Question 20N.2.HL.TZ0.5
| Date | November 2020 | Marks available | [Maximum mark: 9] | Reference code | 20N.2.HL.TZ0.5 |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | Calculate, Determine, Explain, Outline, State | Question number | 5 | Adapted from | N/A |
The graph shows how current varies with potential difference across a component X.
Outline why component X is considered non-ohmic.
[1]
current is not «directly» proportional to the potential difference
OR
resistance of X is not constant
OR
resistance of X changes «with current/voltage» ✓
Most answers that didn't score simply referred to the shape of the graph without any explanation as to what this meant to the relationship between the variables.
Component X and a cell of negligible internal resistance are placed in a circuit.
A variable resistor R is connected in series with component X. The ammeter reads .
Determine the resistance of the variable resistor.
[3]
ALTERNATIVE 1
voltage across X ✓
voltage across R ✓
resistance of variable resistor ✓
ALTERNATIVE 2
overall resistance ✓
resistance of X ✓
resistance of variable resistor ✓
This question produced a mixture of answers from the 2 alternatives given in the markscheme. As a minimum, many candidates were able to score a mark for the overall resistance of the circuit.
Calculate the power dissipated in the circuit.
[1]
power ✓
A straightforward calculation question that most candidates answered correctly.
Component X and the cell are now placed in a potential divider circuit.
State the range of current that the ammeter can measure as the slider S of the potential divider is moved from Q to P.
[1]
from to ✓
Surprisingly a significant number of candidates had difficulty with this. Answers of 20 mA and 4 V were often seen.
Slider S of the potential divider is positioned so that the ammeter reads . Explain, without further calculation, any difference in the power transferred by the potential divider arrangement over the arrangement in (b).
[3]
ALTERNATIVE 1
current from the cell is greater «than » ✓
because some of the current must flow through section SQ of the potentiometer ✓
overall power greater «than in part (b)» ✓
ALTERNATIVE 2
total/overall resistance decreases ✓
because SQ and X are in parallel ✓
overall power greater «than in part (b)» ✓
Allow the reverse argument.
HL only. This question challenged candidate's ability to describe clearly the changes in an electrical circuit. It revealed many misconceptions about the nature of electrical current and potential difference, of those who did have a grasp of what was going on the explanations often missed the second point in each of the markscheme alternatives as detail was missed about where the current was flowing or what was in parallel with what.