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AQA A-level Physics Uncertainty and Error Mark Scheme
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- AQA
Mark Scheme for the corresponding document: 'AQA A-level Physics Uncertainty and Error'.
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theonlinephysicstutor.comMark schemes
(a) (i) Voltmeter across terminals with nothing else connected to battery / no additional load.
1
✓
1
(ii) This will give zero / virtually no current ✓
1
(b) (i)
Answer must clearly show power: εI and VI, with I cancelling out to give
formula stated in the question ✓
1
(ii) Voltmeter connected across cell terminals ✓
Switch open, voltmeter records ε
Switch closed, voltmeter records V
Both statements required for mark ✓
Candidates who put the voltmeter in the wrong place can still
achieve the second mark providing they give a detailed description
which makes it clear that:
To measure emf, the voltmeter should be placed across the cell with
the external resistor disconnected
And
To measure V, the voltmeter should be connected across the
external resistor when a current is being supplied by the cell
2
(c) Vary external resistor and measure new value of V, for at least 7 different values of
external resistor ✓
Precautions - switch off between readings / take repeat readings (to check that emf or
internal resistance not changed significantly) ✓
2
(d) Efficiency increases as external resistance increases ✓
Explanation
Efficiency = Power in R / total power generated
I2R / I2(R + r) = R / (R + r)
So as R increases the ratio becomes larger or ratio of power in load to power in
internal resistance increases ✓
Explanation in terms of V and ε is acceptable
2
[9]
(a) 2.9% ✓
2
Allow 3%
1
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(b) seen ✓
1
0.29 mm or 2.9 x 10-4 m✓ must see 2 sf only
1
(c) ± 0.01 mm ✓
1
(d) Clear indication that at least 10 spaces have been measured to give a spacing = 5.24
mm✓
spacing from at least 10 spaces
Allow answer within range ±0.05
1
(e) Substitution in d sinθ = nλ✓
The 25 spaces could appear here as n with sin θ as 0..5
1
d = 0.300 x 10-3 m so
number of lines = 3.34 x103✓
Condone error in powers of 10 in substitution
Allow ecf from 1-4 value of spacing
1
(f) Calculates % difference (4.6%) ✓
1
and makes judgement concerning agreement ✓
Allow ecf from 1-5 value
1
(g) care not to look directly into the laser beam✓
OR
care to avoid possibility of reflected laser beam ✓
OR
warning signs that laser is in use outside the laboratory✓
ANY ONE
1
[10]
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Page 23 of 30
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