CBSE Class 10 Physics Light Reflection And Refraction Worksheet Set C

Multiple Choice Questions

Question. A student obtains a blurred image of a distant object on a screen using a convex lens. To obtain a distinct image on the screen he should move the lens
(a) away from the screen
(b) towards the screen
(c) to a position very far away from the screen.
(d) either towards or away from the screen depending upon the position of the object.
Answer: (d)

Question. A student very cautiously traces the path of a ray through a glass slab for different values of the angle of incidence (\(\angle i\)). He then measures the corresponding values of the angle of refraction (\(\angle r\)) and the angle of emergence (\(\angle e\)) for every value of the angle of incidence. On analysing these measurements of angles, his conclusion would be :
(a) \(\angle i > \angle r > \angle e\)
(b) \(\angle i = \angle e > \angle r\)
(c) \(\angle i < \angle r < \angle e\)
(d) \(\angle i = \angle e < \angle r\)
Answer: (b)

Question. Three students A, B and C focussed a distant building on a screen with the help of a concave mirror. To determine focal length of the concave mirror they measured the distances as given below :
Student A : From mirror to the screen
Student B : From building to the screen
Student C : From building to the mirror
Who measured the focal length correctly ?
(a) Only A
(b) Only B
(c) A and B
(d) B and C
Answer: (a)

Question. A student has focussed on the screen a distant building using a convex lens. If he has selected a blue coloured building as object, select from the following options the one which gives the correct characteristics of the image formed on the screen.
(a) Virtual, erect, diminished and green shade
(b) Real, inverted, diminished and in violet shade
(c) Real, inverted, diminished and in blue shade
(d) Virtual, inverted, diminished and in blue shade
Answer: (c)

Match the following

Question. Match the following
Column I Column II
(a) Shaving mirror (i) Convex mirror
(b) Diverging lens (ii) Concave lens
(c) Converging lens (iii) Concave mirror
(d) Shop security mirror (iv) Convex lens
Answer: (a) (iii), (b) (ii), (c) (iv), (d) (i).

Fill in the blanks

Question. Fill in the blanks
(a) The ratio of speed of light in vacuum to the speed of light in a medium is called ................... .
(b) When a ray of light travelling in glass enter into water. It is refracted .................. the normal.
(c) A .................. is used as a rear-view mirror.
Answer: (a) Refractive index, (b) away from, (c) diverging mirror.

Very Short Answers Type Questions

Question. Where is the image formed when an object is at large distance from a concave mirror ?
Answer: The image formed is at the focus of the mirror.

Question. What kind of image can be obtained on the screen ?
Answer: Real image.

Question. Which metal is the best reflector of light ?
Answer: Silver metal is the best reflector of light.

Question. What is the nature of the image formed by a concave mirror if the magnification produced by the mirror is + 2 ?
Answer: Virtual and erect.

Question. Between which two points of a concave mirror should an object be placed to obtain a magnification of – 2 ?
Answer: Between F and C.

Question. An object is placed 75 cm from a converging lens of focal length 25 cm. What is the nature of the image ?
Answer: The image is real, inverted and diminished as the object is placed beyond 2f.

Question. Define the term angle of refraction.
Answer: The angle between the refracted ray and the normal at the point of incidence is called angle of refraction.

Question. Define the term angle of incidence.
Answer: The angle between an incident ray and the normal at the point of incidence is called angle of incidence.

Question. What is absolute refractive index ?
Answer: Refractive index of a medium with respect to vacuum is called absolute refractive index.

Question. What is relative refractive index ?
Answer: Refractive index of a medium with respect to another medium is called relative refractive index.

Question. Define power of a lens.
Answer: The power of a lens is a measure of the degree of convergence or divergence of light rays falling on it. It is also defined as the reciprocal of its focal length in metres.

Question. Write two different uses of concave mirrors.
Answer: The concave mirror is used as a shaving mirror and headlights of vehicles.

