Important Questions Class 10 Science Chapter 10

Important Questions Class 10 Science Chapter 10 – Light Reflection and Refraction

Science allows us to know the truth, supported by evidence and logic. Science has made human life better by massively contributing to the fields of technology, medicine, nutrition, etc. Class 10 Science Chapter 10 deals with two properties of light.

In this chapter, students will study light reflection and light refraction. We know light can act in two ways with an object’s surface. If the object is transparent, light can enter it; ifr  the object is opaque or translucent, the light hits the surface and bounces back. When light moves through a transparent object, its former direction changes depending on the density of the object. This property of light is called refraction. The bouncing back of light from a shiny surface, such as a mirror, is known as reflection. Students must practise questions from the chapter to score better in exams.

Extramarks is a leading company that provides all the important study materials. Our experts know the importance of practise and have made the Important Questions Class 10 Science Chapter 10 to help students in their practise. They have collected the questions from different sources such as the textbook exercise, CBSE sample papers, NCERT exemplar, important reference books, and CBSE past years’ question papers. They have also solved the questions, and experienced professionals have further checked the answers to ensure the best quality of the content. Thus, the Important Questions Class 10 Science Chapter 10 will help students  score better in exams.

Extramarks is a leading company that provides all the study materials related to CBSE and NCERT. You can download the study materials after registering on our official website. We provide CBSE syllabus, CBSE past years’ question papers, CBSE sample papers, CBSE revision notes, CBSE extra questions, NCERT books, NCERT exemplars, NCERT solutions, NCERT important questions, vital formulas, and many more.

CBSE Class 10 Science Important Questions 2022-23

CBSE Class 10 Science Important Questions are also available for the following chapters:

Class 10 Science Chapter 10 Question Answer

Extramarks is a leading company that provides all the important study materials related to CBSE and NCERT. Our experts have created the question series to help students. They collected the questions from different sources, such as the textbook exercises, CBSE past years’ question papers, CBSE sample papers, and important reference books. They have written the answers to help students in practice. Experienced professionals have further checked the solutions to ensure the best standard of answers. Thus, the Important Questions Class 10 Science Chapter 10 will help students  score better in exams. The important questions are:

Question 1. Define the principal focus of concave mirrors.

Answer 1: Principal focus of a concave mirror is the point on the principal axis. At this point, all the incident rays parallel to the principal axis meet or converge after the reflection from the concave mirror.

Question 2: A spherical mirror’s radius of curvature is 20 cm. Calculate the focal length.

Answer 2: f = R/2 = 20/2 = 10 cm.

Question 3: Name a mirror that gives an erect and enlarged image of an object.

Answer 3: This is the concave mirror that gives such an image.

Question 4: Why are convex mirrors preferred in vehicles?

Answer 4: This is because of the following reasons:

• It produces a virtual image.
• The image is erect.
• The size of the image is smaller than the object.

In a small mirror, this view is responsible for providing the driver with a wide field of view.

Question 5: A light ray travels in the air and enters obliquely into water.  Is it bending away from or towards normal?Explain

Answer 5: The ray of light bends toward the normal. The light’s speed is lower in a dense medium compared to a rarer medium. Water has a greater optical density than air.

Question 6. Identify the device used as a spherical mirror or lens in the given cases when the images formed are virtual and erect in the cases given below:

• The object is placed between the device and the focus, and the image is formed behind it and enlarged.

• When the object is placed between the focus and the device, the image is formed on the same side as that of the object, and the image is enlarged.

• The object is placed between the device and infinity, and the diminished image is formed between the focus and the optical centre on the same side as the object.

• The image formed between the pole and focus diminishes when the object is placed between infinity and the device.

Answer 6:

1. Concave mirror
2. Convex lens
3. Concave lens
4. Convex mirror.

Question 7:The pencil dipped in water  appears to be bent at the air and water interface when dipped in water in a glass tumbler. Will the pencil bend if a liquid like kerosene or turpentine is used instead of water? Give a reason for your answer.

Answer 7: No. The refractive index of the liquid in whichthe pencil is dipped is responsible for this.

Refractive index = real depth/apparent depth.

As per this relation, the tip at the bottom will elevate.

Question 8: Sudha finds that a sharp image of the windowpane of her science laboratory is formed from the lens at a distance of 15 cm. Then she tries to focus on the building, which is visible to her outside the window, instead of the windowpane without disturbing the lens. To obtain a sharp image of the building, in which direction will she move the screen? What is the optimal focal length of this lens?

Answer 8: Sudha will move the screen toward the lens so that the final image is in focus. The focal length is less than 15 cm, as the building can be treated as an object at an infinite distance.

Question 9. How is there a relationship between the power and the focal length? There are two lenses with focal lengths of 20 cm and 40 cm, respectively. Which of the following lenses will form more convergent light?

Answer 9: The lens power is the reciprocal of the focal length.

P= 1f in m= 100f in cm

P 20 = 100/20 = 5D.

P 40 = 100/40 = 2.5 D

There will be more convergence in the lens with a focal length of 20 cm.

