How Lenses Work

• How do lenses focus and disperse light?

  Using refraction
• What are the two main types of lenses?

  Convex and concave lenses
• What shape do convex lenses have?

  Outwards bulge in the center
• What happens to parallel rays of light when they pass through a convex lens?

  They refract inwards to a single point
• How do concave lenses affect parallel rays of light?

  They disperse the light outwards
• What is another name for a convex lens?

  Converging lens
• How do we determine the direction of refracted rays in a lens?

  By tracing virtual lines from the principal focus
• What is the principal focus of a lens?

  The point where light rays converge
• What is the distance between the principal focus and the center of the lens called?

  Focal length
• How does the focal length relate to the power of a lens?

  Shorter focal length means more powerful lens
• How can you make a lens more powerful?

  Make it more curved or use stronger material
• What is the difference between real and virtual images?

  Real images are formed by actual light rays
• How is a real image formed?

  When light rays converge to form the image
• Where do light rays from an object like a spanner form a real image?

  On the retina of the eye
• Why don't we notice the inversion of real images?

  Our brain corrects the inverted image
• How are virtual images formed?

  When light rays do not actually converge
• What is a common example of a virtual image?

  Images seen in a mirror
• Why can't real rays be behind a mirror?

  Because mirrors are solid objects
• What should you mention when describing images in exams?

  Whether they are real or virtual, upright or inverted
• How would you describe the image of the chicken's head in the example?

  Real, inverted, and smaller than the object
• How would you describe the image on the right in the example?

  Virtual, upright, and smaller than the object
• What are the characteristics of lenses?

  • Convex lenses bulge outwards
  • Concave lenses cave inwards
  • Both types have a principal focus
  • Principal focus is on both sides
  • Focal length affects lens power
• What are the steps to determine the type of image formed by a lens?

  1. Identify if the image is real or virtual
  2. Determine if the image is upright or inverted
  3. Assess if the image is larger or smaller than the object