What is a lens? What are its types? Define the basic terminologies of lenses.

A lens is a transparent optical device that bends light.

Types:

1. Convex lens (Converging lens): Thicker in the center, brings light together.

2. Concave lens (Diverging lens): Thinner in the center, spreads light apart.

Terminologies:

Optical center (O): The center of the lens.

Principal axis: A straight line passing through the center of the lens.

Principal focus (F): The point where parallel rays meet (convex) or appear to diverge (concave).

Focal length (f): Distance between optical center and focus.

Related Questions:

  1. What is reflection of light? Define the following terms: Incident ray, reflected ray, normal, angle of incidence, and angle of reflection. Describe the laws of reflection.
  2. What are different spherical mirrors? Define different terms involved in spherical mirrors.
  3. Why is a concave mirror called a converging mirror? Why is a convex mirror called a diverging mirror?
  4. Define the principal focus of convex and concave mirrors. Define focal length. Which mirror has a positive focal length? Which has a negative focal length and why?
  5. What is the spherical mirror formula? Also, write down the sign conventions for the spherical mirror formula.
  6. Differentiate between real and virtual images. What are three basic rays by which we can draw a ray diagram to form an image by a spherical mirror?
  7. What is refraction of light? Show by ray diagram how light bends when it travels from rare to denser medium and from denser to rare medium. Define the refractive index of a medium. What are its different formulae?
  8. What are the laws of refraction? Explain with the help of ray diagrams
  9. Explain the phenomenon of total internal reflection. What are necessary conditions to perform total internal reflection? Derive the formula for the refractive index of a medium in terms of the critical angle.
  10. What is optical fibre? How does light travel through it? Explain.
  11. When you look at the front side of a polished spoon, your image is inverted, and from the back of the spoon, your image is erect. Explain why?
  12. Which mirror is used by girls for makeup and why?
  13. Why are large convex mirrors fixed at blind turns of mountains?
  14. Which mirrors are used for the rear view of vehicles and why?
  15. If a person is walking in a pool, why do his legs appear shorter in water?
  16. Why do diamonds sparkle brightly?
  17. When white light passes through a prism, it disperses into its seven colors. Why does dispersion take place in a prism?
  18. A magnifying glass can burn the paper. How is it possible?
  19. Your grandfather uses spectacles to read a newspaper. You see through the spectacles and observe that objects behind it were inverted. Why was it so observed?
  20. Under what condition does a convex lens nearly act as a diverging lens?