OxfordAQA International GCSE Physics: The electromagnetic spectrum: uses, hazards, infrared and X-rays (9203) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover section 3.3.2, The electromagnetic spectrum (statements a to m), of the OxfordAQA International GCSE Physics (9203) specification, for exams May/June 2018 onwards. The qualification is untiered. Question 7 draws on content marked for the full Physics award. Use c = 3.00 × 10⁸ m/s for the speed of EM waves in a vacuum.

Read the study guide or the revision notes first. Course pages: the OxfordAQA IGCSE Physics hub and the printable checklist.

Questions

1. (a) State whether electromagnetic waves are transverse or longitudinal. [1] (b) State what electromagnetic waves transfer, and where it is transferred from and to. [2]

2. The following are all parts of the electromagnetic spectrum: gamma rays, microwaves, ultraviolet, radio waves, visible light, X-rays, infrared. Write them in order of increasing wavelength. [3]

3. A TV remote control sends infrared of wavelength 940 nm. Calculate the frequency of the infrared. [3]

4. (a) Calculate the frequency of a gamma ray of wavelength 1.0 × 10⁻¹² m. [2] (b) A radio wave has wavelength 3.0 m. Calculate how many times greater the frequency of the gamma ray is than the frequency of the radio wave. [2]

5. A space probe is 7.5 × 10⁹ m from Earth. A command is sent by radio waves. (a) Calculate the time taken for the command to reach the probe. [2] (b) The probe replies at once. Calculate the time between sending the command and receiving the reply. [1]

6. A student has two identical metal cans, one painted matt black and one shiny silver. Each holds the same mass of water at 20 °C. The cans stand the same distance from a radiant heater. After 10 minutes the water in the black can is at 44 °C and the water in the silver can is at 30 °C. In a second test, both cans are filled with water at 78 °C and left to cool. After 10 minutes the black can is at 49 °C and the silver can is at 63 °C. (a) Calculate the temperature rise of each can in the first test and how many times larger the black can’s rise is. [2] (b) State what the first test shows about the two surfaces. [1] (c) Calculate the temperature fall of each can in the second test and state what the second test shows. [2] (d) State one variable the student must keep the same. [1]

7. (a) State what is meant by black-body radiation. [1] (b) The element of an electric heater is switched on. At first it feels warm but looks the same. After a while it glows dull red and later bright orange. Explain these observations. [4]

8. Choose the electromagnetic wave that fits each job. [5] (a) night vision devices (b) security marking (c) satellite television (d) killing harmful bacteria in food (e) medical imaging of bones

9. (a) State the hazard of overexposure to microwaves and the hazard of overexposure to infrared. [2] (b) State two hazards of overexposure to ultraviolet. [2] (c) A hiker spends a day on a snow-covered mountain. Suggest two ways the hiker can reduce the risk from ultraviolet. [2]

10. (a) Explain what is meant by ionisation. [1] (b) Explain why gamma rays are more hazardous to the human body than microwaves. [2] (c) State the harm to a cell that gamma rays can cause. [1]

11. A dental X-ray uses X-rays of wavelength 0.015 nm. The X-rays are detected on photographic film placed inside the mouth. (a) Calculate the frequency of these X-rays. [3] (b) The developed image shows a pale outline for a tooth with a metal filling and the jawbone, but a darker region for the gum. Explain why. [3] (c) Suggest three precautions that reduce the exposure of the dental staff and the patient. [3]

12. (a) Describe how X-rays can be used to treat some cancers, and explain why the dose is carefully controlled. [3] (b) State what a CT scan does and give one medical condition that X-rays can help to diagnose. [2] (c) A hospital monitors the radiation exposure of its radiographers. State how this can be done and explain why it is needed. [3]

Answers

1. (a) Transverse. [1] (b) Energy [1], transferred from a source to an absorber [1]. [3] Examiner insight: On a question like this, answers that name energy score; answers that say the waves carry “matter”, “heat” only, or “power” with no source and absorber are weaker.

2. Gamma rays are shortest and radio waves longest, so those two go at the ends [1]. Then X-rays, ultraviolet, visible light in that order [1], and infrared then microwaves before the radio waves [1]. Order: gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves, radio waves. [3] Examiner insight: Check the direction asked for. A correct list written from longest to shortest is the wrong way round for “increasing wavelength” and is unlikely to earn full credit.

3. λ = 940 nm = 9.40 × 10⁻⁷ m [1]. f = c / λ = (3.00 × 10⁸) / (9.40 × 10⁻⁷) [1]. f = 3.19 × 10¹⁴, so 3.2 × 10¹⁴ Hz [1]. [3] Examiner insight: Show the conversion from nanometres. A final answer that is out by a power of ten usually signals a missed conversion, and clear working helps the marker see where the slip happened.

4. (a) f = c / λ = (3.00 × 10⁸) / (1.0 × 10⁻¹²) [1] = 3.0 × 10²⁰ Hz [1]. (b) Radio frequency = (3.00 × 10⁸) / 3.0 = 1.0 × 10⁸ Hz [1]. Ratio = (3.0 × 10²⁰) / (1.0 × 10⁸) = 3.0 × 10¹² times [1]. [4] Examiner insight: A ratio has no unit. Give the number of times, and use standard form so the size is clear.

