CBSE Class 10 Physics Light Reflection and Refraction MCQs Set J

Question. An incident ray makes 60° angle with the surface of the plane mirror, the angle of its refraction is
(a) 60°
(b) 90°
(c) 30°
(d) 0°

Answer: c

Question. Power of a lens is –40, its focal length is
(a) 4 m
(b) – 40 cm
(c) – 0.25 m
(d) – 25 m.

Answer: c

Question. Which one of the following materials cannot be used to make a lens?
(a) Water
(b) Glass
(c) Plastic
(d) Clay

Answer: d

Questions. When light enters from air to glass, which of the following changes:
A. Wavelength
B. Velocity
C. Frequency
D. Amplitude
(a) A and D
(b) B and C
(c) A and C
(d) A, B and D

Answer: d

Question. The unit of power of lens is
(a) metre
(b) centimeter
(c) diopter
(d) m–1

Answer: c

Questions. A spherical mirror and thin spherical lens - each have a focal length of -15 cm. It is likely that:
(a) The mirror is convex, but the lens is concave.
(b) Both are concave
(c) Both are convex
(d) The mirror is concave, but the lens is convex.

Answer: b

Questions. A student has to do the experiment, on finding the focal length of a given concave mirror, by using a distant object. Out of the following set ups (A, B, C, D) available to her A. a screen, a mirror holder and a scaleB. a mirror holder, a screen holder and a scaleC. a screen holder and a scaleD. a mirror holder and a screen holder
(a) D
(b) C
(c) A
(d) B

Answer: d

Question. The radius of curvature of a mirror is 20 cm the focal length is
(a) 20 cm
(b) 10 cm
(c) 40 cm
(d) 5 cm

Answer: b

Questions. A ray passing through the focus and falling on a convex lens will:
(a) retrace its path
(b) will emerge parallel to principal axis
(c) will emerge through focus on other side
(d) will emerge perpendicular to principal axis

Answer: b

Question. Where should an object be placed in front of a convex lens to get a real image of the size of the object?
(a) At the principal focus of the lens
(b) At twice the focal length
(c) At infinity
(d) Between the optical centre of the lens and its principal focus

Answer: b

Question. The image formed by a concave mirror is observed to be virtual, erect and larger than the object. Where should be the position of the object?
(a) Between the principal focus and the centre of curvature
(b) At the centre of curvature
(c) Beyond the centre of curvature
(d) Between the pole of the mirror and its principal focus

Answer: d

Question. Which of the following lenses would you prefer to use while reading small letters found in a dictionary?
(a) A convex lens of focal length 50 cm.
(b) A concave lens of focal length 50 cm.
(c) A convex lens of focal length 5 cm.
(d) A concave lens of focal length 5 cm.

Answer: c

Question. All the distances in case of spherical mirror are measured in relation to
(a) object to image
(b) the pole of the mirror
(c) the focus of the mirror
(d) the image to the object.

Answer: b

Question. The diameter of the reflecting surface of a spherical mirror is called its
(a) Centre of curvature
(b) R=2f
(c) Aperture
(d) Principal focus.

Answer: c

Question. If a ray of light that is incident on a convex lens is parallel to its principal axis, the refracted ray passes through
(a) F₂
(b) 2F₂
(c) O
(d) Principal axis. 

Answer: a

Question. A convex mirror used for the rear view on an automobile has a focal length of 2.5m. A car is located at a distance of 4m from the mirror.
In the above scenario the sign that should be assigned to f and u is
(a) u positive, f negative
(b) f positive, u negative
(c) f and u are positive
(d) f and u negative 

Answer: b

Question. The mirror that always gives virtual and erect image of the object but image of smaller size than the size of the object is
(a) Plane mirror
(b) Concave mirror
(c) Convex mirror
(d) none of these

Answer: c

Question. Image formed by plane mirror is 
(a) real and erect
(b) real an inverted
(c) virtual and erect
(d) virtual and inverted

Answer: c

Question. The magnification (m) of a lens can be calculated by using the formula
(a) m=-v/u 
(b) m=v/u
(c) m=h¹/h
(d) both b and c 

Answer: d

Question. Convex lens focus a real, point sized image at focus, the object is placed
(a) at focus
(b) between F and 2f
(c) at infinity
(d) at 2f

Answer: c

Question. No matter how far you stand from a mirror, your image appears erect. The mirror is likely to be
(a) plane.
(b) concave.
(c) convex
(d) either plane or convex.

Answer: d

Question. In optics an object which has higher refractive index is called
(a) optically rarer
(b) optically denser
(c) optical density
(d) refractive index

Answer: b

Question. The radius of curvature and focal length of a concave mirror are
(a) positive
(b) negative
(c) both
(d) none of these

Answer: b

Question. The optical phenomena, twinkling of stars, is due to
(a) atmospheric reflection
(b) total reflection
(c) atmospheric refraction
(d) total refraction

Answer: c

Question. In a concave mirror an erect and virtual image is formed when the object is placed
(a) Between C and F
(b) Beyond C
(c) Between P and F
(d) At C

Answer: c

Question. The ratio of the speed of light in vacuum to that in a medium is known as
(a) magnification
(b) refraction
(c) refractive index
(d) Snell’s law

Answer: c

Question. A spherical mirror and a thin spherical lens have each a focal length of –15 cm. The mirror and the lens are likely to be
(a) both concave
(b) both convex
(c) the mirror is concave and the lens in convex.
(d) the mirror is convex but the lens is concave.

