CBSE Class 10 Science Light Reflection and Refraction VBQs

Objective Type Questions

Double convex lens: If both the spherical surfaces are bulging outwards, it is called double convex lens. It is thicker at the middle and thinner on edges it is convex lens. Convex lens converges a parallel beam of light, so it is called a converging lens. Double concave lens: If both the spherical surfaces are curved inward, it is called double concave lens. It is a diverging lens. It is thicker one the edges but thinner at the middle.

Question. How will the image formed by a convex lens be affected if the central portion of the lens is blackened ?
(a) No image will be formed by the lens
(b) The central portion of the image will be absent
(c) The full image will be formed but it will be less bright
(d) There will be two images, one due to each exposed portions
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. 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. 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

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

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

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. A student conducts an experiment using a convex lens of focal length 20 cm and an object of height 15 cm. He placed the object at 25 cm from the lens. Can the image be formed on a screen?
(a) yes, because a real image will be formed
(b) no, because a virtual image will be formed
(c) yes, because an erect image will be formed
(d) No because the image is inverted
Answer : A

Question. A student conducts an experiment using a convex lens. He places the object at a distance of 60 cm in front of the lens and observed that the image is formed at a distance of 30 cm behind the lens. What is the power of the lens?
(a) 0.005 dioptre
(b) 0.05 dioptre
(c) 5 dioptre
(d) no, because an inverted image will be formed
Answer : C

Question. A student conducts an activity using a flask of height 15 cm and a concave mirror. He finds that the image formed is 45 cm in height. What is the magnification of the image?
(a) 45 times
(b) 1/ 45 times
(c) 1/ 3 times
(d) 3 times
Answer : D

Question. A mirror and a lens each have 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. Which one of the following statements is true for convex mirrors?
(a) They always give a real, erect, diminished image.
(b) They can produce a parallel beam of light.
(c) They have a wide field of view
(d) They always give a virtual, erect, magnified image.
Answer : C

Question. When will the convex lens give a real image?
(a) Beyond optical centre
(b) Beyond focus
(c) Beyond centre of curvature
(d) Between focus and curvature
Answer : B

Question. What are Concave lenses?
(a) Thicker from the centre than at the edge
(b) Thinner from the centre than at the edge
(c) Thicker from both the positions
(d) Thinner from both the positions
Answer : B

Question. As an object gets closer to the focal point of a convex lens from infinity, its image
(a) Is magnified
(b) Becomes smaller
(c) Becomes closer to the lens
(d) None of these
Answer : A

Study these tables related to refractive index and answer the questions that follow: 

Question. Which of the following has highest refractive index?
(a) Glycerine
(b) Water
(c) Air
(d) Diamond
Answer : D

Question. What happens to ray, when it enters a denser medium from rarer medium?
(a) Ray bends towards the normal
(b) Ray bends away from the normal
(c) Speed of light ray increases
(d) None of the above
Answer : A

Question. Which of the following is correct?
(a) Speed of light in water/Speed of light in air = 1.33
(b) Speed of light in air/Speed of light in water = 1.33
(c) Speed of light in water = 1.33
(d) None of these
Answer : B

Question. What is the speed of blue light in crown glass?
(a) 3 × 10⁸ ms^–1
(b) 1.97 × 10⁸ ms^–1
(c) 4.56 × 10⁸ ms^–1
(d) 3.5 × 10⁸ms^–1
Answer : B

Question. Which of the following is optically denser than water?
(a) Kerosene
(b) Air
(c) Ice
(d) None of these
Answer : A

Is there a relationship between the radius of curvature R and focal length f, of a spherical mirror? For spherical mirrors of small apertures, the radius of curvature is found to be equal to twice the focal length. We put this as R = 2f. This implies that the principal focus of a spherical mirror lies midway between the pole and centre of curvature.

