Assertion and Reason for Ch 9 Light, Reflection and Refraction Class 10 Science
Important QuestionsA
Answer
(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.
1
Reason (R): Concave mirror converges the light rays falling on it to a point.
Answer
(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
Concave mirror converges the light rays falling on it to a point. So large concave mirrors are used to concentrate sunlight to produce heat in solar cookers.
2
Reason (R): Plane mirror forms virtual image, if objects is real.
Answer
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
Plane mirror forms virtual image of real object and real image of virtual object.
3
Reason (R): The convex lens can give diverging rays.
Answer
(d) Assertion (A) is false but reason (R) is true
If the rays cross focal point of convex lens, they become diverging.
4
Reason (R): A ray of light along the normal has angle of incidence as π/2 and hence, it retraces its own path after reflection from mirror.
Answer
(c) Assertion (A) is true but reason (R) is false.
Angle of incidence = Angle between incident ray normal to the mirror = 0°
5
Reason (R): The focal length of a concave mirror is independent of the medium in which it is placed.
Answer
(d) Assertion (A) is false but reason (R) is true.
Focal length is the property of mirror and is independent of the medium in which it is placed.
6
Reason (R): Only real objects are photographed.
Answer
(c) Assertion (A) is true but reason (R) is false.
An image is a plane mirror is virtual and it can be photographed.
7
Reason (R): The image formed by a concave mirror is certainly virtual if the object is real.
Answer
(c) Assertion (A) is true but reason (R) is false
The image of real object may be real in case of concave mirror.
8
Reason (R): The focal length of a convex mirror of radius R is equal to, f = R/2
Answer
(d) Assertion (A) is false but reason (R) is true.
Focal length of the spherical mirror does not depend on the medium which it placed.
9
Reason (R): Refractive index of the material of the core of the optical fibre is greater than of air.
Answer
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
Optical fibre communication is based on the phenomenon of total internal reflection at core – clade interface. The refractive index of the material of the cladding, hence, light sinking at core – cladding interface gets totally internal reflected. The light undergoes and reaches the other end of the fibre.
10
Reason (R): Refractive index of a pair of media depends on the wavelength of light used.
Answer
(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
Refractive index of any pair of media is inversely proportional to wavelength of light.
Hence,
γu < γr
μr < μv
where, γu and γr are the wavelengths of violet and red light. μr and μv are refractive index of violet and red light.