WBCHSE Class 12 Physics Reflection Of Light Multiple Choice Questions

Optics

Reflection Of Light Multiple Choice Questions

Question 1. A ray of light is incident on a reflecting surface making an angle 50° with the surface. Due to reflection, the angle of deviation i

1. 90°
2. 80°
3. 100°
4. 110°

Answer: 100°

Question 2. To form three Images of an object, the angle at which two plane mirrors should be inclined to each other is

1. 30°
2. 60°
3. 90°
4. 120°

Answer: 3. 90°

Question 3. A man moves toward a plane mirror with a velocity 15 m.s^-1 The velocity of the image with respect to the man is

1. 15 m s^-1
2. 30 m-s^-1
3. 35 5 m s^-1
4. 20 m s^-1

Answer: 2. 30 m-s^-1

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Question 4. If two plane mirrors are inclined at an angle of 45° and an object is placed in between them, the number of images formed will 

1. 7
2. 8
3. 14
4. 4

Answer: 1. 7

Question 5. A small object’ is situated at a distance of 10 cm in front of a plane mirror. If you stand behind the object at a distance of 30 cm from the mirror and look at the image, then to the distance of the image will be

1. 60 cm
2. 20 cm40 cm
3. 80 cm

Answer: 3. 40 cm

Question 6. The reflected rays at a plane mirror can form a real image

1. If the incident rays at the mirror are convergent
2. If the incident rays at the mirror are divergent
3. Under no circumstances
4. If the object is situated very close to the mirror

Answer: 1. If the incident rays at the mirror are convergent

Question 7. Light waves coming from the air are reflected at the surface of the separation of air and glass. The phase change of the reflected wave is equal to

1. Zero
2. π/2
3. π
4. 2π

Answer: 1. Zero

Question 8. In the dial of a clock, there are marks instead of numbers. The reading of time appears 10:10 when the clock is seen through a plane mirror. The real-time of the clock is

1. 9:50
2. 1:50
3. 2:10
4. 10:10

Answer: 2. 1:50

Question 9. A man of height 6 ft wants to see his full image in a plane mirror. The minimum length of the plane mirror required is

1. 6ft
2. 12ft
3. 2ft
4. 3f

Answer: 4. 3f

Question 10. The focal length of a concave mirror is

1. Maximum for red color
2. Maximum for violet color
3. Maximum for the yellow color
4. Equal for all colors

Question 11. Which mirror is to be used to obtain a parallel beam of light from a small lamp

1. Plane mirror
2. Convex mirror
3. Concave mirror
4. Any one of these

Answer: 3. Concave mirror

Question 12. A concave mirror has a radius of curvature r and focal length f. An object is placed at a distance from the mirror. The condition under which a diminished inverted image will be formed is

1. u= r
2. u >f
3. f<u>r 0
4. 0 <u <f

Answer:  2. u >f

Question 13. A concave mirror has a radius of curvature of r and a focal length f. An object is placed at a distance from the mirror. The condition under which an inverted image of the same size of the object will be formed is

1. u= r
2. u>= r
3. f<u>r 0
4. 0 <u >f

Answer: 1. u= r

Question 14. A concave mirror has a radius of curvature r and focal length f. An object is placed at a distance from the mirror. The condition under which a virtual image will be formed is

1. u = f
2. u>r
3. f<u>r
4. 0 <u<f

Answer: 4. 0 <u<f

Question 15. A concave mirror has a radius of curvature r and a focal length f. An object is placed at a distance x from the mirror. The condition under which a magnified erect image will be formed is

1. x = f
2. u>r
3. f<u>r
4. 0 <u<f

Answer: 4. 0 <u<f

Question 16. A mirror forms a real image of unit magnification. The nature of the mirror is

1. Plane
2. Paraboloidal
3. Convex
4. Concave

Answer: 4. Concave

Question 17. If an object is placed at a distance of 40 cm from a concave mirror of focal length 20 cm, then the image will be

1. Virtual and inverted
2. Real and erect
3. Real, inverted, and diminished
4. Real, inverted, and the same size as the object

Answer: 4. Real, inverted, and the same size as the object

Question 18. A person standing in front of a mirror finds his image larger than himself. This implies that the mirror is

1. Convex
2. Parabolic
3. Plane
4. Concave

Answer: 4.

