Light & the Electromagnetic SpectrumEdexcel GCSE Physics: Topic test

20 questions, 54 marks

Edexcel GCSE Physics

Light & the Electromagnetic Spectrum topic test

Total 54 marks

Name

Class

Date

1
An engineer is testing a glass optical fibre designed to carry telephone signals as pulses of infrared light. The core of the fibre has a higher refractive index than the thin cladding layer that surrounds it. As light travels along the core, it repeatedly strikes the boundary between the core and the cladding at an angle of incidence greater than the critical angle for that boundary.
(a)
What name is given to the process that keeps the light travelling inside the core each time it strikes the core-cladding boundary?
[1 mark]
ATotal internal reflection
BDiffuse reflection
CPartial refraction
DDiffraction
(b)
The cladding is manufactured with a lower refractive index than the core. Why is this difference in refractive index necessary for the fibre to work?
[1 mark]
AIt ensures the light slows down enough in the cladding to travel faster once it re-enters the core
BIt ensures the critical angle at the boundary is small enough that rays travelling along the core strike it above the critical angle
CIt stops the infrared light from being absorbed by the glass as heat
DIt increases the frequency of the light so that more signals can be sent per second
(c)
A section of the cladding is accidentally scratched away, so that the fibre core is exposed directly to air at that point. Explain what is likely to happen to a ray of light that reaches this exposed section at the same angle of incidence it previously used at the core-cladding boundary, and why.
[2 marks]
Total for question 1: 4 marks
2
A hospital radiology department uses several different parts of the electromagnetic spectrum for different jobs. One machine fires a beam of a highly penetrating, high-frequency radiation through a patient's chest onto a detector plate to produce an image of the ribs and lungs. A second, separate device uses a lower-frequency, longer-wavelength radiation to warm a patient's muscles gently before physiotherapy, without producing any image at all.
(a)
Which type of electromagnetic radiation is most likely being used to produce the image of the patient's ribs and lungs?
[1 mark]
ARadio waves
BInfrared radiation
CX-rays
DVisible light
(b)
Which type of electromagnetic radiation is most likely being used to warm the patient's muscles before physiotherapy?
[1 mark]
AGamma radiation
BUltraviolet radiation
CX-rays
DInfrared radiation
(c)
State two safety precautions that hospital staff should take to protect themselves when they regularly operate the imaging machine described above, and briefly explain why each precaution is needed.
[2 marks]
Total for question 2: 4 marks
3
A photography student places a red filter in front of a camera lens and points the camera at a poster containing patches of pure red, pure green and pure blue paint under white light. She then photographs the same poster using a converging (convex) lens on the camera with the red filter removed.
(a)
Explain, in terms of absorption and transmission of light, why the red patch on the poster appears bright through the red filter, while the green and blue patches appear almost completely black.
[3 marks]
(b)
The student then removes the filter and photographs the poster using the camera's converging lens. Explain how a converging lens forms a focused image of the poster on the camera's sensor, referring to what happens to rays of light from a single point on the poster as they pass through the lens.
[4 marks]
Total for question 3: 7 marks
4
A weather research station monitors a small greenhouse used to grow plants. The greenhouse has glass walls that let visible light from the Sun pass through easily, but the soil and plants inside absorb this visible light and re-emit the absorbed energy as infrared radiation, some of which is then trapped inside the greenhouse rather than escaping straight back out through the glass. On a sunny afternoon, researchers record that the greenhouse's internal temperature is rising steadily.
(a)
Explain, in terms of the power absorbed and the power radiated by the greenhouse, why its internal temperature rises steadily on the sunny afternoon described above, and explain what must happen to the rate at which the greenhouse radiates energy as its temperature keeps rising.
[6 marks]
(b)
The researchers replace the greenhouse's clear glass panels with dark-tinted glass panels of a similar thickness. Explaining your reasoning using ideas about absorption, transmission and emission of radiation, predict and explain how the internal steady-state temperature of the greenhouse with dark-tinted glass is likely to compare with the original clear-glass greenhouse under the same sunlight.
[6 marks]
Total for question 4: 12 marks
5
A submarine periscope uses two flat, highly polished metal mirrors mounted parallel to each other inside a long vertical tube, each tilted at 45 degrees to the vertical. Light from a distant ship enters the top of the tube, reflects off the upper mirror, travels down the tube, and reflects off the lower mirror before reaching the operator's eye. The mirrors are kept highly polished rather than being left with a dull, matt metal surface.
