Reflection, spherical mirrors, mirror formula
- An object is placed at a distance of 40 cm from a concave mirror of focal length 15 cm. If the object is displaced through a distance of 20 cm towards the mirror, the displacement of the image will be Answer: 3. 36 cm away from the mirror Use the mirror formula 1/v+1/u=1/f with f=-15 cm. Case 1: u=-40 : 1/v=-dfrac115+dfrac140=-5/120⇒ v=-24... 1
- A beam of light from a source L is incident normally on a plane mirror fixed at a certain distance x from the source. The beam is reflected back as a spot on a scale placed just above the source L. When the mirror is rotated through a small angle θ,… Answer: 4. y/2x Key idea: when a mirror rotates by θ , the reflected ray turns by 2θ . The spot moves by y=xtan2θ≈2θ x for small angles. So... 1