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a concave mirror forms a real image 3 times larger than the object on the screen object and screen are mover until image becomes twice as that of object. if shift is 6 cm shift of screen and focal length is 36,36 36,16 72,36 none

a concave mirror forms a real image 3 times larger than the object on the screen object and screen are mover until image becomes twice as that of object. if shift is 6 cm shift of screen and focal length is
  1. 36,36
  2. 36,16
  3. 72,36
  4. none

Grade:11

1 Answers

Rishwanth
70 Points
3 years ago
The answer is 36 and 36
1/f=1/v-1/u
1/f=1/3u+1/u  (consider the sign convention)
f=3u/4
Second case
1/f=1/2(u+6)+1/(u+6)
f=2(u+6)/3
Equating the both equations we get
u=48
First case v=3×48=144
Second case v=2×(48+6)=108 hence shift of screen is 144-108=36 and focal length =36
I hope it clears.
 

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