Question. The distance from the pole to focus is called…………
(a) Pole
(b) Aperture
(c) Principal Axis
(d) Focal length
Answer : D

Question. The diameter of the reflecting surface of a spherical mirror is called ………
(a) Aperture
(b) The radius of curvature
(c) Centre of curvature
(d) Pole
Answer : D

Question. The focal length is equal to half of the ………
(a) Axis
(b) Centre of curvature
(c) The radius of Curvature
(d) None of these
Answer : C

Question. Mirrors having a curved reflecting surface are called as:
(a) Plane mirror
(b) Spherical mirrors
(c) Simple mirror
(d) None of the above
Answer : B

Question. The radius of a sphere; of which the reflecting surface of a spherical mirror is a part; is called the………….
(a) Centre of curvature
(b) radius of curvature
(c) Poled
(d) Aperture
Answer : B

The following diagram is of the solar furnace. It is used to generate heat using sun radiation. The solar furnace consists of flat solar tracking heliostat, a parabollic collecting mirror, an attenuator or shutter, and the test zone area. 

Question. Name the Parabolic mirror used in this process
(a) Convex mirror
(b) Plane mirror
(c) Concave mirror
(d) Combination of convex and concave mirror
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

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. 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. What are the types of solar furnaces?
(a) Indirect and concentrating solar power technology
(b) Active and direct
(c) Passive and heliostat
(d) Direct and heliostat
Answer : D

Question. What is solar furnace?
(a) Uses concentrated solar power to produce high temperatures for industry
(b) Uses solar energy to evaporate water and collect it within the same closed system
(c) Uses solar energy to dry substances
(d) Uses solar energy to dry liquids
Answer : A

Question. Select the material that can be used as a heliostat surface to reflect maximum radiation
(a) Ribbon silicon.
(b) Polycrystalline silicon.
(c) Convex mirror
(d) Plane mirror
Answer : D

Question. The device that can control the amount of light entering the furnace
(a) Concentrator
(b) Heliostat
(c) Attenuator
(d) None of the above
Answer : C

The atmosphere reflects, scatters, and absorbs solar radiation, reducing the amount of sunlight that reaches Earth’s surface. Some atomospheric gases absorb specific wavelengths of solar radiation. Water vapour is a strong absorber of incoming infrared energy, causing a significant reduction in the amount of solar radiation reaching the ground during humid conditions. Ozone, during its formation and dissociation, absorbs harmful ultraviolet radiation that can lead to sunburn and skin cancer. Haze, dust, smoke, and air pollutants in general block incoming solar energy to some extent wherever present. Clouds strongly reflect, scatter, and absorb incoming sunlight. High, thin circus absorb some sunlight while dense clouds, if thick enough, can produce almost night time conditions.

Question. The ozone layer absorbs what range of wavelengths of the sun’s radiation?
(a) 0.80 nm – 1.50 nm
(b) 200 nm – 315 nm
(c) 450 nm – 570 nm
(d) 600 nm – 750 nm
Answer : B

Question. What factors affect the amount of solar energy that reaches the earth's surface?
(a) Cloud cover, air pollution,
(b) Latitude of a location,
(c) Time of the year
(d) All of the above
Answer : D

Question. What is solar radiation?
(a) Energy radiated from the sun in all directions
(b) Energy radiated from earth in all directions
(c) Radiation travelling in space
(d) Energy radiated from sun that travels in one direction only
Answer : A

Question. What type of radiation does earth emit?
(a) UV
(b) Visible
(c) Infrared
(d) Longitudinal
Answer : C

Question. Which of the following UV radiations is responsible for causing sun burns and skin cancer?
(a) UV-A
(b) UV-B
(c) UV-C
(d) All of the above
Answer : B

Fill in The Blank

Question. Light is a form of .......... and it travels in a ..........
Answer : energy, straight line

Question. The SI unit of power of a lens is .........
Answer : Dioptre

Question. A ray parallel to the principal axis, after reflection, will pass through the ............
Answer : Principal focus

Question. The angle of incidence is ......... to the angle of reflection.
Answer : Equal

Question. The power of a convex lens is .......... and that of a concave lens is ..........
Answer : Positive, negative

Question. sin i/sin r = μ is called .......... law.
Answer : Snell’s

Question. A concave mirror .......... rays of light, whereas a convex mirror .......... rays of light.
Answer : converges, diverges