Question 19. A convex mirror has a focal length/. An object is placed at a distance from the mirror. The condition under which a diminished image will be formed is

1. u = 0
2. 0<u< ∞
3. u < 0 and |u| <|f|
4. A diminished image will not be formed, in any way

Answer: 2. 0<u< ∞

Question 20. An- object is placed at a distance of 20 cm from a concave mirror of focal length 10 cm. What is the image distance?

1. 20 cm
2. 6.67 cm
3. 10 cm
4. 30 cm

Answer: 1. 20 cm

Question 21. The radius of curvature of a convex mirror is 40 cm and the size of the object is twice the size of the image. The image distance will be

1. 10 cm
2. 20 cm
3. 40 cm
4. 30 cm

Answer: 1. 10cm

Question 22. A concave mirror of focal length / (in air) is immersed in (H s D. The focal length of the concave mirror in water
water will be

1. f
2. 4/3f
3. 3/4 f
4. 7/3f

Answer: 1. f

Question 23. A concave mirror of focal length 15 cm forms an image twice the size of the object. If the image is virtual, the distance of the object is

1. 45 cm
2. 7.5 cm
3. 30 cm
4. 22.5 cm

Answer: 3. 30 cm

Question 24. The image of a point object placed at 10 cm from a concave mirror, is formed at a distance of 20 cm from the mirror. If the object is moved toward the mirror by 0.1 cm then the image

1. Will move another 0.41 cm away from the mirror
2. Will move another 0.81 cm away from the mirror
3. Will move towards the mirror by another 0.41 cm
4. Will move towards the mirror by another 0.81 cm

Answer:  1. Will move another 0.41 cm away from the mirror

Question 25. A small linear object of length b is situated along the axis of a concave mirror at a distance x. If the focal length of the mirror is f, the length of the image will be

1. \(\left(\frac{f}{u-f}\right)\)b
2. \(\left(\frac{f}{u-f}\right)\)² b
3. \(\left(\frac{f}{u-f}\right)\)b²
4. \(\left(\frac{f}{u-f}\right)\)

Answer:  2. \(\left(\frac{f}{u-f}\right)\)² b

Question 26. In the following figure, if the height of an object is  H₁= +2.5 cm, the height of the image H₂ formed is

1. 5cm
2. +5 cm
3. + 7.5 cm
4. – 7.5 cm

Answer:  1. 5cm

Question 27. If the object distance and image distance from the focus of a spherical mirror of focal length ƒ be x and y respec- respectively, then

1. xy= f
2. xy= f²
3. x/y= f
4. xy = f³

Answer: 2. xy= f²

Question 28. An object is placed at a distance x from the principal focus of a spherical mirror of focal length f. The magnification of the image will be

1. x/f
2. f/x
3. 1+f/x
4. 1- f/x

Answer: 2. f/x

Question 29. If a graph is drawn taking x and y as the object distance and the image distance respectively from the focus of a spherical mirror, the graph will be a

1. Rectangular hyperbola
2. Parabola
3. Circle
4.  Ellipse

Answer:   1. Rectangular hyperbola

Question 30. A rod is standing in front of a mirror on its axis. The virtual image formed by the mirror is smaller in size than the object. The nature of the mirror is

1. Plane
2. Concave
3. Convex
4. Concave or convex

Answer: 3. Convex

Question 31. An image that indicates positive magnification is

1.  Erect
2. Inverted
3. Larger than the size of the object
4. Smaller than the size of the object

Answer: 2. Inverted

Question 32. An object is approaching a convex mirror. The ratio of the velocity of the object and that of the object image which is m times magnified is

1. \(-\frac{1}{m^2}\)
2. m²
3. -m
4. \(\frac{1}{m}\)

Answer: 1. \(-\frac{1}{m^2}\)

Question 33. A car is fitted with a convex side-view mirror of a focal length of 20 cm. A second car 2.8 m behind the first car is overtaking the first car at a relative speed 15 m s^-1. The speed of the image of the second car as seen in the mirror of the first one is

