Edexcel GCSE Physics: Light and the Electromagnetic Spectrum

The electromagnetic (EM) spectrum is a continuous range of waves, divided into seven regions.

Describe and explain the main features of the electromagnetic spectrum. In your answer you should: name the seven regions in order; state a property that all EM waves share; describe how the frequency, wavelength and energy change across the spectrum; and give one named use and one danger of a region of your choice. (6 marks)

A radio station broadcasts using electromagnetic waves. The waves travel through the air at a speed of 3.0 × 10⁸ m/s and have a frequency of 1.0 × 10⁸ Hz.

(a) Calculate the wavelength of the radio waves. Use $v = f\lambda$v=fλ. Show your working and give the unit. (3 marks)

(b) State one property that these radio waves share with all other electromagnetic waves. (1 mark)

A ray of light passes from air into a glass block. The angle of incidence in air is 40° and the refractive index of the glass is 1.5.

(a) Calculate the angle of refraction inside the glass. Use $n = \dfrac{\sin i}{\sin r}$n=sinrsini​, rearranged as $\sin r = \dfrac{\sin i}{n}$sinr=nsini​. Show your working. (2 marks)

(b) State whether the ray bends towards or away from the normal as it enters the glass. (1 mark)

(You may use $\sin 40° = 0.643$sin40°=0.643.)

Optical fibres carry light signals using total internal reflection (TIR).

(a) State the two conditions that must be met for total internal reflection to occur. (2 marks)

(b) Name the type of EM radiation produced by changes in the nucleus of a radioactive atom. (1 mark)

When light reflects off a smooth mirror it produces a clear image (specular reflection), but when it reflects off a sheet of paper it does not (diffuse reflection).

Explain why a smooth mirror produces a clear image while a sheet of paper does not, even though both obey the law of reflection. (2 marks)

Across the electromagnetic spectrum, the regions are arranged in order of frequency.

Name the EM region that has the highest frequency and carries the most energy. (1 mark)