Question. List four characteristics of the images formed by plane mirrors.
Answer:

• (a) Size of the image is equal to the size of object.
• (b) Formed image is erect.
• (c) Image formed by plane mirror is virtual.
• (d) Formed image is laterally inverted.

Question. Why is convex mirror used as a rear view mirror in vehicles ? State any one reason.
Answer: Convex mirror is used as a rear view mirror in vehicles because it gives a wider field view of the approaching traffic.

Question. State two laws of reflection of light.
Answer: Two laws of reflection of light are :
(a) The incident ray, the normal to the mirror at the point of incidence and the reflected ray, all lie in the same plane.
(b) The angle of incidence is equal to the angle of reflection.

Question. Define the term principal axis of a spherical mirror.
Answer: A straight line passing through the pole of spherical mirror and joining it to the centre of curvature of the mirror is known as the principal axis of the spherical mirror.

Question. State two laws of refraction of light.
Answer: Two laws of refraction of light are :
(a) The incident ray, the refracted ray and the normal to the interface of two transparent medium at the point of incidence, all lie in the same plane.
(b) The ratio of sine of angle of incidence to the sine of angle of refraction is a constant, for the light of a given colour and for the given pair of medium.

Short Answers Type Questions

Question. The absolute refractive index of Ruby is 1.7. Find the speed of light in Ruby. The speed of light in vacuum is \( 3 \times 10^8 \text{ m/s} \).
Answer: We know that,
Refractive index of Ruby (\(\mu\)) = \( \frac{\text{Speed of light in air (or vacuum)}}{\text{Speed of light in Ruby}} \)
So, \( 1.70 = \frac{3 \times 10^8}{\text{Speed of light in Ruby}} \)
or speed of light in Ruby = \( \frac{3 \times 10^8}{1.7} \text{ ms}^{-1} \)
= \( 1.76 \times 10^8 \text{ ms}^{-1} \)
Thus, speed of light in Ruby is \( 1.76 \times 10^8 \text{ ms}^{-1} \).

Question. A 10 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 12 cm. The distance of the object from the lens is 18 cm. Find the nature, position and size of the image formed.
Answer: Given : Height of object, \( h_1 = + 10 \text{ cm} \).
Focal length, \( f = + 12 \text{ cm} \).
Object distance, \( u = – 18 \text{ cm} \).
From the lens formula, \( \frac{1}{v} - \frac{1}{u} = \frac{1}{f} \)

Question. (a) What is an optical medium ? (b) What do you mean by : (i) an optically dense medium ? (ii) an optically rare medium ?
Answer: (a) A medium through which light can travel is called an optical medium. (b) (i) While passing from one medium to the other, if the speed of light slows down, then the second medium is said to be optically denser than the first medium. (ii) While passing from one medium to the other, if the speed of light increases, then the second medium is said to optically rarer than the first medium.

Question. (a) State the two laws of reflection of light. (b) A light ray is incident normally on a plane mirror. What is its angle of incidence ?
Answer: (a) The two laws of reflection are : (i) The incident ray, the reflected ray and the normal at the point of incidence, lie in the same plane. (ii) The angle of incidence is equal to the angle of reflection \( (\angle i = \angle r) \). (b) The angle of incidence will be \( 0^\circ \).

Question. Define the following terms related to spherical mirrors : (a) Centre of curvature, (b) Pole and (c) Aperture.
Answer: (a) The centre of curvature of a spherical mirror is the centre of the sphere of which the mirror is a part. (b) The pole of a spherical mirror is the geometric centre of the spherical surface of the mirror. (c) The plane surface area of the mirror through which the light rays enter and fall on the mirror is called its aperture.

Question. (a) What is meant by magnification ? Write its expression. (b) What is its sign for (i) real, (ii) virtual image ?
Answer: (a) The ratio of height of the image to the height of the object is called linear magnification. If the height of the image is ‘I’ and that of the object is ‘O’, then the magnification ‘m’ is :
\( m = \frac{I}{O} \)
(b) (i) For a real image, magnification is negative. (ii) For a virtual image, magnification is positive.