Question. A light ray travelling obliquely from a denser medium to a rarer medium bends ......... the normal when it travels obliquely from a rarer to a denser medium.
Answer : Away from, towards

Question. The centre of the reflecting surface of a spherical mirror is a point called the .........
Answer : Pole

Question. A ray of light passes ......... after refraction through the optical centre of a thin lens.
Answer : straight

True/False

Question. When a ray of light travels from air to water, its speeds up.
Answer : False

Question. A plane mirror can form virtual images.
Answer : True

Question. A concave lens will always give a virtual, erect and diminished image.
Answer : True

Question. Light has transverse wave nature.
Answer : True

Question. The incident ray, the normal to the mirror at the point of incidence and the reflected ray, all lie in the same plane.
Answer : True

Question. The refractive index of a transparent medium is the ratio of the speed of light in vacuum to that in the medium.
Answer : True

Question. The reflecting surfaces, of all types, obey the laws of reflection.
Answer : True

Question. An object is placed in front of a mirror and an image of it is formed at the object itself. The mirror mentioned in question is a convex mirror.
Answer : True

Assertion and Reason

DIRECTION : In the following questions, a statement of assertion (A) is followed by a statement of reason (R). Mark the correct choice as:

(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.
(e) Both Assertion and Reason are false.

Question. Assertion : A point object is placed at a distance of 26 cm from a convex mirror of focal length 26 cm. The image will not form at infinity.
Reason : For above given system the equation 1/u + 1/v = 1/ƒ gives n = 3.
Answer : C

Question. Assertion : If the rays are diverging after emerging from a lens; the lens must be concave.
Reason : The convex lens can give diverging rays.
Answer : D

Question. Assertion : Light travels faster in glass than in air.
Reason : Glass is denser than air.
Answer : D

Question. Assertion : Keeping a point object fixed, if a plane mirror is moved, the image will also move.
Reason : In case of a plane mirror, distance of object and Its image is equal from any point on the mirror.
Answer : D

Question. Assertion : When a concave mirror is held under water, its focal length will increase.
Reason : The focal length of a concave mirror is independent of the medium in which it is placed.
Answer : D

Question. Assertion : If both object and plane mirror are moved through a distance x , then the image moves through a distance 2x .
Reason : If object is fixed and plane mirror is moved through a distance x then the image also moves through a distance 2x .
Answer : C

Question. Assertion : If a spherical mirror is dipped in water, its focal length remains unchanged.
Reason : A laser light is focused by a converging lens. There will be a significant chromatic aberration.
Answer : C

Question. Assertion : A ray incident along normal to the mirror retraces its path.
Reason : In reflection, angle of incidence is always equal to angle of reflection.
Answer : A

Question. Assertion : A virtual image cannot be photographed.
Reason : Only real objects are photographed.
Answer : C

Question. Assertion : Large concave mirrors are used to concentrate sunlight to produce heat in solar cookers.
Reason : Concave mirror converges the light rays falling on it to a point.
Answer : A

Question. Assertion : Refractive index has no units.
Reason : The refractive index is a ratio of two similar quantities.
Answer : A

Question. Assertion : The speed of light in glass depends on colour of light.
Reason : The speed of light in glass vg = c/ng the refractive index (ng) of glass is different for different colours.
Answer : A

Question. Assertion : A convex mirror is used as a driver’s mirror.
Reason : Convex mirrors have a wider field of view as they are curved outwards. They also give an erect, though diminished image.
Answer : A 

Question. Assertion : A ray of light incident along the normal to the plane mirror retraces its path after reflection from the mirror.
Reason : 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

Question. Assertion : Higher is the refractive index of a medium or denser the medium, lesser if the velocity of light in that medium.
Reason : Refractive index is inversely proportional to velocity.
Answer : A

Case Study Based Questions:

We know that lenses form different types of images when objects are kept at varying positions. When a ray is incident parallel to the principal axis, then after refraction, it passes through the focus or appears to come from the focus.When a ray goes through the optical centre of the lens, it passes without any deviation. If the object is placed between the focus and optical center of the convex lens, erect and magnified image is formed. As the object is brought closer to the convex lens from infinity to focus, the image moves away from the convex lens from focus to infinity. Also the size of the image goes on increasing and the image is always real and inverted. A concave lens always gives a virtual, erect and diminished image irrespective of the position of the object.

