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TS EAMCET · Physics · Ray Optics

A convex lens focusses an object 20 cm from it on a screen placed 5 cm away from it. A glass plate (refractive index =75) of thickness 1.4 cm is inserted between the lens and the screen. What is the distance of the object from the lens, so that its image is again focused on the screen?

  1. A 22.5 cm
  2. B 30.7 cm
  3. C 25.0 cm
  4. D 28.4 cm
Verified Solution

Answer & Solution

Correct Answer

(B) 30.7 cm

Step-by-step Solution

Detailed explanation

Apparent shift in position due to a glass slab is given by d=t1-1μ. ⇒d=1.41-57=0.4 cm For refraction without glass slab, u=-20 cm, v=5 cm. Applying lens equation, 1f=1v-1u=15+120⇒f=4 cm For refraction with glass slab inserted,…
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