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When a telescope is adjusted for paralle...

When a telescope is adjusted for parallel light, the distance of the objective from the eyepiece is 100 cm for normal adjustment. The magnifying power of the telescope in this case is 9. If an old man cannot see beyond 90 cm and wishes to use the telescope, then he will have to reduce the tube length by

A

1.5 cm

B

0.5 cm

C

1 cm

D

2 cm

Text Solution

Verified by Experts

The correct Answer is:
C
`(L_(0))/(L_(e))=9 " and "L_(0)+L_(e)=100`
`L_(0)=90`
`L_(e)=10`
Now
`underset("cm")overset("Now")(1/-90)"-(1)/(u)=(1)/(10)implies u=(-90)/(10)=-9`
Tube length = 9 + 90 = 99 cm
change = 1 cm
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