1. \(\frac{1}{15} \mathrm{~m} \cdot \mathrm{s}^{-1}\)
2. \(10 \mathrm{~m} \cdot \mathrm{s}^{-1}\)
3. \(15 \mathrm{~m} \cdot \mathrm{s}^{-1}\)
4. \(\frac{1}{10} \mathrm{~m} \cdot \mathrm{s}^{-1}\)

Answer: 1. \(\frac{1}{15} \mathrm{~m} \cdot \mathrm{s}^{-1}\)

Question 34. The image of an extended object, placed perpendicular to the principal axis of a mirror will be erect if 

1. The object and the image are both real
2. The object and the image are both virtual
3. The object is real1but the image in virtual
4. The object is virtual but the image is real

Answer:  3 and 4

v35. If the light moving in a straight line bends by a small but fixed angle, it may be a case of

1. Reflection
2. Refraction
3. Diffraction
4. Dispersion

Answer: 1 And 2

Question 36. Two points P and Q lie on either side of an axis XY. It is desired to produce an image of P at Q using a spherical mirror with XY as the optic axis. The mirror must be

1. Converging
2. Diverging
3. Positioned to the left of P
4. Positioned to the right of Q

Answer:  1 And  3

Question 37. If a converging beam of light is incident on a concave mirror, the reflected light

1. May form a real image
2. Must form a real image
3. May form a virtual image
4. Maybe a parallel beam

Answer:  1, 3, And 4

Question 38. A point object P moves towards a convex mirror with a constant speed V along its optic axis. The speed of the image

1. Is always < V
2. Maybe >, = or < V depending on the position of P
3. Increases as P comes closer to the mirror
4. Decreases as P comes closer to the mirror

Answer: 1 And 3

Question 39. The phenomenon involved in the reflection of radio waves by the ionosphere is similar to

1. The reflection of light by a plane mirrors the total internal
2. Reflection of light in air during a mirage
3. Dispersion of light by water molecules during the formation of a rainbow
4. Scattering of light by particles of air

Answer: 2. Reflection of light in the air during a mirage

Question 40. A car is moving at a constant speed of 60 km h^-1 on a straight road. Looking at the rearview mirror, the driver finds that the car following him is at a distance of 100 m and is approaching at a speed of 5 km h^-1. In order to keep track of the car in the rear, the driver begins to glance alternatively at the rear and side mirror of his car every 2s till the other car overtakes. If the two cars were maintaining their speeds, which of the following statements is correct?

1. The speed of the car in the rear is 65 km hlin
2. The side mirror of the car in the rear would appear to approach with a speed of 5 km h^-1 to the driver of the leading car
3. In the rearview mirror, the speed of the approaching car would appear to decrease as the distance between the cars decreases
4. In the rearview mirror, the speed of the approaching car would appear to decrease as the distance between the cars decreases cars decreases

Answer: 4. In the rearview mirror, the speed of the approaching car would appear to decrease as the distance between the cars decreases cars decreases

Question 41. Rays from the sun subtend an angle θ (in radians) at the pole of a concave mirror of focal length f. If the diameter of the sun is D, the diameter of the image of the sun formed by the mirror is. 

1. Dθ
2. 2 Dθ
3. fθ
4. 2fθ
   

Answer:  3. fθ

If the distance of the sun from the mirror is u,

∴ θ = \(\frac{D}{u}\)

Or, u = \(\frac{D}{u}\)

The rays from the sun form a parallel beam so the image is formed on the focal plane.

So image distance, v= f

Magnification, m= \(\frac{\text { diameter of the image }}{\text { diameter of the sun }(D)}\)

= \(\frac{v}{u}\)

= \(\frac{f}{D / \theta}\)

= \(\frac{f \theta}{D}\)

Hence, the diameter of the image  = D. \(\frac{f \theta}{D}\)

= fθ

Question 42. The ratio of the diameter of the sun to the distance between the Earth and the sun is approximately 0.009.  The approximate diameter of the image of the sun formed by a concave spherical mirror of radius of curvature 0.4 m is.

1. 4.5 × 10^-6m
2. 4.0 ×  10^-6m
3. 3.6×  10^-3m
4. 1.8×  10^-3m

Answer: 4. 1.8×  10^-3m

From the  \(\frac{d}{D}=\frac{f}{x}\)

Or d= \(\frac{f D}{x}\) = 0.009 \(\left(\frac{0.4}{2}\right)\)

= 1.8 × 10^-3 m

Rays from the sun subtend an angle (in radians) at the pole of a concave mirror of focal length f. If the diameter of the sun is D, the diameter of the image of the sun formed by the.

