Electromagnetic spectrum

Which row orders three electromagnetic waves from lowest frequency to highest frequency?

1. A

   radio → visible → X-ray

2. B

   X-ray → visible → radio

3. C

   visible → radio → X-ray

4. D

   radio → X-ray → visible

1. a

   Select and explain Select the correct row, then state what happens to wavelength as frequency increases in a vacuum.

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   Correct choiceA

   1. 1

      Selects option A: radio, visible, then X-ray is the order of increasing frequency.

   2. 2

      States that wavelength decreases as frequency increases.

   3. 3

      Links the inverse relationship to the same wave speed in a vacuum, using c = fλ or equivalent reasoning.

A school compares three electromagnetic communication links. Use a wave speed of 3.00 × 10⁸ m s⁻¹ in air.

1. a

   Calculate Calculate the wavelength of the 2.40 GHz Wi-Fi signal.

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   1. 1

      Converts 2.40 GHz to 2.40 × 10⁹ Hz.

   2. 2

      Uses λ = c ÷ f.

   3. 3

      Obtains λ = 0.125 m.

2. b

   Compare Identify which link has the shortest wavelength and justify your answer.

   2
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   1. 1

      Identifies the fibre laser.

   2. 2

      Explains that it has the greatest frequency and therefore the shortest wavelength at the same wave speed.

3. c

   State State one limitation of treating all three links as travelling at exactly the vacuum speed.

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   1. 1

      States that waves travel more slowly in materials such as glass fibre, or that air speed is only approximately the vacuum value.

A clinic is deciding whether an X-ray image is justified for a patient with a painful wrist after a fall. The examination suggests a fracture, but the patient has already had several medical images this year.

1. a

   Explain Explain why X-rays can reveal a bone fracture more clearly than surrounding soft tissue.

   2
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   1. 1

      States that bone absorbs or attenuates more X-rays than most surrounding soft tissue.

   2. 2

      Links the different transmitted intensities to contrast in the detector image.

2. b

   Distinguish Distinguish the hazard of X-rays from the risk in this particular decision.

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   1. 1

      Identifies ionising radiation and possible biological damage as the hazard.

   2. 2

      Explains that risk depends on dose, frequency of exposure, shielding, body region, and the probability or consequence of harm.

3. c

   Evaluate Evaluate whether the image should be taken, using both benefit and exposure evidence.

   3
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   1. 1

      Uses the diagnostic benefit, such as confirming location or severity and guiding treatment.

   2. 2

      Uses an exposure consideration, including previous imaging while recognising that each justified image should use the lowest suitable dose.

   3. 3

      Gives a balanced conditional conclusion and recognises that a qualified clinician makes the final decision with the patient.