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 /	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.

sensible scales chosen

points plotted correctly [deduct one mark for each mistake]

line of best fit (smooth curve NOT dot to dot line!)

(ii) Use your graph to estimate the resistance of the filament lamp when no current flows through the lamp.

0.90

(iii) Use your graph to determine the change in the resistance of the filament when the current increases:

from 0 to 1.0 A - 0.22

from 1.0 A to 2.0 A - 0.38

(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

and

2.0 A: 6.0 W

(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

(2 marks MAX)

(Total 12 marks)