AQA GCSE Physics 4.6.2 Electromagnetic Waves Exam Questions

About AQA GCSE Physics 4.6.2 Electromagnetic Waves

This AQA GCSE Physics section covers the electromagnetic spectrum from radio waves to gamma rays. You need the order of the spectrum, the properties shared by all EM waves, a required practical on infrared emission from different surfaces, the hazards of ultraviolet, X-rays and gamma rays, and practical uses of each region. Higher tier only content includes explaining refraction with wavefronts and how radio waves are produced and absorbed. Physics only content covers lenses, ray diagrams and magnification, and the colours of visible light and filters. It is examined on Paper 2.

What you need to know

• The spectrum EM waves are transverse and transfer energy from source to absorber. They form a continuous spectrum and all travel at the same speed through a vacuum (space). In order of increasing frequency: radio, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays. Our eyes only detect visible light.
• Properties and refraction Different substances may absorb, transmit, refract or reflect EM waves in ways that vary with wavelength. Refraction is a change of direction when a wave changes speed at a boundary. Higher tier only: explain refraction using wave front diagrams, as part of the wave front slows first.
• Infrared required practical Investigate how the amount of infrared radiation absorbed or radiated by a surface depends on its nature, for example using a Leslie cube with an infrared detector or thermometer. Matt black surfaces are the best emitters and absorbers; shiny silver surfaces are the worst.
• Producing EM waves (Higher tier only) Radio waves can be produced by oscillations in electrical circuits, and when absorbed they may create an alternating current with the same frequency. Changes in atoms and nuclei can generate or absorb radiation over a wide frequency range; gamma rays originate from changes in the nucleus.
• Hazards Ultraviolet waves can cause skin to age prematurely and increase the risk of skin cancer. X-rays and gamma rays are ionising radiation that can cause the mutation of genes and cancer. Radiation dose (in sieverts) measures the risk of harm.
• Uses Radio: television and radio. Microwaves: satellite communications and cooking. Infrared: electrical heaters, cooking, infrared cameras. Visible light: fibre optic communications. Ultraviolet: energy efficient lamps, sun tanning. X-rays and gamma: medical imaging and treatments.
• Lenses (physics only) Convex lenses form real or virtual images; concave lenses always form virtual images. Magnification = image height / object height (no units). Draw ray diagrams using the principal focus and focal length.
• Visible light (physics only) Each colour has a narrow band of wavelength and frequency. Reflection from smooth surfaces is specular; from rough surfaces is diffuse. Colour filters absorb certain wavelengths and transmit others; opaque objects appear the colour they reflect.

Common mistakes in 4.6.2 Electromagnetic Waves

• Getting the order of the spectrum wrong or saying different EM waves travel at different speeds in a vacuum. All travel at the same speed in a vacuum.
• Saying all EM waves are ionising. Only ultraviolet (high frequency), X-rays and gamma rays are ionising.
• Saying refraction is caused by the wave changing direction. The wave changes speed at the boundary, which causes the change in direction (unless it hits along the normal).
• Giving units for magnification. It is a ratio of two heights, so it has no units.
• Saying a red filter turns light red. It absorbs other colours and transmits only red.

Try three 4.6.2 Electromagnetic Waves exam-style questions