4.1 Charge And Current

Question 1

What is electric current? State it’s 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

Q=IT
Q, charge (coulombs)
I, current (amps)
T, time (seconds)

Question 3

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

Answer 3

e is the elementary charge
units are coulombs

Question 4

Give two examples of possible charger carriers

Answer 4

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

Question 5

True or false current flows from negative to positive

Answer 5

False
Conventional current is the ‘flow of positive charge’-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

You can measure the current in a circuit with an 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
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=Anev
I=current
A=cross-sectional area
n= number density of charge carriers
e=elementary charge
v=mean drift velocity

Question 10

What are the units of ‘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

conductors, semiconductors, insulators