Question. (a) Define lateral shift. (b) State and explain the factors on which it depends.
Answer: (a) The perpendicular distance between the path of emergent ray and the direction of incident ray is called lateral shift. (b) Lateral shift depends on the following factors : (i) It is directly proportional to the thickness of glass slab. (ii) It is directly proportional to the angle of incidence. (iii) It is directly proportional to the refractive index of the glass slab. (iv) It is inversely proportional to the wavelength of the light used.

Question. Write the relationship between the S.I. unit of the power of a lens and S.I. unit of focal length.
Answer: Reciprocal of focal length of a lens, expressed in metre, is called the power of that lens. Its S.I. unit is 1 dioptre (1 D), where \( 1 \text{ D} = 1 \text{ m}^{-1} \).

Assertion and Reasoning Based Questions

Directions : In the following questions, a statement of assertion is followed by a statement of reason. Mark the correct choice as :
(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true, but reason is not the correct explanation of assertion.
(c) If assertion is true, but reason is false.
(d) If assertion is false but reason is true.

Question. Assertion : The nature of the image formed by a concave mirror is real and inverted.
Reason : The image formed by a concave mirror depends on the position of the object at infinity.

Answer: (a)

Question. Assertion : Convex mirror are used for rear view on vehicles.
Reason : The size of the image formed by a convex mirror will be same.

Answer: (c)

Question. Assertion : A ray of light that travels obliquely from one transparent medium into another will change its direction in the second medium.
Reason : Refraction is due to change in the speed of light as it enters from one transparent medium to another.

Answer: (a)

Question. Assertion : The refractive index of Kerosene is 1.44 which is optically denser than water.
Reason : The mass density of kerosene is lesser than water.

Answer: (b)

Question. Assertion : The sequence of rainbow colour is represented as VIBGYOR.
Reason : Formation of VIBGYOR sequence colour is due to the dispersion of white light.

Answer: (a)

Creating Based Questions

Question. Using the following information form a pathway showing the reflection of a spherical mirror. And also include information that is not mentioned below to complete it. Reflecting surface, spherical mirror, curved inwards, curved outwards, pole, centre of curvature.
Answer: Spherical mirror reflections → curved inwards or outwards. The reflecting mirrors → are curved inwards → called concave mirror. The reflection surface → of convex mirror → is curved outwards. Pole is the centre of reflecting surface. The centre of spherical mirror → known as centre of curvature.

Question. Using the following information form a pathway showing the formation of image by a convex mirror. And also include information that is not mentioned below to complete it. Convex, Infinity, position of image, size of image, Nature of image, between infinity and pole.
Answer: Two positions of objects → considered in the formation of image → by a convex mirror.
Position 1 : The position of object → at infinity → position of image is at the focus of F behind the mirror, size of the image is → highly diminished and point sized. The nature of image is → virtual and erect.
Position 2 : The position of object → between infinity and pole P → displays the image position between → P and F behind the mirror. Size of the image → is diminished. Nature of the image is → virtual and erect.

Question. Using the following information form a pathway showing the process of magnification in spherical mirror. And also include information that is not mentioned below to complete it. Magnification, spherical mirror, object image, ratio, height of image, positive, negative.
Answer: The spherical mirror magnifies → objects image to a relative extent with respect to object size. It is the ratio of → height of image → to the height of object. The positive sign in magnification value → denotes the virtual image. The negative sign in magnification value denotes → real image.

Question. Using the following information form a pathway showing the representation of an image in a spherical mirror. And also include information that is not mentioned below to complete it. Ray, centre of spherical mirror, reflection, light rays, reflecting surface.
Answer: In both concave and convex mirror → for the ray passing through the centre of curvature → the reflection is along same path. The reflection of light rays → is along same path → since the rays incident on the mirror → is normal to the reflecting surface.

Question. Using the following information form a pathway defining refractive index. And also include information that is not mentioned below to complete it. Ray of light, second medium, refractive index, speed, media, air.
Answer: The refractive index → is the extent of change in direction → in second medium of given media pair. The propagation of light travels → with different speed in different media. The speed of light in air is → comparatively less when compared to vacuum.

