Reflection and refraction

• Reflection of waves can occur when waves hit a surface and are reflected back.
• Refraction of waves occurs when waves pass through a medium and are refracted.
• Reflection of waves is required for practical work.
• Reflection of waves is a key concept in physics.
• Reflection and refraction of light explain how people see images, colour and even optical illusions.
• Refraction is the change in direction of a wave at a boundary between two transparent materials.
• Different materials have different densities.
• Reflection of waves is a fundamental concept in physics.
• Light waves may change direction at the boundary between two transparent materials.
• Refraction is the process by which a wave changes speed and sometimes direction upon entering a denser or less dense medium, for example, a light ray changes direction when refracted by a lens.
• A ray diagram represents the direction and angle of travel of light to show the refraction of a wave at a boundary.
• Refraction can cause optical illusions as the light waves appear to come from a different position to their actual source.
• The density of a material affects the speed that a wave will be transmitted through it.
• In general, the denser the transparent material, the more slowly light travels through it.
• Glass is denser than air, so a light ray passing from air into glass slows down.
• The reflection and refraction of light explains how people see images, colour and even optical illusions.
• All waves will reflect and refract in the right circumstances.
• The reflection of light by different types of surface and the refraction of light by different substances are key elements in understanding how people see images, colour and even optical illusions.
• To investigate the reflection of light by different types of surface and the refraction of light by different substances, set up a ray box, slit and lens so that a narrow ray of light is produced.
• If a ray meets the boundary at an angle to the normal, it bends towards the normal.
• A light ray speeds up as it passes from glass into air, and bends away from the normal by the same angle.
• When a ray hits a glass block at right angles to the surface, the wave slows, its wavelength decreases as it enters glass, and as the wave returns to air, speed and wavelength increase to original values.
• Although the wave slows down, its frequency remains the same, due to the fact that its wavelength is shorter.
• In this diagram, the right hand side of the incoming wave slows down before the left hand side does, causing the wave to change direction.
• The diagram shows that as a wave travels into a denser medium, such as water, it slows down and the wavelength decreases.
• Place a 30 centimetre (cm) ruler near the middle of a piece of plain A3 paper.
• A useful way of remembering the speed and direction changes of light during refraction is 'FAST': Faster - Away / Slower - Towards.
• For a given frequency of light, the wavelength is proportional to the wave speed, so if a wave slows down, its wavelength will decrease.
• Draw a straight line parallel to its longer sides on the piece of plain A3 paper.
• Use a protractor to draw a second line at right angles to the first line on the piece of plain A3 paper.
• Label the second line with an ‘N’ for ‘normal’ on the piece of plain A3 paper.
• Place the longest side of a rectangular acrylic polymer close to the piece of plain A3 paper.
• With the normal near the middle of the block, carefully draw around the block without moving it on the piece of plain A3 paper.
• Use the ray box to shine a ray of light at the point where the normal meets the block on the piece of plain A3 paper.
• The angle between the normal and the incident ray is called the angle of incidence on the piece of plain A3 paper.
• Join the crosses to show the paths of the light rays.
• The results for a polymer block: Angle of incidence (°) Angle of reflection (°) Angle of refraction (°) ..
• Compare the angle of incidence with the angle of reflection for each block.
• Measure the angle of incidence, angle of refraction and angle of reflection for each block.
• Move the ray box or paper to change the angle of incidence.