'A Level' Questions on Characteristic Curves - Filament Lamp
Q1.
In an attempt to investigate how the resistance of a filament lamp varies with current through the lamp, a student obtains the results shown in the table below
voltage /V |
0.50 |
1.50 |
3.00 |
4.50 |
6.00 |
12.00 |
current /A |
0.51 |
1.25 |
2.00 |
2.55 |
2.95 |
4.00 |
resistance /![](../../../../graphics/symbols/omega.gif) |
0.98 |
1.20 |
1.50 |
1.76 |
2.03 |
3.00 |
(a) Complete the table by calculating the corresponding values of resistance.
[deduct one mark for each incorrect value]
(2 marks)
(b)
(i) On an A4 sheet of graph paper plot a graph of resistance against current for the filament lamp.
![](Q1.png)
-
sensible scales chosen ![](../../../../graphics/symbols/nuclides/ticksmall.png)
-
points plotted correctly [deduct one mark for each mistake] ![](../../../../graphics/symbols/nuclides/ticksmall.png)
![](../../../../graphics/symbols/nuclides/ticksmall.png)
-
line of best fit (smooth curve NOT dot to dot line!) ![](../../../../graphics/symbols/nuclides/ticksmall.png)
(ii) Use your graph to estimate the resistance of the filament lamp when no current flows through the lamp.
0.90 ![](../../../../graphics/symbols/omega_red.png)
![](../../../../graphics/symbols/nuclides/ticksmall.png)
(iii) Use your graph to determine the change in the resistance of the filament when the current increases:
0.22 ![z](../../../../graphics/symbols/omega_red.png)
![z](../../../../graphics/symbols/nuclides/ticksmall.png)
0.38 ![z](../../../../graphics/symbols/omega_red.png)
![z](../../../../graphics/symbols/nuclides/ticksmall.png)
(iv) Calculate the power dissipated in the lamp filament when the current through the filament is 1.0 A and 2.0 A.
1.0 A :
1.12 W ![z](../../../../graphics/symbols/nuclides/ticksmall.png)
and 2.0 A:
6.0 W ![z](../../../../graphics/symbols/nuclides/ticksmall.png)
(8 marks maximum)
(c) Using information from part (b)(iv), explain why the change in resistance of the filament is less for a current change of 0 to 1.0 A than for a current change of 1.0 A to 2.0 A. Do not attempt any calculation.
Resistance increases with increasing temperature
The
increase in heat dissipation for 1.0 A to 2.0 A is greater than for 0 to 1.0 A
and so there is a greater corresponding rise in temperature ![z](../../../../graphics/symbols/nuclides/ticksmall.png)
(2 marks MAX)
(Total 12 marks)