The boy walks towards the mirror at a speed of 1m/ s. At what speed does his image approach him?
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When the boy walks towards the mirror at a speed of 1m/ s, his image will also appear to move towards the mirror at the same speed of 1m/ s. So, the speed at which his image approach him will be 2m/ s + 2m/ s = 4m/ s.
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To find the image distance for varying object distances in case of a convex lens of focal length 15 cm, a student obtains on a screen a sharp image of a bright object by placing it at 20 cm distance from the lens. After that he gradually moves the object away from the lens and each time focuses the image on the screen.
In which direction-towards or away from the lens does he move the screen to focus the object?
How does the size of image change?
Approximately at what distance does he obtain the image of magnification -1?
How does the intensity of image change as the object moves farther and farther away from the lens?
The absolute refractive indices of glass and water are $4 / 3$ and $3 / 2$ respectively. If the speed of light in glass is $2 \times 10^8$ $m / s$, calculate the speed of light in (i) vacuum, (ii) water.
The refractive indices of three media are given below :
Medium
Refractive Index
A
1.6
B
1.8
C
1.5
A ray of light is travelling from $A$ to $B$ and another ray is travelling from $B$ to $C$. (a) In which of the two cases the refracted ray bends towards the normal? (b) In which case does the speed of light increase in the second medium? Give reasons for your answer.
You are provided with two lenses of focal lengths 10cm and 20cm. Which of the two lenses would you suggest to obtain greater convergence on refracted light? Justify your choice.