The questions are on the ohm's law test. Take it under real conditions before reading the mark scheme.
Quick answer: Current is the flow of charge in amperes, potential difference is the energy per coulomb in volts, and resistance in ohms is the opposition to current. This mark scheme gives the model answers and the marks for the 8 questions of the Physics 9-10 test on ohm's law, from definitions to longer wire, with the equivalent answers to accept.
The model answers include mark allocations. Accept equivalent wording, and give error carried forward when a wrong earlier answer is used correctly in a later part.
Level: Physics grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: GCSE P2, IGCSE 4.3
Question 1 Definitions (2 marks)
- R = V ÷ I
- One joule of energy is transferred for each coulomb of charge that passes (1 V = 1 J/C).
Marking: 1 mark each.
Question 2 Using V = I R (3 marks)
- R = V ÷ I = 7.5 ÷ 0.050 = 150 Ω
- V = I R = 0.080 × 150 = 12 V
Marking: 1 mark for the equation or substitution; 1 mark for the answer; 1 mark for part (b).
Question 3 Measuring resistance (3 marks)
- The ammeter is placed in series with R in the loop; the voltmeter is placed in parallel across R only.
- R = V ÷ I
Marking: 1 mark for the ammeter in series; 1 mark for the voltmeter across R; 1 mark for the equation.
Question 4 Filament lamp (3 marks)
The decreasing gradient means that the current rises less for each extra volt, so the resistance increases. The filament becomes hotter as the current increases, so its ions vibrate more and collide with the electrons more often.
Marking: 1 mark for resistance increases; 1 mark for hotter filament; 1 mark for more collisions with electrons.
Question 5 Sensors (3 marks)
- The resistance decreases.
- Put the thermistor in a circuit with the fan. When the temperature rises, the thermistor resistance falls, so the current increases and switches on the fan.
Marking: (a) 1 mark. (b) 1 mark for resistance falling as temperature rises; 1 mark for the current rising and switching on the fan.
Question 6 Energy transferred (2 marks)
W = Q × V = 25 × 12 = 300 J
Marking: 1 mark for the equation or substitution; 1 mark for the answer with unit.
Question 7 Diode (2 marks)
It lets current pass in one direction only. Use: converting alternating current to direct current, or protecting a circuit against a reversed battery.
Marking: 1 mark for the one-way statement; 1 mark for a use.
Question 8 Longer wire (2 marks)
R = 12 Ω. Charge has twice as far to travel through the metal, so there are twice as many collisions and the resistance doubles.
Marking: 1 mark for 12 Ω; 1 mark for the explanation.
