Topic 5 – Light and the Electromagnetic Spectrum

• What do arrows in ray diagrams represent?

  Direction of light travelling

  
• What is the normal in ray diagrams?

  The normal is an imaginary dashed line that is perpendicular to the surface.

  
• What is the incident angle?

  The angle of the entering ray.

  
• What is the reflected angle?

  The angle of the exiting ray.

  
• What is the relationship between incident angle and reflection angle?

  Incident angle equals reflection angle.

  
• How are angles measured in reflection?

  Angles are always measured from the normal.

  
• What happens to light when it enters a denser material?

  It bends towards the normal.

  
• What happens to light when it enters a less dense material?

  It bends away from the normal.
• What is total internal reflection (TIR)?

  TIR occurs when light passes from a denser medium into a less dense medium.

  
• What happens if the angle of incidence is equal to the critical angle?

  The refracted ray will pass along the boundary and not exit the medium.

  
• What is the critical angle?

  The unique angle for each two media at which TIR occurs.
• What happens for angles larger than the critical angle?

  The light internally reflects back into the denser medium.

  
• What are the outcomes when light travels from glass to air based on the angle of incidence?

  • If angle LESS than critical angle, light refracts away from normal.
  • If angle EQUAL to critical angle, light passes along boundary.
  • If angle MORE than critical angle, light reflects.

  
• What is specular reflection?

  Mirror reflection following the law of reflection for a smooth surface.

  
• What is diffuse reflection?

  Light hitting a rough surface is reflected at many angles.

  
• What does each color in visible light represent?

  Each color is a certain wavelength in visible light.

  
• What do all colors together make up?

  White light.
• Why do opaque materials appear to have a certain color?

  They reflect only that certain color light and absorb all other colors.
• What happens when light passes through color filters?

  All other colors are absorbed, and only a certain color is allowed to pass through.
• What is the focal length of a lens?

  The distance between the lens and the focal point.
• What is the focal point of a lens?

  The point where all horizontal rays meet after passing through the lens.

  
• How is the power of a lens defined?

  Power of the lens is the inverse of the focal length.

  
• What is the relationship between focal length and lens power?

  Shorter focal length means greater power.
• How does the thickness of a lens affect its focal length and power?

  Thicker lens means shorter focal length, so greater power.
• What is the shape of concave lenses?

  Concave lenses "cave" inward and are thinner at the center than at the edges.
• What is the function of concave lenses?

  They spread light outwards and make it appear to come from the focal point.

  
• How are concave lenses used in vision correction?

  They are used to correct short-sightedness by spreading out light.

  
• What is the shape of convex lenses?

  Convex lenses are fatter at the center.
• What is the function of convex lenses?

  They focus light inwards and are used for magnifying glasses and binoculars.

  
• How do convex lenses help with long-sightedness?

  They focus rays closer to the eye.

  
• What is a real image?

  A real image is produced at the opposite side of the lens to the object.

  
• What is a virtual image?

  A virtual image appears to come from the same side of the lens as the object.

  
• When does a virtual image occur?


  A virtual image occurs if the object lies closer to the lens than the focal point.

  
• What do all electromagnetic waves do?

  They transfer energy from a source to an observer.

  
• What type of waves are electromagnetic waves?

  They are transverse waves.

  
• How fast do all electromagnetic waves travel in a vacuum?

  They all travel at the same speed.
• Do electromagnetic waves need particles to move?

  No, they do not need particles to move.
• How do materials interact with electromagnetic waves?

  Materials interact differently depending on the wavelength.

  
• What can our eyes detect in terms of electromagnetic waves?

  Our eyes can only detect visible light.

  
• What happens to wavelength and frequency in electromagnetic waves?

  As wavelength decreases, frequency must increase.