Theory: answer each printed part. For drawings, upload a clear photo of your sketch on the supplied figure; show working and units for calculations.
A filament lamp is arranged above a shiny metal surface, as shown in Fig. 8.1. A student reads in a textbook that a light-emitting diode (LED) is more efficient than a filament lamp.
(a)(i)State what is meant by ‘efficiency’.
Answer guidance
State A short answer. No explanation is needed, and adding one cannot earn extra marks.
[1 mark]
(a)(ii)Suggest why the efficiency of a filament lamp is very low.
Answer guidance
Suggest More than one answer may be acceptable, so long as it is consistent with the physics.
[1 mark]
(b)
The student considers replacing the filament lamp shown in Fig. 8.1 with an LED of the same brightness. Data about the filament lamp and a suitable LED are shown in Table 8.1.
Table 8.1
input power / W
energy efficiency
filament lamp
120
6.2%
LED
15
—
Swipe sideways to see all columns.
The LED emits the same amount of visible light as the filament lamp. Using this information and the data in Table 8.1, determine the efficiency of the LED.
Answer guidance
Using You must use the thing it names. An answer that reaches the right value another way may not score.
[2 marks]
(c)(i)The filament lamp is connected to the live and neutral wires in the mains supply. The earth wire in the mains supply is connected to the shiny metal surface shown in Fig. 8.1. There is a fuse in the live wire. By accident, the live wire touches the shiny metal surface. Describe what then happens.
Answer guidance
Describe Say what happens, in order. Reasons are not required unless the question also asks why.
[2 marks]
(c)(ii)The filament lamp is connected to the live and neutral wires in the mains supply. The earth wire in the mains supply is connected to the shiny metal surface shown in Fig. 8.1. There is a fuse in the live wire. By accident, the live wire touches the shiny metal surface. In another similar lamp, the fuse is wrongly connected into the earth wire. Explain why a person is not protected when the live wire touches the shiny metal surface.
Answer guidance
Explain Give reasons, not just what happens. Each distinct reason is usually worth a mark.
[2 marks]
5054/21/M/J/23Cambridge O Level Physics 5054 · May/June 2023 · Paper 2 variant 1 · Question 8