Physics
Assertion (A) : A student is given a spherical mirror of focal length -10 cm. He identifies it as a concave mirror.
Reason (R) : Focal length of a concave mirror is always positive.
- both A and R are true and R is the correct explanation of A
- both A and R are true and R is not the correct explanation of A
- assertion is false but reason is true
- assertion is true but reason is false
Answer
assertion is true but reason is false
Explanation
Assertion (A) is true because according to sign conventions (the mirror formula uses the Cartesian system), the focal length of a concave mirror is negative. So, a mirror with focal length –10 cm is indeed a concave mirror.
Reason (R) is false because the focal length of a concave mirror is always negative in mirror formula sign convention.
Related Questions
Assertion (A) : For an object placed symmetrically when the angle θ between the mirrors is 72°, the number of images formed is 4.
Reason (R) : If n = 360°/θ is odd, the number of images for an object placed symmetrically is equal to n.
- both A and R are true and R is the correct explanation of A
- both A and R are true and R is not the correct explanation of A
- assertion is false but reason is true
- assertion is true but reason is false
Assertion (A) : Concave mirror is used as doctor's head mirror.
Reason (R) : If a parallel beam of light is incident on a concave mirror, the mirror focuses the beam to a point.
- both A and R are true and R is the correct explanation of A
- both A and R are true and R is not the correct explanation of A
- assertion is false but reason is true
- assertion is true but reason is false
What is a spherical mirror?
Define centre of curvature of a spherical mirror.