Answer: a

Question. Focal length of plane mirror is
(a) at infinity
(b) zero
(c) negative
(d) none of these

Answer: a

Question. A spherical mirror and a thin spherical lens have each a focal length of −15 cm. The mirror and the lens are likely to be
(a) both concave
(b) both convex
(c) the mirror is concave and the lens is convex
(d) the mirror is convex, but the lens is concave 

Answer: a

Question. When a lemon kept in water in a bowl is viewed from outside, it appears ___________ than its actual size.
(a) None of these
(b) Smaller
(c) Larger
(d) Same

Answer: c

Question. The image formed by a concave mirror is observed to be virtual, erect and larger than the object. Where should be the position of the object?
(a) Between the principal focus and the centre of curvature
(b) At the centre of curvature
(c) Beyond the centre of curvature
(d) Between the pole of the mirror and its principal focus.

Answer: d

Question. A mirror that has very wide field view is
(a) concave
(b) convex
(c) plane
(d) none of these

Answer: b

Question. Where should an object be placed in front of a convex lens to get a real image of the size of the object?
(a) At the principal focus of the lens
(b) At twice the focal length
(c) At infinity
(d) Between the optical centre of the lens and its principal focus. 

Answer: b

Question. Which of the following lenses would you prefer to use while reading small letters found in a dictionary?
(a) A convex lens of focal length 50 cm
(b) A concave lens of focal length 50 cm
(c) A convex lens of focal length 5 cm
(d) A concave lens of focal length 5 cm 

Answer: c

Question. The object distance in both concave as well as convex mirror is
(a) negative
(b) positive
(c) zero
(d) none of these

Answer: a

Question. If the object is placed at focus of a concave mirror, the image is formed at
(a) infinity
(b) focus
(c) centre of curvature
(d) between F and O.

Answer: a

Question. The power of a lens is + 1.6 D. The nature of lens is
(a) Convex lens
(b) Concave lens
(c) both concave an convex
(d) none of these

Answer: a

Question. A concave mirror gives, real, inverted and same size image if the object is placed
(a) at F
(b) at infinity
(c) at C
(d) beyond C

Answer: c

Question. A concave mirror gives virtual, erect and enlarged image if the object is placed:
(a) at infinity
(b) between F and C
(c) between P and F
(d) at F.

Answer: c

Question. As incident angle is increased for a given pair of medium, the refraction angle will
(a) decrease
(b) always remains same
(c) may increase or decrease
(d) increase

Answer: d

Question. An object move a distance 'f' between 2f and f of a concave mirror. The image would have travelled a distance of
(a) f/2
(b) ∞
(c) 2f
(d) f

Answer: b

Question. No matter how far you stand from a mirror, your image appears erect. The mirror is likely to be
(a) plane
(b) concave
(c) convex
(d) either plane or convex 

Answer: d

Question. Which one of the following materials cannot be used to make a lens?
(a) Water
(b) Glass
(c) Plastic
(d) Clay 

Answer: d

Question. A student is to find the focal length of a
(i) concave mirror,
(ii) convex lens by using a distant object.
He will observe that the screen is on the same side as the object
(a) in both the cases
(b) in case (ii) but not in case (i)
(c) in case (i) but not in case (ii)
(d) in neither of the two cases

Answer: c

Question. The refractive indices of some media are given below:
Medium   Refractive index
X               1.51
Y               1.72
Z               1.83
W             2.42
In which of these is the speed of light minimum and maximum, respectively.
(a) X-minimum, W-maximum
(b) Z-minimum, W-maximum
(c) W-minimum, X-maximum
(d) X-minimum, Z-maximum

Answer: c

Question. Assertion (A).The value of F in a concave mirror is taken as –ve and in a convex mirror is taken as +ve.
Reason(R). All distances measured to the right of the origin are taken as +ve and those measured along the left of the origin are taken as –ve. 
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true

Answer: a

Question. Assertion (A). 1.33 is the absolute refractive index of water.
Reason (R). Air is optically denser than water. 
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true

Answer: c

Question. Find out, from Table (10.3), the medium having highest optical density. Also, find the medium with lowest optical density. 
Answer: As per table, diamond has highest optical density (2.42). Medium with lowest optical density is air (1.0003)

Question. What is magnification of lens? 
Answer: Magnification of a lens is to the ratio of the height of the image formed by lens to the actual height of object.
If h is the height of the object and h' the height of the image formed by lens, then magnification m = h'/h
If u and v are the distances of object and image
m = h'/h = v/u

Question. Define the term power of a lens. Give its SI unit. State whether the power of a converging lens is positive or negative. 
Answer: Power of a lens is defined as the reciprocal of its focal length f (in metres).
P = 1/f(in m)

 Question. Give the cartesian sign convention for:
a. height of a real image, and
b. height of a virtual image.
Answer: (a) - ve, and (b) + ve.