Paragraph/Table and Case Study Based Questions

Light is a form of energy that produces in us the sensation of sight. Reflection of light is the phenomenon of bouncing back of light in the same medium on striking the surface of any object. The two laws of reflection are the incident ray, the reflected ray and the normal (at the point of incidence), all lie in the same plane and the angle of reflection (r) is always equal to the angle of incidence (i). Refraction of light is the phenomenon of change in the path of light in going from one medium to another.

Question. Mirage is caused due to.............
(a) total Internal Reflection of light by the various layers of air
(b) illusion of the presence of water
(c) result of refraction of light from a non-uniform medium
(d) during sunny days when driving on a roadway
Answer: (a)

Question. What is mirage?
(a) Depends on the position of object
(b) Mirror is concave and the lens is convex
(c) Goes straight into the second medium
(d) Optical illusion caused due to total Internal Reflection
Answer: (d)

Question. What are the two types of mirage?
(a) Thin mirage and thick mirage
(b) Inferior mirage and superior mirage
(c) Intense mirage and diminished mirage
(d) Light mirage and dark mirage
Answer: (b)

Question. How a mirage is formed?
(a) Between focus and centre of curvature
(b) Is formed away from the normal
(c) Illusion of the presence of water and is a result of refraction of light from a non-uniform medium
(d) Is reflected along the same path
Answer: (c)

Question. Mirage is observed mainly during ............... days.
(a) Sunny
(b) Winter
(c) Spring
(d) Hot
Answer: (a)

Rear view mirror is a device that allows the driver to see rearward. It usually finds its place at the top of windscreen in side the cabin. This device is one of the most basic but essential safety devices in the vehicle. It provides assistance to the driver during overtaking, parking in reverse gear etc. Generally, vehicles also have a pair of mirrors attached to the body from outside. They are popular as ‘side mirrors’ or Outer Rear View Mirrors (ORVM) which serve the same purpose. Almost all modern cars mount their side mirrors on the doors-normally at A-pillar rather than the wings (the portion of the body above the wheel well).

Question. An object at a distance of +15 cm is slowly moved towards the pole of a convex mirror. The image will get...
(a) shortened and real
(b) enlarged and real
(c) enlarge and virtual
(d) diminished and virtual
Answer: (d)

Question. A convex mirror is used:
(a) by a dentist
(b) for shaving
(c) as a rear view mirror in vehicles
(d) as a light reflector for obtaining a parallel beam of light
Answer: (c)

Question. The word ‘AMBULANCE’ is written on the vehicle as:
(a) CNALUBMA
(b) ECNALUBMA
(c) AMBULANCE
(d) None of these
Answer: (b)

Question. Mark the correct statement:
(a) Convex mirror conform images of objects spread over a large area.
(b) Convex mirrors are used by dentist.
(c) In convex mirror image is formed larger in size, erect and real.
(d) Convex mirror forms real image.
Answer: (a)

Binoculars, like telescopes, produce, magnified images of faraway objects. Figure shows a typical binocular design. Each side of the binoculars is like a small telescope: light enters a convex objective lens, which inverts the image. The light then travels through two prisms that which is used to completly reflect the incoming ray to invert the image again, so that the viewer sees an image that is upright compared to the object.

Question. Binocular is basically a:
(a) microscope
(b) telescope
(c) dispersion device
(d) magnifying glass
Answer: (b)

Question. Prisms are used in binoculars:
(a) for reflection
(b) for refraction
(c) for dispersion
(d) for total internal reflection
Answer: (d)

Question. Binoculars are used to see:
(a) near objects
(b) far objects
(c) both near and far obejct
(d) none of these
Answer: (b)

Question. Refractive index of air is:
(a) 1.00
(b) 0.5
(c) 1.5
(d) 2.0
Answer: (a)

Question. The lens facing object in binocular is called:
(a) object lens
(b) objective lens
(c) intermediate lens
(d) eye lens
Answer: (b)