(a)
What type of reflection takes place at each of the two polished mirrors inside the periscope?
[1 mark]
ASpecular reflection
BDiffuse reflection
CTotal internal reflection
DPartial refraction
(b)
If the mirrors were left with a dull, matt surface instead of being polished, what effect would this most likely have on the periscope?
[1 mark]
ALight would undergo total internal reflection at each mirror instead, forming a brighter image
BLight would be scattered in many directions at each mirror, so no clear image would reach the operator's eye
CThe wavelength of the reflected light would decrease, making the image appear blue-shifted
DThe image would still form perfectly, because reflection does not depend on surface smoothness
(c)
Using the law of reflection, describe how the direction of a ray of light changes when it reflects off one of the periscope's 45-degree mirrors, in terms of the angle of incidence and the angle of reflection.
[2 marks]
Total for question 5: 4 marks
6
A telecommunications company operates a mobile phone mast that transmits signals using microwaves, and a separate radio transmitter nearby that broadcasts a local radio station using radio waves of a much longer wavelength. Residents living close to the mast are concerned about possible health effects of long-term exposure to the microwave signal, and an engineer explains that the mast's output power is kept within strict, legally regulated limits.
(a)
Compared with the radio waves broadcast by the local radio transmitter, how do the microwaves transmitted by the mobile phone mast differ in frequency and wavelength?
[1 mark]
AMicrowaves have a lower frequency and a longer wavelength than the radio waves
BMicrowaves and radio waves always have exactly the same frequency and wavelength
CMicrowaves have a higher frequency and a shorter wavelength than the radio waves
DMicrowaves travel at a different speed through a vacuum than radio waves do
(b)
The engineer explains that the potential danger of electromagnetic radiation to human tissue generally depends on its frequency. Based on this, why are the mast's microwaves considered less hazardous to residents than higher-frequency radiations such as ultraviolet or x-rays would be at the same power?
[1 mark]
AMicrowaves do not transfer any energy to the objects that absorb them
BMicrowaves cannot travel through air, so they never reach nearby residents
CMicrowaves are not part of the electromagnetic spectrum, unlike ultraviolet and x-rays
DThe potential danger of electromagnetic radiation increases with increasing frequency, and microwaves have a much lower frequency than ultraviolet or x-rays
(c)
State one possible harmful effect on the human body of excessive exposure to microwave radiation, and one possible harmful effect of excessive exposure to the much higher-frequency ultraviolet radiation.
[2 marks]
Total for question 6: 4 marks
7
A student sets up two identical small metal containers of water, each fitted with a thermometer. Container P has its outer surface painted matt black, and container Q has its outer surface left as bare, polished metal. Both containers start at the same temperature and are placed the same distance from an electric heater, which radiates infrared energy towards them equally, for the same length of time.
(a)
Predict and explain which container, P or Q, will show the greater rise in water temperature during the experiment, referring to the surfaces' ability to absorb thermal radiation.
[3 marks]
(b)
The heater is then switched off, and both containers are left to cool in a room at constant temperature. Explain which container is likely to cool down faster, and why this is consistent with the fact that good absorbers of thermal radiation are also good emitters.
[4 marks]
Total for question 7: 7 marks
8
A science demonstrator shines a narrow beam of white light from a ray box through a triangular glass prism onto a white screen. As the light passes through the prism, it emerges as a fan-shaped band of colours spreading from red at one edge through to violet at the other. The demonstrator explains that this happens because white light is actually a mixture of electromagnetic waves of different wavelengths within the visible part of the spectrum, and that glass refracts each wavelength by a slightly different amount.
(a)
Explain, in terms of refraction and wavelength, why the white light entering the prism separates out into a spread of different colours as it emerges from the prism, and explain why red light and violet light end up refracted by different amounts.
[6 marks]
(b)
The demonstrator then replaces the white light source with an infrared source and a microwave source in turn, aiming each beam at the same glass prism, but no visible fan of colours is seen from either. Explain why the eye cannot detect any dispersed beams in these two cases, and describe one everyday use each of infrared radiation and microwave radiation that does not rely on it being visible to the eye.
[6 marks]
Total for question 8: 12 marks

End of questions