Topic Menu

Cyber-chess a chess instruction site

GCSE Standard Questions: Electric Circuits

Q14.

(a) Chloe investigated how the current in resistor R varied box with the potential difference across the resistor. She maintained a constant temperature for the resistor throughout the experiment.

She recorded both positive and negative values of current in her notebook.

Here is the circuit Chloe used:

Describe a method that Chloe could have used for this investigation.

[6 marks]

This type of question is marked in two ways:

- the examiner looks for relevant points

- but also for a logical sequence...

It is not just a 'tick fest' - but a marker does look to see how many relevant points you have made, then considers how you have strung them together to put your answer into a 'level'

Level 3:

The method would lead to the production of a valid outcome.

All key steps are identified and logically sequenced.
5 - 6 marks
Level 2:

The method would not necessarily lead to a valid outcome.

Most steps are identified, but the plan is not fully logically sequenced.
3 - 4 marks
Level 1:

The method would not lead to a valid outcome.

Some relevant steps are identified, but links are not made clear.
1 - 2 marks
Level 0:

No relevant content
0 marks

 

Indicative content:

measure the current flowing through R using the ammeter

measure the p.d. across R using the voltmeter

vary the resistance of the variable resistor (or vary the number of cells or use a variable power supply)

record a range of values of current and p.d. in your notebook

ensure current is kept low to avoid temperature increases

switch circuit off between readings to minimise temperature increases

reverse the connection of R to power supply and repeat measurements of I and V in negative direction

plot a graph of current against p.d

(b) Lois repeated the investigation.

During Lois's investigation the temperature of resistor R increased.

Explain how the increased temperature of resistor R would have affected Lois's results.

The current and p.d. would not be directly proportional when she plotted the graph. Therefore her I-V graph would not be a straight line, it would be curved because resistance of R would increase at higher temperatures not remain constant.

[2 marks]

(c) The diagram shows the scale on the analogue moving coil ammeter Chloe used, at one time in the investigation.

(i) What is the resolution of the moving coil ammeter? 0.2 A

(ii) What value of the current is shown by the meter? 1.3 A

You can read an analogue meter to the nearest half a division - in this case the pointer is over half way between 1.2 A and 1.4 A, but nearer to the midpoint than to the 1.4 A marker - so you would record this as 1.3 A.

[2 marks]

(d) Lois replaced the moving coil ammeter with a digital ammeter.

The diagram shows a reading on the digital ammeter.

The digital ammeter has a higher resolution than the moving coil ammeter.

(i) What is the resolution on the digital ammeter? 0.01 A

(ii) Give a reason other than resolution why it would have been better to use the digital ammeter throughout this investigation.

There is less chance of misreading the meter as you do not have to worry about parallax errors and ensuring you were viewing the meter from the correct angle.

If you said it was 'easier' or 'quicker' to read, or avoided human error the examiners gave you no marks.

[2 marks]

(Total 12 marks)