4.1 Charge and Current

Question 1

What is electric current? state units

Answer 1

The rate of flow of charge. It is measured in Amps

Question 2

Give the symbol equation relating charge, current and time (include units)

Answer 2

I = ΔQ / Δt

Q = charge, coulombs
I = current, amps
t = time, seconds
Δ = change

Question 3

In electricity what does ‘e’ represent? what are the units?

Answer 3

e is the elementary charge, coulombs

Question 4

Give two examples of possible charge carriers

Answer 4

electrons - in metals
ions - in electrolytes (aqueous solutions)

Question 5

T or F: Conventional current flows from negative to positive

Answer 5

False
Conventional current is the flow of positive charge so it is in the opposite direction to the movement of the electrons in the circuit

Question 6

How can you measure the current in a circuit?

Answer 6

ammeter connected in series with the component

Question 7

What is Kirchhoff’s first law?

Answer 7

All of the current going into a junction is equal to the current leaving the junction ie charge is conserved

Question 8

What is meant by ‘mean drift velocity’

Answer 8

The average velocity of the charge carriers due to the applied electric field. It has to be an average because they’re often moving randomly in all directions

Question 9

What equation uses the drift velocity to calculate current?

Answer 9

I = nAve

I = current
n = number density of charge carriers
A = cross sectional area of conductor
v = mean drift velocity
e = elementary charge

Question 10

What are the units for ‘ number density of charge carriers’ in the equation relating current and drift velocity?

Answer 10

m^-3

Question 11

Put conductors, semiconductors and insulators in order from highest ‘n’ (number density of charge carriers) to lowest

Answer 11

highest:
conductors
semiconductors
insulatord
lowest: