Student A investigated how the current in resistor R at constant temperature varied with the potential difference across the resistor.
Student A recorded both positive and negative values of current.
Figure 2 shows the circuit Student A used.
i- Describe a method that Student A could use for this investigation.
[6 marks]
ANSWER
Record current passing through a resistor R using ammeter.
Record voltage across R using voltmeter.
Varry the current using variable resistor.
Ensure low current are used
Reversing polarity of battery results in positive and negative readings
Turn off circuits in between readings using switch
ii- Student B repeated the investigation.
During Student B’s investigation the temperature of resistor R increased.
Explain how the increased temperature of resistor R would have affected Student B’s results.
[2 marks]
ANSWER
The current would not directly proportional to the p.d anymore.
The current and p.d. graph will not be a straight line.
(The linear and direct relationship between current and potential difference exist only when the temperature of the resistor is kept constant. Once the temperature increases, the resistance increases, and graph of current vs p.d. is curved.)
iii- What is the resolution of the moving coil ammeter?
[1 mark]
ANSWER
0.2 A
(Resolution is the least possible value that the instrument can detect, which means it is the smallest division that the instrument has. So in this case it is 0.2 A.)
iv- Student B replaced the moving coil ammeter with a digital ammeter.
Figure 4 shows the reading on the digital ammeter.
The digital ammeter has a higher resolution than the moving coil ammeter.
Give one other reason why it would have been better to use the digital ammeter throughout this investigation.
[1 mark]
ANSWER
There will be no parallax error.
This wil give more accurate reading or nearest to the true value.
Always remember, one of the basic advantages of digital instruments is that they give more precise and exact reading, and is also easier to read as there is no chance of parallax error.