Question. What is refractive index ? 
Answer: The ratio between the sine of angle of incidence (in air) to the sine of angle of refraction (in a denser medium) is called refractive index.

Question A mirror has magnification 0.4, what type of the mirror is that? and what type of the image is formed ? 
Answer: It is a convex mirror since the magnification is positive as well as less than one. Image is diminished and erect.

Question. How is focal length related to radius of curvature of the mirror ? 
Answer: R = 2 f or f = R/2

Question. Name the mirror that can give an erect and enlarged image of an object.
Answer: When an object is placed between the pole and the principal focus of a concave mirror, the image formed is virtual, erect, and enlarged. 

Questions. What is the unit of refractive index? 
Answer: Refractive index has no units as it is a ratio of two similar physical quantities.

Questions. If the magnification of a body of size 1 m is 2. What is the size of the image? 
Answer: Height of object = h = 1 m
Height of image = h' = ?
Magnification = m = 2
we know that,
m = h'/h
2 = h'/1
h' = 2 m
Height/size of image is 2 m

Questions. How would you decide the medium having highest optical density and medium with lowest optical density?
Answer: Optical density depends upon refractive index. Higher the refractive index, higher the optical density and vice versa.
Diamond (n = 2.42) is having maximum optical density and air (n = 1.0003) is having least optical density.

Question. Why do we prefer a convex mirror as a rear-view mirror in vehicles?
Answer: Convex mirrors give a virtual, erect, and diminished image of the objects placed in front of them. They are preferred as a rear-view mirror in vehicles because they give a wider field of view, which allows the driver to see most of the traffic behind him. 

Question. Find the focal length of a convex mirror whose radius of curvature is 32 cm.
Answer: Radius of curvature, R = 32 cm
Radius of curvature = 2 × Focal length (f)
R = 2f
f = R / 2 = 32 / 2 = 16 cm
Hence, the focal length of the given convex mirror is 16 cm. 

Question. A ray of light travelling in air enters obliquely into water. Does the light ray bend towards the normal or away from the normal? Why?
Answer: The light ray bends towards the normal. When a ray of light travels from an optically rarer medium to an optically denser medium, it gets bent towards the normal. Since water is optically denser than air, a ray of light travelling from air into the water will bend towards the normal.

Question. Define the principal focus of a concave mirror.
Answer: Light rays that are parallel to the principal axis of a concave mirror converge at a specific point on its principal axis after reflecting from the mirror. This point is known as the principal focus of the concave mirror. 

Question. The radius of curvature of a spherical mirror is 20 cm. What is its focal length?
Answer: Radius of curvature, R = 20 cm
Radius of curvature of a spherical mirror = 2 × Focal length (f)
R = 2f
f = R / 2 = 20 / 2 = 10 cm
Hence, the focal length of the given spherical mirror is 10 cm.

Question. Find the power of a concave lens of focal length 2 m.
Answer: Focal length of concave lens, f = 2 m
Power of a lens , P = 1 / f (in meters) = 1 / (-50) = -0.5D
Here, negative sign arises due to the divergent nature of concave lens.
Hence, the power of the given concave lens is −0.5 D. 

Question. An object 5 cm high is placed at a distance of 10 cm from a convex mirror of radius of curvature 30 cm. Find the nature, position and size of the image. 
Answer: Here u = - 10 cm (u is always negative), v = ? 
 f = r/2 = +30/2 or f = + 15cm
f and r for convex mirror are always positive.
Using the formula 1/f = 1/v + 1/u we have 1/15 = 1/v - 1/10 or
1/v = 1/15 + 1/10 = 5/30 v
or ∴ Image is 6 cm behind the mirror (right or mirror).
It is virtual and errect.
Magnification m = - v/u = -(+6)/10 = 0.6
Hence image is 0.6 times the size of the object.
Again m = h₂/h₁ where h₂ is the size of the image and h1 the size of the object.
∴ h₂ = mh₁= 0.6(5)= 3 cm.
Hence image is 3 cm. high.

Question. Name the type of mirror used in the following situations.
(a) Headlights of a car
(b) Side/rear-view mirror of a vehicle
(c) Solar furnace
Support your answer with reason.
Answer: Explanation
(a) Concave mirror is used in the headlights of a car. This is because concave mirrors can produce powerful parallel beam of light when the light source is placed at their principal focus.
(b) Convex mirror is used in side/rear view mirror of a vehicle. Convex mirrors give a virtual, erect, and diminished image of the objects placed in front of it. Because of this, they have a wide field of view. It enables the driver to see most of the traffic behind him/her.
(c) Concave mirrors are convergent mirrors. That is why they are used to construct solar furnaces. Concave mirrors converge the light incident on them at a single point known as principal focus. Hence, they can be used to produce a large amount of heat at that point.