KVPY2015PhysicsRay Optics
A point source of light is moving at a rate of 2 ~cm - s ⁻¹ towards a thin convex lens of focal length 10 ~cm along its optical axis. When the source is 15 ~cm away from the lens the image is moving at
Options
- A4 ~cm - s ⁻¹ towards the lens
- B4 ~cm - s ⁻¹ away from the lens
- C8 ~cm - s ⁻¹ towards the lens
- D8 ~cm - s ⁻¹ away from the lens
Correct answer
D. 8 ~cm - s ⁻¹ away from the lens
Step-by-step solution
array l d v d t = -v² u² d u d t & 1 v = 1 F + 1 u 1 ~V = 1 10 + 1 -15 1 v = 3-2 30 v =30 ~cm array dv dt = ( 30 15 )² 2 =8 ~cm / s away from lens