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Wednesday, 4 November 2015

Light refraction and reflection questions with answer

1. What is radius of plane mirror?
Ans: Infinity

2. What is angle of reflection for a ray falling normally on a plane mirror?

Ans: 0

3. Why do we use convex surface for side view mirror?

Ans: Convex mirror always form virtual, smaller and upright image of object for vide range.

4. Can a virtual image be photographed?

Ans: yes.

5. What is the power of a plane mirror?

Ans: 0 because focal length is at infinity

6. When the angle of incidence is 90 , what is the angle of refraction?

Ans: 0 degree

7. What is the value of refractive index of air?

Ans: 1. {The ratio of the sines of the angles of incidence and refraction will be the same if the medium is the same.}

8. What is the magnification produced by a plane mirror?

Ans: Plane mirror cannot magnify image and has magnification 1 because height of image formed is equal to that of object.

9. Define power. Give its S.I unit?

Ans: power of a lens is d ability of a lens to converge or diverge an incident rays of light. it is defined as the reciprocal of its focal length d = [1/f(m) ] Dioptre . Its S.I unit is Dioptre.

10. What is power of sun glass?

Ans: sun glasses do not converge or diverge rays of light hence have no power.

11. Between which two points related to a concave mirror should an object be placed to obtain on a screen an image twice the size of the object?

Ans. Between centre of curvature and the principal focus.

12. What are the two factors on which the lateral displacement of an emergent ray from a glass  slab depends ? 

Ans. (i) Angle of incidence (ii) Thickness of glass slab

13.What is the minimum distance between an object and its real image in case of aconcave mirror ? [2011]

Ans. Zero, when object is at centre of curvature, its real image is also formed at the same point.

14. Why do we prefer a convex mirror as a rear-view mirror in vehicles?

Ans. It is because, it covers a wide rear field and forms small, erect and virtual image, close to the eye of the  driver of the vehicle

.Reflection and refraction MCQ 

1.      ray of light strikes the surface of mirror at an angle of 300 with the mirror. The angle of reflection is:
(a)  300
(b) 600
(c) 450
(d) none.

2.      An object 20cm high is placed at a distance of 100 

cm from a plane mirror .The size of the image will be.

(a)  20 cm
(b)  40cm
(c)  10cm
(d)  100cm

3.      Velocity of light in vacuum is
(a)3×108 cm/s
(d)none of these

4.       A concave mirror is a part of a sphere of radius 30cm.It’s focal length is
(a) at infinity
(d) 60cm

5.       Magnification produced by a plane mirror is
(b) zero
(c) +1
(d) infinity

6.       Mirror used for focusing light is
(a) Concave
(b) Convex
(c) plane
(d) none

7.       A concave mirror forms a real and enlarged image of an object if the object is placed at/between
(a) 2F
(b) F
(c) F and C
(d)F and P

8.       Focal length of a plane mirror is
(a)    zero
(c)double of its aperture
(d)half of its aperture

9.       Sin C =
(a) n/1
(b) 1/n
(c) n2

10.   When a ray of light is incident normally, the angle of incidence is
(a) 900
(b) 0
(c) 450
(d) none

11.  A stick in water appears broken due to
(a) reflection of light
(b) refraction of light
(c) total internal reflection
(d) none of these

12.  If angle of incidence is 0then angle of reflection is
(a) 900
(b) 00

13.  Refractive index of diamond with respect to vacuum is 2.5, and then the velocity of light in diamond is.
(a) 25×108 m/s
(c)1.2×108   m/s

14.   Critical angle of a substance is 300.It’s refractive index is
(b) 2

15.   Velocity of light in diamond is

16.   When a ray goes from an optically rarer medium to a denser medium, it
(a)  goes straight
(b)bends away from normal
(c) bends towards normal
(d) reflect back

17.  Lateral displacement is directly proportional to:
(a) Angle of incidence
(b) angle of refraction
(c) Thickness of the slab
(d) velocity of light

18.  n×sinC=
(a) zero
(d) none of these 

19.To a fish, the plane surface of earth appears to be enclosed within an angle of

20.  Power of a lens is 2D, it’s focal length is
(a)-0.5 m
(b)50 cm
(d) 50m

21.  The splitting of light into its component colours is called
(a) refraction
(c) dispertion
(d) diffraction

22.   if ‘i’ is critical angle, ‘r’ is
(a) zero

23.   A drop of water appears like pearl due to
(a)refraction (b) none (c)reflection (d) total internal reflection

24.   curvature of a plane glass is
(c) eqal to C

25.   Mayopia  can be corrected using
(a) concave lens
(b)convex lens 
(c) cylindrical lens
(d) Plano convex lens 

Answer key
1.b                          2.a                          3.c                          4.c                           5.c                         6.a 
7.c                          8.a                          9.b                          10.b                       11.b                       12.b 
13.c                        14.b                       15.b                       16.c                        17.c                        18.b 
19.c                        20.b                       21.c                        22.b                       23.d                       24.a

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