Edexcel GCSE Physics
Edexcel GCSE Physics Topic 5: Light and the Electromagnetic Spectrum Exam Questions
Free Edexcel GCSE Physics exam questions for Topic 5: Light and the Electromagnetic Spectrum, with a mark scheme for every pack. Covers reflection, refraction, total internal reflection, lenses, colour, the electromagnetic spectrum, its uses, dangers and black body radiation.
Topic 5: Light and the Electromagnetic Spectrum exam questions
2 question packs of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About Edexcel GCSE Physics Topic 5: Light and the Electromagnetic Spectrum
Topic 5 on Paper 1 builds on Topic 4 by focusing on light and the rest of the electromagnetic spectrum. Separate physics students study ray diagrams for reflection and refraction, total internal reflection and critical angle, specular and diffuse reflection, colour and filters, and converging and diverging lenses. Everyone learns the order, properties, uses and dangers of electromagnetic waves, and how all objects emit and absorb radiation depending on their temperature. Examiners often ask you to complete ray diagrams, explain the dangers of ultraviolet, X-rays and gamma rays, and describe the core practicals on refraction in a glass block and on infrared emission from different surfaces.
What you need to know
- Reflection and refraction The angle of incidence equals the angle of reflection. Light refracts towards the normal when it enters a denser medium such as glass because it slows down.
- Total internal reflection Happens when light travels from a denser to a less dense medium and the angle of incidence is greater than the critical angle. Used in optical fibres.
- Colour Objects appear coloured because they reflect some wavelengths and absorb others. Filters transmit only certain colours and absorb the rest.
- Lenses Converging lenses bring parallel rays to a principal focus and can form real or virtual images; diverging lenses spread rays out and form virtual images. A more curved lens has a shorter focal length and is more powerful.
- EM spectrum In order of increasing frequency: radio, microwaves, infrared, visible, ultraviolet, X-rays, gamma rays. All are transverse and travel at 3 x 10^8 m/s in a vacuum.
- Uses and dangers Uses include radio for broadcasting, microwaves for cooking and satellites, infrared for heating and cameras, UV for security marking, X-rays for imaging and gamma for sterilising. UV can cause skin cancer; X-rays and gamma are ionising and can damage cells and DNA.
- Radiation and temperature All bodies emit and absorb radiation. Hotter objects emit more radiation at shorter wavelengths. An object at constant temperature emits radiation at the same rate as it absorbs it.
Common mistakes in Topic 5: Light and the Electromagnetic Spectrum
- Drawing refracted rays bending the wrong way. Light bends towards the normal when it slows down entering glass and away from the normal when it speeds up leaving it.
- Saying microwaves or radio waves are ionising. Only high frequency UV, X-rays and gamma rays are ionising.
- Saying a red filter turns light red. It absorbs all other colours and only transmits red.
- Measuring angles from the surface instead of the normal. All angles of incidence, reflection and refraction are measured from the normal.
- Forgetting that higher frequency means shorter wavelength. All EM waves have the same speed in a vacuum, so v = f x lambda links them inversely.
Try three Topic 5: Light and the Electromagnetic Spectrum exam-style questions
1. A radio wave has a frequency of 1.5 x 10^8 Hz. The speed of electromagnetic waves is 3.0 x 10^8 m/s. Calculate its wavelength. (3 marks)
Show the mark scheme answer
lambda = v / f; = 3.0 x 10^8 / 1.5 x 10^8; = 2.0 m.
2. State two conditions needed for total internal reflection. (2 marks)
Show the mark scheme answer
Light must travel from a denser medium into a less dense medium (e.g. glass to air); the angle of incidence must be greater than the critical angle.
3. Explain why gamma rays are more dangerous to the body than radio waves. (3 marks)
Show the mark scheme answer
Gamma rays have a much higher frequency so carry more energy; they are ionising; they can damage cells or DNA and cause mutations or cancer, whereas radio waves are not ionising.
Topic 5: Light and the Electromagnetic Spectrum FAQs
What does Edexcel GCSE Physics Topic 5 Light and the Electromagnetic Spectrum cover?
It covers reflection, refraction, total internal reflection, lenses, colour, the EM spectrum with its uses and dangers, and how temperature affects the radiation an object emits.
Which paper is Topic 5 examined on?
Topic 5 is assessed on Paper 1.
How should I remember the order of the electromagnetic spectrum?
Use a mnemonic for radio, microwaves, infrared, visible, ultraviolet, X-rays, gamma, and remember that frequency and energy increase while wavelength decreases along that order.
