 # 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 / (a) Complete the table by calculating the corresponding values of resistance.

(2marks)

(b)

(i) On an A4 sheet of graph paper plot a graph of resistance against current for the filament lamp.

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

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

• from 0 to 1.0 A,
• from 1.0 A to 2.0 A

(iv) Calculate the power dissipated in the lamp filament when the current through the filament is 1.0 A and 2.0 A.

(8 marks)

(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.

(2 marks)

(Total 12 marks) Q2.

A filament lamp rated 12 V, 1.0 A has a resistance of 4.0 when it carries no current.

(a) On the axes below, sketch the form of the current against voltage characteristic for this lamp. (4)

(b) The filament lamp is one example of a non-ohmic device.

(i) State what is meant by the term non-ohmic.

(1)

(ii) Name one other example of a non-ohmic device.

(1)
(Total 6 marks) Q3.

(a) Draw, on the axes below, the current/voltage characteristic for a filament lamp. Do not insert any values for current or voltage. (3 marks)

(b) Explain why the characteristic has the shape you have drawn.

(3 marks)

(c) The current/voltage characteristic of a filament lamp is to be determined using a datalogger, the data then being fed into a computer to give a visual display of the characteristic. Draw the circuit diagram required for such an experiment and state what is varied so as to produce a range of values.

(5 marks)
(Total 11 marks) Q4. The characteristic shown below is that of a filament lamp. (a) Explain why, as the voltage is increased either positively or negatively from zero, the characteristic has the form shown in the diagram

(5 marks)

(b) At a certain point on the characteristic, the power developed in the lamp is 20 W and the current is 90 mA. Calculate the resistance of the filament at this point on the characteristic.

(2 marks)

(Total 7 marks) Q5. When a filament lamp is switched on it takes 0.50 seconds for the filament to reach its normal operating temperature. The way in which the current changes during the first second after switching on is shown on the graph below. (a) Use the graph to determine the maximum current through the lamp.

(1 mark)

(b) Assuming that the lamp is connected to a 12V dc supply of a negligible internal resistance,

(i) Calculate the resistance of the lamp when it has reached its normal operating temperature,

(1 mark)

(ii) Calculate the power of the lamp when it has reached its normal operating temperature.

(1 mark)

(c) Explain why the current through the lamp decreases between 0.05 s and 0.50 s.

(2 marks)

(d) State and explain the change, if any, to the final current through the lamp if it is connected to the same supply with another similar lamp

(i) in series,

(2 marks)

(ii) in parallel.

(2 marks)

(e) State and explain why a filament lamp is most likely to fail as it is switched on.

(2 marks)

(Total 11 marks) Q6.

(a) Sketch, on the axes below, the current–voltage (IV) characteristic for a filament lamp for currents up to its working power. [2 marks]

(b)

(i) State what happens to the resistance of the filament lamp as the current increases.

[1 mark]

(ii) State and explain whether a filament lamp is an ohmic or non-ohmic conductor up to its working power.

[1 mark]

(c) Three identical filament lamps, P, Q and R are connected in the circuit as shown below: The filament in lamp Q melts so that it no longer conducts. Explain why lamp P becomes brighter and lamp R becomes dimmer.

[2 marks]

(d) A filament lamp, X, is rated at 60 W 230 V.

Another type of lamp, Y, described as 'energy saving' has the same light intensity output but is rated at 11 W 230 V.

(i) Calculate the electrical energy converted by each lamp if both are on for 4 hours a day for a period of 30 days.

[2 marks]

(ii) Suggest why the two lamps can have different power ratings but have the same light intensity output.

[2 marks]

(Total 10 marks) 