Date | May 2017 | Marks available | 2 | Reference code | 17M.3.SL.TZ2.2 |
Level | Standard level | Paper | Paper 3 | Time zone | Time zone 2 |
Command term | Explain | Question number | 2 | Adapted from | N/A |
Question
The circuit shown may be used to measure the internal resistance of a cell.
The ammeter used in the experiment in (b) is an analogue meter. The student takes measurements without checking for a “zero error” on the ammeter.
An ammeter and a voltmeter are connected in the circuit. Label the ammeter with the letter A and the voltmeter with the letter V.
In one experiment a student obtains the following graph showing the variation with current I of the potential difference V across the cell.
Using the graph, determine the best estimate of the internal resistance of the cell.
State what is meant by a zero error.
After taking measurements the student observes that the ammeter has a positive zero error. Explain what effect, if any, this zero error will have on the calculated value of the internal resistance in (b).
Markscheme
correct labelling of both instruments
[1 mark]
V = E – Ir
large triangle to find gradient and correct read-offs from the line
OR
use of intercept E = 1.5 V and another correct data point
internal resistance = 0.60 Ω
For MP1 – do not award if only \(R = \frac{V}{I}\) is used.
For MP2 points at least 1A apart must be used.
For MP3 accept final answers in the range of 0.55 Ω to 0.65 Ω.
[3 marks]
a non-zero reading when a zero reading is expected/no current is flowing
OR
a calibration error
OWTTE
Do not accept just “systematic error”.
[1 mark]
the error causes «all» measurements to be high/different/incorrect
effect on calculations/gradient will cancel out
OR
effect is that value for r is unchanged
Award [1 max] for statement of “no effect” without valid argument.
OWTTE
[2 marks]