Verified Solution • 2025–26 Session moderate

QJEEM19Pha825: JEE Main 2019 Physics - Class 12 JEEM19Pha825 Solution: An object is at a distance of 20 m from a convex lens of focal…

An object is at a distance of 20 m from a convex lens of focal length 0.3 m. The lens forms an image of the object. If the object moves away from the lens at a speed of 5 m/s, the speed and direction of the image will be :

Multiple Choice Options

  • A 1.16 ×\times 10–3 m/s towards the lens
  • B 2.26 ×\times 10–3 m/s away from the lens
  • C 3.22 × 10–3 m/s towards the lens
  • D 0.92 ×\times 10 −- 3 m/s away from the lens

Step-by-Step Verified Solution

From lens equation

1v−1u=1f{1 \over v} - {1 \over u} = {1 \over f}

1v−1(−20)=1(.3)=103{1 \over v} - {1 \over {\left( { - 20} \right)}} = {1 \over {\left( {.3} \right)}} = {{10} \over 3}

1v=103−120{1 \over v} = {{10} \over 3} - {1 \over {20}}

1v=19760;v=60197{1 \over v} = {{197} \over {60}};v = {{60} \over {197}}

m = (vu)\left( {{v \over u}} \right) = (60197)20{{\left( {{{60} \over {197}}} \right)} \over {20}}

velocity of image wrt. to lens is given by

vI/L = m2vO/L

direction of velocity of image is same as that of object

vO/L = 5 m/s

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