# OCR - P1: Radiation and waves

 P1.4 What happens when light and sound meet different materials? Background to the topic What you should be able to do: A beam of light is reflected from a smooth surface, such as a mirror, in a single beam which makes the same angle with the normal as the incident beam (specular reflection). Light is scattered in all directions from an uneven surface. Light is refracted at the boundary between glass (and water and Perspex) and air; this property is exploited in prisms and lenses. When a beam of white light is passed through a prism, the emerging light beam is spread out showing the colours of the spectrum. This can be explained using the wave model, different colours have different wavelengths; different wavelengths travel at different speeds when passing through glass, water or Perspex. What we perceive as white light is a mixture of different colours, ranging in wavelength from violet light (shortest visible wavelength) to red light (longest visible wavelength). A coloured filter works by allowing light of one or more wavelength through (transmission) and absorbing light of the other wavelengths. An object appears white if it scatters all the colours of light that fall on it, and black if it scatters none (and absorbs all). It appears coloured if it scatters light of some colours and absorbs light of other colours. Its observed colour is that of the light it scatters. 1. Construct and interpret two-dimensional ray diagrams to illustrate specular reflection by mirrors 2. Construct and interpret two-dimensional ray diagrams to illustrate refraction at a plane surface and dispersion by a prism 3. Use ray diagrams to illustrate the similarities and differences between convex and concave lenses 4. Describe the effects of transmission, and absorption of waves at material interfaces 5. Explain how colour is related to differential absorption, transmission, and scattering 6. Describe, with examples, processes in which sound waves are transmitted though solids 7. Explain that transmission of sound through the bones in the ear works over a limited frequency range, and the relevance of this to human hearing Sound travels better through solids and liquids than through air. The small bones in the middle ear transmit the sound waves from the air outside to the inner ear. The bones transmit frequencies most efficiently in the range 1 kHz and 3 kHz. The ways in which sound waves are transmitted, reflected and refracted as they pass through liquids and solids are exploited: in ultrasound imaging in medicine, in exploring the structure of the Earth and in using SONAR to explore under water. 8. Explain, in qualitative terms, how the differences in velocity, absorption and reflection between different types of waves in solids and liquids can be used both for detection and for exploration of structures which are hidden from direct observation, notably: a) in our bodies (ultrasound imaging) b) in the Earth (earthquake waves) c) in deep water (SONAR) 9. Show how changes, in speed, frequency and wavelength, in transmission of sound waves from one medium to another, are inter-related.