H214 Current of Electricity

Question 1

Define electric curent

Answer 1

Electric current is the rate of flow of charge

Question 2

What is the formula of electric current?

Answer 2

I = Q/T

Question 3

For a current I in a wire that causes the charge carriers to have a drift velocity v, derive an equation relating current to the number density of charge carriers in the wire n, the cross-sectional area of the wire A and the charge on each charge carrier q.

Answer 3

For a wire segment of length L, total charge in this volume is:
Q = (number of charge carriers in volume)(q)
= n(volume)q
=nALq

Time taken, t, for charge carriers to have net displacement of L:
L = v/t

Current is the rate of flow of charge:
I = Q/t
I = nALq / L/v
= nAvq

Question 4

What is the formula for the drift velocity of a current-carrying conductor?

Answer 4

I = nAvq

I: current (A)
n: number density of charge carriers
A: cross-sectional area
V: drift velocity
q: charge

Question 5

Define electromotive force.

Answer 5

Electromotive force (emf) the energy transformed from chemical to electrical per unit charge when charge is driven round a complete circuit.

Question 6

Define potential difference.

Answer 6

Potential difference is the energy transformed from electrical to other forms per unit charge when charge passes through an electrical component.

Question 7

What is the formula for potential difference?

Answer 7

V = W/Q

Question 8

State the formulas relating power output of electrical component.

Answer 8

P = IV
= I^2R
= V^2/R

Question 9

State the formulas relating power output of electrical component.

Answer 9

P = Iemf
= I^2R
= emf^2/R

Question 10

Define resistance.

Answer 10

Resistance is the ratio of potential difference across a component to the current passing through it.