Question 10. The candle flame image on the screen is obtained from the lens on the other side. When an image is three times the flame size and the distance between the lens and the image is 80 cm, then calculate the distance of the candle placed from the lens. Add a note on the type of the image at a distance of 80 cm and the lens.

Answer 10: 

Since m = hi/ho = v/u for a lens.

Image is real

m = -3 = v/u

v = 80 cm

u = v/-3 = 80/-3 cm

there will be a convex lens

80/3 = 26.6 cm, which shows that the candle is placed at a distance of 26.6 cm to the left of the convex lens so that a real image is formed at 80 cm distance on the right side of the lens.

Question 11. Draw the images for the following AB object with suitable rays:

Answer 11:

The following image is formed when the object is kept between the pole and the focus point of the concave mirror.

In the given diagram, the object is placed between the centre of curvature C and the focus point F. Image of object AB can be obtained as

In the diagram given below, the object is placed at the centre of the curvature of a concave mirror. The image formed is given below.

Question 12. List the image characteristics formed by plane mirrors.

Answer 12: The image formed by the plane mirror has the following characteristics:

• Image distance and object distance are equal.
• Virtual and erect image is formed.
• The size of the image and the object are equal.
• The image formed is laterally inverted.

Question 13: What are the laws of reflection of light?

Answer 13: The law of reflection states that:

• The angle of incidence is equal to the angle of reflection.
• The incident  reflected rays are normal to the mirror.The point of incidence is in the same plane.

Question 14. A student projected a candle flame image on a screen which is 48 cm in front of the mirror, by placing the flame 12 cm from its pole.

• Suggest the type of mirror which should be used.

• Find the linear magnification of the image produced.

• How far is the image from the object?

• Diagrammatic presentation of the image

Answer 14:

1. The type of mirror used should be a concave mirror.
2. Linear magnification is calculated as follows:

m = -v/u = -(-48)/-12 = -4

1. To calculate the distance between the image and the object

= 48 – 12 = 36 cm

Question 15. What is an optical centre?

Answer 15: 

The optical centre is the central part of any lens through which a ray of light will pass without any deviation. It is represented by the letter O.

Question 16. Why does a light ray bend when it travels from one medium to another?

Answer 16: A ray of light bends when it travels from one medium into another because of the change in speed of light to another.

Question 17. What is the refractive index of diamonds, and what does that indicate?

Answer 17: The refractive index of diamonds is 2.42. This indicates that the speed of light in a vacuum, as compared to the speed of light in a diamond, is 2.42.

Question 18. State the type of mirrors used for

• Headlight

• Rearview mirror

Answer 18:

1. To get powerful beams of light, concave mirrors are used in the headlights.
2. Convex mirrors are used as rear view mirrors of the vehicle to get a wider field of view and erect an image of traffic behind.

Question 19. Why is a concave mirror used as a shaving mirror?

Answer 19: The concave mirror is used for shaving because

• The images produced are erect when the mirror is close to the face.
• It also provides an enlarged view of the face so that a person can shave safely.

Question 20. What types of mirrors are used in the design of solar furnaces? Explain how these devices attain a high temperature.

Answer 20: Concave mirrors are used in solar furnace design. When a solar furnace is kept at the focus point of a large concave mirror, it focuses a parallel beam of light on the surface of the furnace. So, a very high temperature is attained at the focus point after some time.

Question 21. A spherical mirror produces a magnification of  -3. What information did you get about the mirror and image in this case?

Answer 21: The negative sign of magnification demonstrates that the image is real but inverted. Since the image is real but inverted, the mirror is concave, and a magnification of -3 suggests that the image is magnified.

Question 22. Do big shopping stores use mirrors to watch the customer’s activities?

Answer 22: Convex mirrors are used in big shopping stores to manage customers’ activities.

Question 23. Multiple choice questions:

1. Which is not used for making a lens?

• Water

• Glass

• Plastic

• Clay

Answer 1: (d) Clay

Explanation:

Clay can never be used to make a lens, as it does not allow light to pass through it.

2. What should be the object’s position for the image formed by the concave mirror to be erect, virtual, and larger than the object?

• The object should be between the principal focus and the centre of curvature.

• At the centre of curvature

• Beyond the centre of curvature

• Between the pole of the mirror and the principal focus.

Answer : (d) between the pole of the mirror and the principal focus.

Explanation:

The image formed by the concave mirror will be erect, virtual, and larger than the object.

3. To get a real image of the object’s size, where should you place the object in front of a convex lens?

• At the principal focus of the lens.

• At twice the focal length

• At infinity

• Between the optical centre of the lens and the principal focus

Answer: (b) At twice the focal length

Explanation:

When an object is placed at twice the focal length of the convex lens, the image is formed at twice the focal length on the other side of the lens.

4. In front of a plane mirror, an object is kept at a distance of 0.25 m. The distance between the image and the object will be

• 0.25 m

• 1.0 m

• 0.5 m

• 0.125 m

Answer : (c

Explanation:

Distance between the object and image = 0.25 + 0.25 = 0.5 m

5. 5. Which mirror is used by the dentist to examine the oral cavity?