Question. The location of image formed by a convex lens when the object is placed at infinity is
(a) at focus
(b) at 2F
(c) at optical center
(d) betweenFand 2F
Answer : A

Question. The size of image formed by a convex lens when the object is placed at the focus of convex lens is
(a) highly magnified
(b) point in size
(c) small
(d) same as that of object
Answer : A

Question. When the object is placed at the focus of concave lens, the image formed is
(a) real and smaller
(b) virtual and smaller
(c) virtual and inverted
(d) real and erect
Answer : B

Question. When the object is placed at 2F in front of convex lens, the location of image is
(a) at F
(b) between F and optical center
(c) at infinity
(d) none of the above
Answer : D

Very Short Answer Type Questions

Question. Define the principal focus of a concave mirror.
Answer : It is a point on the principal axis where the rays of light parallel to principal axis meet.

Question. Name a mirror that can give an erect and enlarged image of an object.
Answer : Concave mirror.

Question. Find the focal length of a convex mirror whose radius of curvature is 32 cm.
Answer : Radius of curvature R = 32 cm
R = 2f
∴ f = R/2 
= 32/2
= 16 cm.

Question. Draw the given diagram in your answer book and complete it for the path of ray of light beyond the lens.
Answer : 

Question. A ray of light travelling in air enters obliquely into water. Does the light ray bend towards the normal or away form the normal? Why?
Answer : The light bends towards the normal on entry into water because water is optically denser than air.

Question. The refractive index of diamond is 2.42. What is the meaning of this statement?
Answer : As refractive index = speed of light in air / speed of light in diamond
This means the ratio of the speed of light in the air and the speed of light in diamond is equal to 2.42.

Question. A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it.
Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also find the power of the lens.
Answer :
1/v – 1/u = 1/f
v = + 50 cm. Convex lens as image is of same size hence
u = – 50 cm

1/f = 1/ (50 cm)  –   –1/(–50 cm)
= 1/50  +  1/50
= 1/25 cm
f = + 25 cm = + 0.25 m.

Question. The magnification produced by a plane mirror is +1. What does this mean?
Answer : Magnification, m = + 1
 + indicates virtual image.
1 indicates that the object size and image size is same.

Question. A doctor has prescribed a corrective lens of power +1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?
Answer : P = +1.5 D, P = 1/f 
Focal length of the lens f = 1/P = 1/+1.5 D
= + 0.67 m
Power of the lens is +ve, and it is converging lens i.e., convex lens.

Short Answer Type Questions

Question. Redraw the given diagram and show the path of refracted ray.

Answer : 

Question. If a light ray IM is incident on the surface AB as shown, identify the correct emergent ray.

Answer : Q as it has to be parallel to S.

Question. Redraw the given diagram and show the path of the refracted ray.

Answer : 

Question. An object of 2 cm high is placed at a distance of 64 cm from a white screen on placing a convex lens at a distance of 32 cm from the object it is found that a distant image of the
object is formed on the screen. What is the focal length of the convex lens and size of the image formed on the screen? Draw a ray diagram to show the formation of the image in this position of the object with respect to the lens.
Answer : Since the object-screen distance is double of object-lens separation, the object is at a distance of 2f from lens and the image should be of the same size of the object.

So 2f = 32 ⇒ f = 16 cm
Height of image = Height of object = 2 cm

Question. A convex lens has a focal length of 10 cm. At what distance from the lens should the object be placed so that it gives a real and inverted image 20 cm away from the lens?
What would be the size of the image formed if the object is 2 cm high? With the help of a ray diagram show the formation of the image by the lens in this case.
Ans. f = +10 cm, ν = +20 cm as image is real and inverted. Height of the object
= 2 cm (say +ve)
Using 1/f = ν/1 – 1/u, we get