Concepts Of Physics MCQ Edition [Volume 1]PhysicsGeometrical Optics
A converging lens with a focal length of 15 cm and a converging mirror with a focal length of 10 cm are positioned 50 cm apart, sharing a common principal axis. A point source is situated between the lens and the mirror, at a distance of 40 cm from the lens. Determine the locations of the two images formed.
Options
- A24 cm from the lens towards the mirror, and 15 cm from the lens away from the mirror
- B15 cm from the lens towards the mirror, and 24 cm from the lens away from the mirror
- C15 cm and 24 cm from the lens, both on the side away from the mirror
- D10 cm and 30 cm from the lens, both on the side away from the mirror
Correct answer
C. 15 cm and 24 cm from the lens, both on the side away from the mirror
Step-by-step solution
The light from the point source can form an image in two ways: by directly refracting through the lens, and by first reflecting from the mirror and then refracting through the lens. For the first image (formed directly by the lens): The source is at a distance of 40 cm from the lens. Using the lens formula 1 v₁ - 1 u = 1 f : 1 v₁ - 1 -40 = 1 15 1 v₁ = 1 15 - 1 40 = 8 - 3 120 = 1 24 v₁ = +24 cm The positive sign indicates that the image is formed on the side opposite to the object, which is away from the mirror. For