5. (a) Time = distance / speed = (7.5 × 10⁹) / (3.00 × 10⁸) [1] = 25 s [1]. (b) The signal makes the journey twice: 2 × 25 = 50 s [1]. [3] Examiner insight: Part (b) rewards noticing the journey is made twice. Writing the equation time = distance / speed before substituting makes your method easy to follow.

6. (a) Black: 44 − 20 = 24 °C and silver: 30 − 20 = 10 °C [1]. Ratio = 24 / 10 = 2.4 times [1]. (b) The matt black surface absorbs more infrared than the shiny silver surface, so it is the better absorber [1]. (c) Black fell 78 − 49 = 29 °C and silver fell 78 − 63 = 15 °C [1]. The black can lost energy faster, so a dark, matt surface is a better emitter of infrared [1]. (d) Any one from: mass of water, starting temperature, size or material of the can, distance from the heater [1]. [6] Examiner insight: Link each result to a property (absorber, emitter). “The black can is better” is incomplete; “the black can is a better absorber, because its rise was larger” is a stronger answer.

7. (a) The range of electromagnetic radiation emitted by an object at a particular temperature [1]. (b) Every object emits infrared, and the warm element gives out infrared that you feel but cannot see [1]. As it gets hotter it radiates more infrared in a given time [1]. It also radiates at higher frequencies [1], which reach into the visible range, first red and then orange as higher frequencies are added [1]. [5] Examiner insight: Strong answers make both points about heating: more radiation, and higher frequencies. A reply that says only “it gets hotter so it glows” does not explain the colour change.

8. (a) Infrared [1]. (b) Ultraviolet [1]. (c) Microwaves [1]. (d) Gamma rays [1]. (e) X-rays [1]. [5] Examiner insight: Give one wave for each use. Listing two waves for the same use risks losing the mark if one of them is wrong.

9. (a) Microwaves: heating of body tissue [1]; infrared: skin burns [1]. (b) Skin cancer [1] and blindness [1]. (c) Wear sunscreen or cover exposed skin [1]; wear sunglasses or goggles that block ultraviolet [1]. [6] Examiner insight: A protection measure should match the hazard. “Wear clothes” is vague; “cover the skin to block ultraviolet” shows why it works.

10. (a) Ionisation is the removal of an electron from an atom or molecule [1]. (b) Gamma rays have much higher energy than microwaves [1], enough to cause ionisation, whereas microwaves only have a heating effect [1]. (c) Genetic mutations (damage to the cell’s genetic material) [1]. [4] Examiner insight: Say that gamma rays can cause ionisation. “Gamma rays are radioactive” does not answer a question about the energy of the wave.

11. (a) λ = 0.015 nm = 1.5 × 10⁻¹¹ m [1]. f = (3.00 × 10⁸) / (1.5 × 10⁻¹¹) [1]. f = 2.0 × 10¹⁹ Hz [1]. (b) Metal and bone absorb X-rays strongly [1], whereas gum, as healthy soft tissue, transmits them [1]. Less radiation reaches the film behind the tooth and bone, so those areas stay paler [1]. (c) Any three from, one mark each: the dental staff stand behind a screen or leave the room during the exposure; the patient wears a lead apron; short exposure times; staff wear a monitoring badge; only take an X-ray when it is needed [3]. [9] Examiner insight: In explanations about images, name both the tissue and what happens to the X-rays. Stating only “bone is dense” misses the property the question is looking for: absorption.

12. (a) A beam of X-rays is aimed at the tumour [1] and the high dose kills the cancer cells [1]. The dose is controlled because X-rays also damage healthy cells [1]. (b) CT scanning uses X-rays to build up detailed images of the inside of the body [1]. Any one of: bone fractures, dental problems [1]. (c) Staff wear a monitoring badge (for example a film badge) [1] that records their exposure [1], so the exposure can be checked and kept low, because ionising radiation can be dangerous [1]. [8] Examiner insight: For “explain why” parts, finish with the reason, not just the method. Writing “to keep exposure low because ionising radiation is harmful” completes the answer.

Where marks are usually lost

• Writing the spectrum in the wrong direction, or putting microwaves and infrared the wrong way round.
• Leaving wavelengths in nanometres or frequencies in megahertz when substituting into the wave equation.
• Giving a final answer with no unit, or with a unit from a different quantity.
• Saying “the black can is better” without saying that it is a better absorber or emitter of infrared.
• Forgetting that all objects emit infrared, and that hotter objects emit more.
• Answering a black-body question with temperature alone, without mentioning higher frequencies.
• Naming a hazard without naming the wave that causes it, or giving a protection measure that does not match the hazard.
• Saying that X-rays “go through bone” rather than being absorbed by it.

Next steps

• Re-read the revision notes and the study guide.
• Course pages: OxfordAQA IGCSE Physics hub and the printable checklist.
• Take the free 10-minute diagnostics to find your weakest topics.
• Book a free trial class for help with anything you got wrong.

Official syllabus

OxfordAQA International GCSE Physics (9203), for exams May/June 2018 onwards, published by OxfordAQA, section 3.3.2 The electromagnetic spectrum.