Question 43.  A point source is placed at coordinates (0, 1) in the XY plane. A ray of light from the source is reflected on a plane mirror placed along the X-axis and perpendicular to the XY plane. The reflected ray passes through the point (3, 3). What is the path length of the ray from (0, 1) to ∞

1. 5
2. \(\sqrt{13}\)
3. 2\(\sqrt{3}\)
4. 1+ 2\(\sqrt{3}\)

Answer:  1. 5

The mirror is placed along the X-axis and perpendicular to the XY-plane i.e., the plane of the mirror is XZ-plane.

∴ Coordinate of image P’ of point P(0, 1) =(0,-1)

∴  Distance traversed by light from P(0, 1) to Q(3, 3)

= PR+ RQ = P’R + RQ = P’Q

= \(\sqrt{(0-3)^2+(-1-3)^2}\)

= \(\sqrt{9+16}\)

= 5 unit

Question 44. An object is placed at a distance of 25 cm from a concave mirror and a real image is formed by the mirror at a distance of 37.5 cm.

1. The focal length of the mirror is:

1. 30 cm
2. 45 cm
3. 15 cm
4.  40 cm

Answer: 2. 45 cm

2. If the object is moved 15 cm toward the mirror the image distance will be:

1. 20 cm
2. 25 cm
3. 30 cm
4. 45 cm

Answer: 2. 25 cm

3. The magnification of the image will be:

1. 2 times
2. 5 times
3. 4 times
4. 3 times

Answer:  4. 3 times

Question 45. The focal length of a concave mirror is f. A point object is placed at a distance of xf on the right side of the focus.

1. The image will be formed on the right side of the focus at a distance of:

1. f/ x
2. f+xf
3. 2f/x
4. f-xf

Answer: 1. f/ x

Question 46. A cube of side 2 m is placed in front of a large concave mirror of focal length 1 m in such a way that the face of the cube is at a distance of 3 cm and the face B at a distance of 5 cm from the mirror.

1. The distance between the images of the faces A and B will be

1. 1.5 m
2. 1.75
3. 0.5 m
4. 0.25 m

Answer: 4. 0.25 m

2. The height of the image of the face A will be:

1. 1m
2. 1.5 m
3. 2 m
4. 3m

Answer: 1. 1m

3. The height of the image of the face B will be

1. 1m
2.  0.5 m
3. 1.5 m
4. 3 m

Answer: 2. 0.5 m

Question 47. A concave mirror of radius of curvature 20 cm and a convex mirror of radius of curvature 30 cm are held coaxially face to face at a distance of 40 cm apart. An object of height 5 cm is placed perpendicularly on the common axis at a distance of 15 cm from the concave mirror.

1. If the first reflection occurs in the concave mirror, the final image will be formed at a distance of:

1. 6 cm behind the convex mirror
2. 10 cm behind the convex mirror
3. 4 cm in front of the convex mirror
4. 5 cm in front of the convex mirror

Answer: 1. 6 cm behind the convex mirror

2. The height of the final image will be:

1. 4 cm
2. 5 cm
3. 10 cm
4.  6 cm

Answer: 4. 6 cm

Question 48.  An object is placed at a distance of 40 cm from a concave mirror of a 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

1. 30 cm towards the mirror
2. 3.6 cm away from the mirror
3. 3.0 cm away from the mirror
4. 36 cm towards the mirror

Answer: 2. 3.6 cm away from the mirror

The first case, \(\frac{1}{f}=\frac{1}{v_1}+\frac{1}{u_1}\)

Or, , \(-\frac{1}{15}=\frac{1}{v_1}-\frac{1}{40}\)

[ u₁ = – 40 cm]

Or, v₁ = -24 cm

In 2nd case, \(\frac{1}{f}=\frac{1}{v_2}+\frac{1}{u_2}\)

Or, , \(-\frac{1}{15}=\frac{1}{v_2}-\frac{1}{20}\)

[ u₂ = – 20 cm]

Or, v₂ = -60 cm