Eduqas GCSE Physics 6 Light and Electromagnetic Waves Exam Questions

About Eduqas GCSE Physics 6 Light and Electromagnetic Waves

Light and electromagnetic waves in Eduqas GCSE Physics has five parts: the frequency range of the spectrum, interactions of electromagnetic radiation with matter and their applications, lenses, colour, and black body radiation (qualitative only). You learn the order and properties of the electromagnetic spectrum, the uses and hazards of each region, reflection and refraction with ray diagrams, convex and concave lenses, how colour depends on absorption, transmission and reflection, and how emission depends on temperature. Examiners often ask for ray diagrams and explanations of refraction. SP6.2 and SP6.3 cover refraction in a glass block and images in lenses.

What you need to know

• 6.1 The spectrum In order of increasing frequency: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays. All are transverse and travel at the same speed in a vacuum, 3 x 10^8 m/s. Wavelength decreases as frequency increases.
• 6.2 Uses and hazards Radio waves for communication, microwaves for cooking and satellites, infrared for heaters and cameras, visible light for fibre optics, UV for sun beds and security marks, X-rays and gamma rays for medical imaging and treatment. UV can damage skin; X-rays and gamma rays are ionising and can cause mutations and cancer.
• 6.2 Reflection and refraction The angle of incidence equals the angle of reflection, measured from the normal. Light refracts when it changes speed at a boundary: it bends towards the normal when entering a denser medium. SP6.2: investigate refraction in a glass block using a ray box and protractor.
• 6.3 Lenses A convex lens converges light to a principal focus and can form real or virtual images; a concave lens diverges light and forms virtual images. Draw ray diagrams with a ray parallel to the axis passing through the focus and a ray through the centre undeviated. SP6.3: investigate images in convex and concave lenses.
• 6.4 Colour Objects appear coloured because they reflect certain wavelengths and absorb others. A red object reflects red light. Filters transmit only their colour. White objects reflect all wavelengths; black objects absorb all of them.
• 6.5 Black body radiation All bodies emit radiation; hotter bodies emit more radiation and at shorter wavelengths. An object at constant temperature absorbs and emits radiation at the same rate. The Earth's temperature depends on the balance between radiation absorbed and emitted.

Common mistakes in 6 Light and Electromagnetic Waves

• Saying EM waves travel at different speeds in a vacuum. All EM waves travel at 3 x 10^8 m/s in a vacuum.
• Measuring angles from the surface of the glass block. Angles of incidence and refraction are measured from the normal.
• Saying light bends because it enters a different material. Explain that it changes speed at the boundary, which makes it change direction.
• Saying a red filter turns light red. It absorbs other colours and only transmits red light.
• Saying all EM radiation is dangerous. Only higher frequency radiation (UV, X-rays, gamma) is ionising or damaging to cells; radio waves are not ionising.

Try three 6 Light and Electromagnetic Waves exam-style questions