Lenses and magnification: Waves: Physics: GCSE (9:1)

• Lens


  A shaped piece of transparent glass or plastic that forms an image by refracting light

  
• Convex (converging) lens


  A lens that is thicker in the middle than it is at the edges and causes light rays to converge

  
• Concave (diverging) lens


  A lens that is thinner in the middle than it is at the edges. and causes light rays to diverge

  
• Converge


  When light rays move together to meet at a common point
• Diverge


  When a light ray splits up or spreads out
• Principal focus (focal point)


  The focus of a lens where light rays appear to converge or to diverge from

  
• How a convex lens works

  Parallel rays of light move together and are brought to a focus at the principal focus

  
• How a concave lens works

  Parallel light rays spread out and separate but appear to come from a principle focus on the other side of the lens

  
• Focal length


  The distance from the lens to the principal focus

  
• Real image


  An image that can be projected onto a screen

  
• Virtual image


  An image that appears to come from behind the lens

  
• Type of image formed by convex lens


  Real or virtual

  
• Type of image formed by concave lens


  Always virtual
• Magnification


  A measure of the size of an image compared to the size of the object

  
• Equation for magnification

  magnification = image height / object height

  
• Units for magnification

  Magnification is a ratio so has no units but both heights should be measured using the same unit