The electromagnetic spectrumIB MYP Physics: Subtopic test

1. 1
   A smartphone uses several parts of the electromagnetic spectrum. It uses radio waves for mobile calls, microwaves for Wi-Fi, infrared for face recognition and visible light from its screen.

   (a)

   Which list shows the electromagnetic waves in order of increasing frequency?

   [1 mark]

   • AGamma, X-ray, ultraviolet, visible, infrared, microwave, radio
   • BRadio, infrared, microwave, visible, ultraviolet, X-ray, gamma
   • CRadio, microwave, infrared, visible, ultraviolet, X-ray, gamma
   • DRadio, microwave, visible, infrared, ultraviolet, gamma, X-ray

   (b)

   Which statement is true for all electromagnetic waves travelling in a vacuum?

   [1 mark]

   • AThey all travel at the same speed of 3 × 10⁸ m/s
   • BThey all have the same frequency
   • CThey are all longitudinal waves
   • DThey all need a medium to travel through

   (c)

   Radio waves have a longer wavelength than visible light. State how the frequency of radio waves compares with that of visible light and explain why.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A local radio station broadcasts at a frequency of 100 MHz (1.0 × 10⁸ Hz). A home Wi-Fi router uses microwaves with a frequency of 2.4 GHz (2.4 × 10⁹ Hz). All electromagnetic waves travel at 3.0 × 10⁸ m/s in air.

   (a)

   What is the wavelength of the radio waves from the station?

   [1 mark]

   • A0.33 m
   • B30 m
   • C6 m
   • D3 m

   (b)

   A second station broadcasts at 200 MHz. What is the wavelength of its radio waves?

   [1 mark]

   • A0.67 m
   • B1.5 m
   • C6 m
   • D3 m

   (c)

   Calculate the wavelength of the microwaves used by the Wi-Fi router.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student tests how well different sunscreens block ultraviolet (UV) radiation. She uses special beads that change from white to purple when UV hits them, and scores the colour from 0 (white) to 5 (darkest purple). Each sample of beads is covered with clear plastic film. She spreads a thin layer of sunscreen on the film, then shines the same UV lamp on the sample for 10 minutes. The film with no sunscreen gives a score of 5. The film with SPF 15 sunscreen gives 3, SPF 30 gives 2 and SPF 50 gives 1.

   (a)

   State a hypothesis for this investigation, with a scientific reason, and identify one control variable.

   [3 marks]

   (b)

   Describe the trend in the results and explain what the result for the film with no sunscreen shows. Explain why the results are important for health.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A hospital in Nairobi uses X-rays to image broken bones. It also buys single-use plastic syringes that a factory sterilises inside their sealed packs by exposing them to gamma rays. Heat cannot be used for this because it would melt the plastic. The staff at the factory work behind very thick concrete walls.

   (a)

   Explain why X-rays can be used to image broken bones, and why they are dangerous.

   [6 marks]

   (b)

   Discuss and evaluate the use of gamma rays to sterilise the syringes.

   [6 marks]

   Total for question 4: 12 marks

End of questions