Electricity

Question 1

Define ‘potential difference’

Answer 1

PD = Measure of energy transferred per unit charge

Question 2

Define ‘current’

Answer 2

Current = Rate of flow of charge

Question 3

Define ‘resistance’

Answer 3

Resistance = measure of how difficult it is for current to flow through a conducting material

Question 4

State Ohm’s law

Answer 4

Ohm’s law:

Current is proportional to the PD supplied

Question 5

What is an ‘Ohmic conductor’?

Answer 5

Anything that obeys Ohm’s law

Question 6

What does the Current/Voltage graph of an Ohmic Conductor look like?

Answer 6

Current is directly proportional to the PD

Question 7

Describe the relationship between current and potential difference in a filament lamp

Answer 7

• As current increases, the wire in the filament gets hotter
• Increasing its resistance
• This causes the rate of charge flow to decrease, though the same PD is being supplied.

Question 8

What is the typical resistance of an ammeter?

Answer 8

Ammeters typically have zero resistance, as they need to provide an accurate reading of the current flowing through the circuit.

Question 9

Why do batteries lose energy?

Answer 9

• Batteries have ‘internal resistance’
• Caused by electrons (charge) battery coming into contact with atoms in the battery, losing energy
• This causes less energy to be transferred between the battery and the rest of the circuit.

Question 10

State Kirchhoff’s 1st law:

Answer 10

Total current entering a junction = total current exiting a junction

Question 11

State Kirchhoff’s 2nd law:

Answer 11

Total EMF in a circuit = total PD around each component

Question 12

Explain how Kirchhoff’s 1st law affects series circuits

Answer 12

• Current in series circuits will always be the same, as there aren’t any junctions in the circuit
• The PD in the circuit will be split between components

Question 13

What is the EMF of two cells in parallel?

Answer 13

EMF = the EMF of one of the identical cells.