The electromagnetic spectrumIB MYP Sciences: Subtopic test

1. 1
   A science teacher in Mumbai draws the electromagnetic spectrum on the board and asks her class to compare radio waves, visible light and gamma rays. She reminds them that all electromagnetic waves are transverse and that sunlight reaches Earth across empty space.

   (a)

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

   [1 mark]

   • AThey travel at the same speed, 3 × 10⁸ m/s
   • BThey have the same frequency
   • CThey have the same wavelength
   • DThey are longitudinal waves

   (b)

   Which list shows electromagnetic waves in order of increasing frequency?

   [1 mark]

   • AGamma rays, X-rays, ultraviolet, visible light
   • BRadio waves, infrared, visible light, ultraviolet
   • CMicrowaves, radio waves, infrared, visible light
   • DUltraviolet, visible light, infrared, microwaves

   (c)

   A radio station broadcasts at a frequency of 100 MHz. The speed of radio waves is 3 × 10⁸ m/s. Calculate the wavelength of the radio waves.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In a hospital in Lagos, a patient with a broken wrist has an X-ray. The radiographer stands behind a lead screen to operate the machine. Later the hospital uses gamma rays to sterilise surgical instruments before they are sealed in packets.

   (a)

   Why can an X-ray image show the bones of the wrist?

   [1 mark]

   • ABones give out X-rays that the detector records
   • BSoft tissue absorbs more X-rays than bone
   • CBone absorbs more X-rays than soft tissue, so fewer reach the detector behind it
   • DX-rays are reflected by the bones

   (b)

   Why does the radiographer stand behind a lead screen?

   [1 mark]

   • ATo stop the X-ray beam from heating her skin
   • BTo keep the patient still
   • CTo see the image more clearly
   • DX-rays are ionising and repeated exposure can damage cells and cause cancer

   (c)

   Explain how gamma rays can be used to sterilise surgical instruments.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Students in Perth, Australia, investigate sun protection. They place identical UV-sensitive beads under clear plastic film coated with sun cream of SPF 15, SPF 30 or SPF 50, and under film with no cream. The beads change from white to purple in ultraviolet light. The students time how long the beads take to become fully purple in strong sunlight, and each test is done once. The times are 25 s with no cream, 95 s with SPF 15, 170 s with SPF 30 and 290 s with SPF 50.

   (a)

   State a testable hypothesis for this investigation, with a scientific reason, and identify the independent variable.

   [3 marks]

   (b)

   Describe the trend in the results and suggest two ways to improve the investigation.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   In many countries, young people use sunbeds to get a tan. Sunbeds give out ultraviolet radiation. Ultraviolet radiation can damage skin cells and cause skin cancer, but it also helps the skin to make vitamin D, which is needed for strong bones. Some countries have banned sunbeds for people under 18, while the tanning industry argues that it provides jobs and that people should be free to choose.

   (a)

   Explain the hazards of ultraviolet radiation, X-rays and gamma rays.

   [6 marks]

   (b)

   Discuss the benefits and drawbacks of banning sunbeds for under-18s, and evaluate whether the ban is justified.

   [6 marks]

   Total for question 4: 12 marks

End of questions