How Lenses Work

• What is the main topic of today's video?

  Focus and dispersion of light using lenses
• How do lenses focus light?

  By using refraction to bend light rays
• 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
• What is another name for a convex lens?

  Converging lens
• How do concave lenses affect parallel rays of light?

  They refract them outwards, dispersing light
• How do we determine the direction of refracted rays in lenses?

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

  The point where light rays converge or appear to diverge
• 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?

  By increasing its curvature or changing material
• What is the difference between real and virtual images?

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

  When light rays actually converge to form the image
• What happens to light rays from an object like a spanner?

  They form a real image on the retina
• Why don't we notice the inversion of real images?

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

  When light rays do not actually converge
• What is the most 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 that block light
• What should you mention when describing images in exams?

  Whether they are real or virtual, upright or inverted
• How would you describe the real image in the example on the left?

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

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

  • Convex lenses converge light rays
  • Concave lenses disperse light rays
  • All lenses have a principal focus on both sides
  • Focal length determines lens power
• What are the differences between real and virtual images?

  Real Images:

  • Formed by actual convergence of light rays
  • Can be captured on a screen
  • Typically inverted

  
  

  Virtual Images:

  • Formed by apparent convergence of light rays
  • Cannot be captured on a screen
  • Typically upright