(a) With the help of a labelled diagram, explain how a concave lens perges a beam of parallel light rays. Mark the principal axis, optical centre, principal focus and focal length of the concave lens on the diagram.(b) State whether concave lens has a real focus or a virtual focus.(c) List some things that concave lens and concave mirror have in common.
(a) When a parallel beam of light rays falls on a concave lens, the rays get diverged or spread out after passing through the lens. As the refracted rays are diverging away from one another, they do not actually meet at a point. These diverging rays, when produced backward, appear to meet at a point $F$ (focus), on the left side of the lens.
(b) A concave lens has a virtual focus since the light rays do not actually pass through the focus.
(c) Some things that concave lens and concave mirror have in common are as follows:
1. Both diverge a parallel beam of light.
2. Both always form a virtual image.
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- (a) With the help of a labelled diagram explain how a convex lens converges a beam of parallel light rays. Mark the principal axis, optical centre, principal focus and focal length of the convex lens on the diagram.(b) State whether convex lens has a real focus or a virtual focus.(c) List some things that convex lens and concave mirror have in common.
- (a) Explain with the help of a diagram, why the concave lens is also called a perging lens.(b) Define the principal focus of a concave lens.
- (a) Define (i) principal focus of a concave mirror, and (ii) focal length of a concave mirror.(b) Draw diagram to represent the action of a concave mirror on a beam of parallel light rays. Mark on this diagram principal axis, focus F, centre of curvature C, pole P and focal length f, of the concave mirror.
- Explain with a suitable diagram, how a concave mirror converges a parallel beam of light rays. Mark clearly the pole, focus and centre of curvature of concave mirror in this diagram.
- A convex lens is said to have a real focus and a concave lens a Virtual Focus.Why?
- Define the principal focus of a concave mirror.
- You are provided with a concave mirror, a convex mirror, a concave lens and a convex lens. To obtain an enlarged image of an object you can use either$(a)$. concave mirror or convex mirror.$(b)$. concave mirror or convex lens.$(c)$. concave mirror or concave lens.$(d)$. concave lens or convex lens.
- (a) Explain with the help of a diagram, why the convex lens is also called a converging lens.(b) Define principal axis, principal focus and focal length of a convex lens.
- You are provided with a convex mirror, a concave mirror, a convex lens and a concave lens. You can get an inverted image from$(a)$. both concave lens and convex lens.$(b)$. both concave mirror and convex mirror.$(c)$. both concave mirror and convex lens.$(d)$. both convex mirror and concave lens.
- Which of the following can make a parallel beam of light when light from a bulb falls on it?(a) concave mirror as well as concave lens (b) convex mirror as well as convex lens(c) concave mirror as well as convex lens (d) convex mirror as well as concave lens
- When sunlight is concentrated on a piece of paper by a spherical mirror or lens, then a hole can be burnt in it. For doing this, the paper must be placed at he focus of:(a) either a convex mirror or convex lens (b) either a concave mirror or concave lens(c) either a concave mirror or convex lens (d) either a convex mirror or concave lens
- What happens after refraction, when :(i) a ray of light parallel to the principal axis passes through a concave lens?(ii) a ray of light falls on a convex lens while passing through its principal focus?(iii) a ray of light passes through the optical centre of a convex lens?
- Draw ray diagram to show the principal focus of a:(i) concave mirror(ii) convex mirror
- What is a lens? Distinguish between a convex lens and concave lens. Which of the two is a converging lens : convex lens of concave lens?
- A spherical mirror and a spherical lens each have a focal length of, –15 cm. The mirror and the lens are likely to be:(a) both concave.(b) both convex.(c) the mirror is concave but the lens is convex.(d) the mirror is convex but the lens is concave.
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