae on page 3 as I = Anvq.

What do each of the symbols represent for an electric current in a metal wire?

Reference: Past Exam Paper – March 2017 Paper 12 Q32

Solution:

Answer: B.

This is a basic recall question for those who have studied about the drift speed. The formula is already available in the list of formulae on page 3, so we only need to know what each term mean.

The electric current in a metal wire is given by: I = Anvq

A is the cross-sectional area of the wire (unit: m²)

n is the number of free electrons per unit volume (unit: m^-3)

v is the average drift speed of electrons (unit: m s^-1)

q is the charge of each electron (unit: C)

Overall unit on RHS: m² m^-3 m s^-1 C = C s^-1

This is the unit of current (= charge / time)