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Date November 2020 Marks available 3 Reference code 20N.2.SL.TZ0.5
Level Standard level Paper Paper 2 Time zone 0 - no time zone
Command term Determine Question number 5 Adapted from N/A

Question

The graph shows how current I varies with potential difference V across a component X.

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 20mA.

Component X and the cell are now placed in a potential divider circuit.

 

Outline why component X is considered non-ohmic.

[1]
a.

Determine the resistance of the variable resistor.

[3]
b(i).

Calculate the power dissipated in the circuit.

[1]
b(ii).

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]
c(i).

Describe, by reference to your answer for (c)(i), the advantage of the potential divider arrangement over the arrangement in (b).

[2]
c(ii).

Markscheme

current is not «directly» proportional to the potential difference
OR
resistance of X is not constant
OR
resistance of X changes «with current/voltage»

a.

ALTERNATIVE 1

voltage across X=2.3«V»

voltage across R«=4.0-2.3»=1.7«V»

resistance of variable resistor «=1.70.020»=85«Ω» ✓

 

ALTERNATIVE 2

overall resistance «=4.00.020»=200«Ω» ✓

resistance of X «=2.30.020»=115«Ω» ✓

resistance of variable resistor «=200-115»=85«Ω» ✓

b(i).

power «=4.0×0.020»=0.080«W» 

b(ii).

from 0 to 60mA

c(i).

allows zero current through component X / potential divider arrangement

provides greater range «of current through component X»

c(ii).

Examiners report

[N/A]
a.
[N/A]
b(i).
[N/A]
b(ii).
[N/A]
c(i).
[N/A]
c(ii).

Syllabus sections

Core » Topic 5: Electricity and magnetism » 5.2 – Heating effect of electric currents
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