Difference between real and virtual image

1. Real Image: When rays of light after reflection meet at a point, real image is formed. Virtual Image: When rays of light after reflection do not meet at a point but appears to meet at a point, virtual image is formed.
2. Real Image: Real image can be obtained on a screen. Virtual Image: Virtual image cannot be obtained on a screen.
3. Real Image: Real image is formed in front of a mirror. Virtual Image: Virtual image is formed behind the mirror.
4. Real Image: Real image is always inverted. Virtual Image: Virtual image is always erect (i.e., upright)

Question. (a) When is an image called ‘real’ ?
(b) When is an image called ‘virtual’ ?
(c) A diminished virtual image can be formed only in
(i) Plane mirror
(ii) A concave mirror
(iii) A convex mirror
(iv) Concave-parabolic mirror
(d) A virtual image larger than the object can be obtained by.
(i) Concave mirror
(ii) Convex mirror
(iii) Plane mirror
(iv) Concave lens
Answer: (a) When the image can be taken on a screen.
(b) When the image cannot be taken on a screen.
(c) (iii) A convex mirror.
(d) (iv) Concave lens.

Archives

Question. Name the type of mirrors used in the design of solar furnaces. Explain how high temperature is achieved by this device.
Answer: Concave mirrors are used. They reflect parallel rays of sunlight and converge them to a single point called the focus, where intense heat is generated, achieving high temperature.

Question. The image of an object formed by a mirror is real, inverted and is of magnification – 1. If the image is at a distance of 40 cm from the mirror, where is the object placed ? Where would the image be if the object is moved 20 cm towards the mirror ? State reason and also draw ray diagram for the new position of the object to justify your answer.
Answer: Since \( m = –1 \), the object is at the centre of curvature (2f). Image distance \( v = –40 \text{ cm} \), so \( u = –40 \text{ cm} \). The focal length \( f = 20 \text{ cm} \). If moved 20 cm towards mirror, the object is now at \( u = –20 \text{ cm} \), which is the principal focus (F). The image will be formed at infinity. Reason: Rays from an object at the focus become parallel after reflection.

Question. It is desired to obtain an erect image of an object, using concave mirror of focal length of 12 cm.
(a) What should be the range of distance of an object placed in front of the mirror ?
(b) Will the image be smaller or larger than the object ? Draw ray diagram to show the formation of image in this case.
(c) Where will the image of this object be, if it is placed 24 cm in front of the mirror ? Draw ray diagram for this situation also to justify your answer. Show the positions of pole, principal focus and the centre of curvature in the above ray diagrams.
Answer: (a) The range should be between 0 cm and 12 cm from the pole (within focal length).
(b) The image will be larger (magnified). [Ray diagram shows object between P and F, rays diverging behind the mirror to meet at a virtual point].
(c) If placed at 24 cm (\( u = 2f \)), the image will be at 24 cm (\( v = 2f \)), real, inverted and same size. [Ray diagram shows object at C, rays reflecting to meet at C].

Question. (a) Define optical centre of a spherical lens.
(b) A divergent lens has a focal length of 20 cm. At what distance should an object of height 4 cm from the optical centre of the lens be placed so that its image is formed 10 cm away from the lens. Find the size of the image also.
(c) Draw a ray diagram to show the formation of image in above situation.
Answer: (a) The central point of a lens through which a ray of light passes without any deviation is called the optical centre.
(b) Given: \( f = –20 \text{ cm} \), \( v = –10 \text{ cm} \), \( h_1 = 4 \text{ cm} \).
Using \( \frac{1}{v} - \frac{1}{u} = \frac{1}{f} \implies \frac{1}{u} = \frac{1}{v} - \frac{1}{f} = \frac{1}{-10} - \frac{1}{-20} = \frac{-2 + 1}{20} = –\frac{1}{20} \).
So, \( u = –20 \text{ cm} \).
Size of image \( h_2 = \frac{v}{u} \times h_1 = \frac{-10}{-20} \times 4 = 2 \text{ cm} \).
(c) [Ray diagram shows object at 2f, image formed between F and O on the same side].