Lenses and Images

Lenses and Images

1. Different lenses produce different kinds of image

   • Converging Lens
     • Convex - bulges outwards
       • Causes parallel rays of light to converge (move together) at a focus
       • Principal focus is where rays hitting the lens parallel to the axis meet
   • Diverging Lens
     • Concave - caves inwards
       • Causes parallel rays of light to diverge (spread out)
     • Principal focus is the point where rays hitting the lens parallel to the axis appear to all come from
   • The distance from the centre of the lens to the principal focus is called the focal length

2. 3 Rules for refraction in a converging lens

   • An incident ray parallel to the axis refracts through the lens and passes through the principal focus on the other side
   • An incident ray passing through the principal focus refracts through the lens and travels parallel to the axis
   • An incident ray passing through the centre of the lens carries on in the same direction

3. 3 Rules for refraction in a diverging lens

   • An incident ray parallel to the axis refracts through the lens, and travels in line with the principal focus (so it appears to have come from the principal focus)
   • An incident ray passing through the lens towards the principal focus refracts through the lens and travels parallel to the axis
   • An incident ray passing through the centre of the lens carries on in the same direction

4. Lenses can produce real and virtual images

   • A real image is where the light from an object comes together to form an image on a 'screen' - like the image formed on the eye's retina
   • A virtual image is when the rays are diverging, so the light from the object appears to be coming from a completely different place

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