8.1

(Maximum) energy provided (work done) by a battery per coulomb/unit charge passing through it.
Tips:
 EMF is the maximum energy provided by a battery per unit of charge passing through it.
 Distinguishing potential difference from EMF is key for students. Potential difference measures the work required to move charges between points due to resistance, while emf represents the conversion of chemical energy to electrical energy.

2 marks
(1 x 2 marks)

8.2

13V
Tip: the initial potential difference across the terminals of the battery is the EMF because the switch is initially open.

1 mark

8.3.1

^{(1)}
^{(2)}
^{(3)}
Tip: given the resistor's 5,6 Ω resistance and the 10,5 V of the external potential difference across it, you can use Ohm's law to calculate the current.

3 marks
(3 x 1 mark)
Marking criteria:
 ^{(1) }Appropriate formula
 ^{(2) }Whole substitution
 ^{(3) }Final answer:1,88A

8.3.2

Option 1
Or
Option 2
Or
Option 3
Tips:
 There are many different equations for calculating power, providing a variety of methods to determine the value.
 Remember to include units with your answer.

3 marks
(3 x 1 mark)

8.3.3

Option 1
Or
Option 2
Or
Option 3
Tip: the answer can be easily reached by direct substitution into the formula given on your formula sheet.

3 marks
(3 x 1 mark)

8.4.1

Decreases
V_{internal resistance}/internal volts increase
Tips:
 Adding a resistor or pair of resistors in series will decrease the total resistance of the circuit, this decrease in resistance will increase the current (as given by the fact that the ammeter reading increases to 4A).
 The increase in current will increase the lost volts (V_{lost} = Ir) which will in turn decrease the reading on the voltmeter (emf = V_{ext }+ V_{lost}).

2 marks
(2 x 1 mark)

8.4.2

How to approach this question:
 The emf and internal resistance remain the same, the current is given as 4A. These values can be used to calculate the external resistance.
Option 1
^{(1)}
^{(2)}
 The total effective resistance of the parallel resistors is 1,94 Ω and the bottom branch is 5,6 Ω.
^{(3)}
 By halving the value of the combined resistance of the two identical resistors, each of resistance X, you can calculate X.
^{(4)}
^{(5)}
There are more ways to answer this question. To view other options, click here.

5 marks
(5 x 1 mark)
Marking criteria:
 ^{(1) }Formula Ɛ = I(R + r)
 ^{(2) }Correct substitution into Ɛ = I(R + r)
 ^{(3) }Substitution of values into the Rp formula
 ^{(4) }Halving value of R_{2x }
 ^{(5) }Final answer: 1,49
 Range: 1,46 Ω – 1,49 Ω
