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A light ray enters from medium A to medium B as shown in Figure 10 The refractive index of medium B relative to A will be
- greater than unity
- less than unity
- equal to unity
greater than unity
We see that
Ray of light bends towards the normal as we go from medium A to medium B
And we know that
When ray goes from rarer to denser medium, it bends towards normal
So, that means Refractive index of B is greater than A
Thus, Refractive index of B relative than A = Refractive index of B/Refractive Index of A
Since, Refractive index of B > Refractive index of A
Refractive index of B relative than A > 1
Which of the following statements is true?
- A convex lens has 4 dioptre power having a focal length 0.25 m
- A convex lens has –4 dioptre power having a focal length 0.25 m
- A concave lens has 4 dioptre power having a focal length 0.25 m
- A concave lens has –4 dioptre power having a focal length 0.25 m
(a) A convex lens has 4 dioptre power having a focal length 0.25 m
In all the cases,
Focus length is positive
So, it will be a convex lens
Power of a lens = 1/ focal length
For focal length = 0.25m
Power of the lens = 1/0.25
= 4 D
Thus, it is a convex lens with power 4 D
So, (a) is the correct answer
The laws of reflection hold good for
- plane mirror only
- concave mirror only
- convex mirror only
- all mirrors irrespective of their shape
all mirrors irrespective of their shape
Explanation - The laws of reflection are obeyed by all mirrors irrespective of their shape surface.
The path of a ray of light coming from air passing through a rectangular glass slab traced by four students are shown as A, B, C and D in Figure. Which one of them is correct?
The correct image looks like
The refractive index of glass is more than the refractive index of air.
Hence, glass is more optically dense than air.
Case I - Ray of light enters from air to glass
When a ray of light enters from air to glass, it bends towards the normal.
Case II - Ray of light enters from glass to air
When a ray of light enters from glass to air, it bends away from the normal.
The above two cases are only depicted correctly in (B),
Hence (B) is the correct answer
A child is standing in front of a magic mirror. She finds the image of her head bigger, the middle portion of her body of the same size and that of the legs smaller. The following is the order of combinations for the magic mirror from the top.
- Plane, convex and concave
- Convex, concave and plane
- Concave, plane and convex
- Convex, plane and concave
Concave, plane and convex
Explanation - The image of the head is larger. An enlarged image is formed by a concave mirror, hence the mirror on the top is a concave mirror .
The middle portion of the body is of the same size.
An image of the same size is formed by a plane mirror, hence the middle part of the mirror is a plane mirror .
The image of the legs is smaller.
A diminished image is formed by a convex mirror, hence the mirror on the bottom is a convex mirror .
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