• Convex mirror

• Plane mirror

• Concave mirror

• Combination

Answer: c)

Explanation:

Concave mirror forms enlarged and erect images when it is held close to the cavity.

6. A divergent lens will produce

• Always a real image,

• Always a virtual image

• Both real and virtual images

• None of these

Answer : (b)

Explanation: this will always form a virtual, erect, and diminished image.

7. Magnification produced by a rearview mirror fitted in vehicles

• Is less than one

• Is more than one

• It is equal to one

• It can be more or less than one depending on the position of the object in front of it.

Answer: (a) Is less than one

Explanation:

The convex mirror, used as a rearview mirror, forms virtual, erect and diminished images and hence the actual object is always much bigger than the image. 

8. A full-length image of a distant tall building can definitely be seen by using

• A concave mirror

• A convex mirror

• A plane mirror

• Both concave and plane mirrors.

Answer : (b)

Explanation:

Convex mirrors have a wide field view.

9. The laws of reflection hold good for

• Plane mirror only

• Concave mirror only

• Convex mirror only

• All mirrors, irrespective of their shape.

Answer : (d)

Explanation:

Any smooth surface, irrespective of the shape, holds good for laws of reflection.

Question 24: State whether true or false

• The angle of refraction cannot exceed 90 degrees.

• When incident angle i satisfies n = 1/sin i, the refracted light will pass along the surface.

• A person standing in front of the mirror finds the image larger than himself. This shows that the mirror is convex.

• Lateral displacement will increase with the thickness of the given slab

• Lateral displacement is directly proportional to the thickness of the glass slab.

• The nature of the image formed by the mirror gives an idea about the nature of the mirror.

• A convex and concave lens of equal focal length normally behaves like a regular glass slab receiving light.

• Concave lenses and convex mirrors diverge the rays, which fall parallel to the principal axis.

• The power of a concave lens is positive.

Answer 29:

1. True
2. True
3. False. The convex mirror always forms a diminished image.
4. True
5. True
6. True
7. False
8. True
9. False 

Question 25. Identify the mirror’s nature and mention two image characteristics formed when the magnification is +6.

Answer 25. This means that the image is formed on the concave mirror. The characteristics of the image are

• Six times, an enlarged image is formed.
• The image formed is virtual and erect.

Question 26. Explain the following terms:

• Optical centre,

• Aperture

• Focal length

Answer 26:

1. The centre of the point of a lens is called the optical centre. It is always present inside the lens. Any light beam that passes through the optical centre emerges without deviation after refraction.
2. The aperture is the length of the lens through which refraction occurs.
3. The distance between the principal focus and the optical centre of the spherical lens is called the lens’s focal length.

Question 27. We use two light rays to construct a ray diagram, so it is easy to know their directions after refraction from the lens. List the two rays and state the ray’s path after refraction. Use them to locate the image of an object between f and 2f of a convex lens.

Answer 27. The two rays are:

• A ray of light from the object that is parallel to the principal axis, after refraction from a convex lens, passes through the principal focus on the other side of the lens, and, in the case of a concave lens, a ray appears to diverge from the principal focus located on the same side of the lens.
• A ray of light passing through the optical centre of a lens will emerge without any deviation.

• When the object is placed between F and 2F

Question 28. What is magnification by a plane mirror?

Answer 28: Magnification is formed by a plane mirror in unity. In plane mirrors, the size of any image formed is equal to the size of the object.

Question 29. List the characteristics of an image formed by plane mirrors.

Answer 29: The characteristics of the image by a plane mirror are:

• A plane mirror always forms an erect, virtual, size-to-size image at the same distance as the object but at the back of the mirror.
• Magnification is +1
• It forms a laterally inverted image.
• When the angle of ϴ tunes a plane mirror, the reflected ray will turn by the angle of 2ϴ
• The curvature radius of a  plane mirror is infinity. Its focal length is, therefore, infinity.
• To see the full image of a person, he needs a mirror whose length is half his height.

Question 30: Construct a ray diagram using two rays chosen to know their directions after mirror reflection. Locate the image of an object placed between the pole and the focus of a concave mirror.

Answer 30:

The two light rays whose path of reflection are priorly known as

• When the incident ray gets reflected in the same way, it is due to its passage through the centre of curvature of a concave mirror.
• When the incident ray is oblique to the principal axis, toward the mirror pole, it is reflected by making equal angles with the principal axis. This is the law of reflection.

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Practice is very important for students. It helps them  build knowledge and boost their confidence. The textbook exercises have limited questions, which are insufficient for students, and they must take help from other books to score better in exams. Our experts have made the question series to help students solve questions, and there will be multiple benefits to solving the question series. The benefits of solving the Important Questions Class 10 Science Chapter 10 are-

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Extramarks is a leading company that provides all the important study materials related to CBSE and NCERT. You can download the study materials after registering on our official website. We provide CBSE syllabus, CBSE revision notes, CBSE extra questions, CBSE sample papers, CBSE past years’ question papers, NCERT books, NCERT solutions, NCERT important questions, vital formulas, NCERT exemplars, and many more. Like the Important Questions Class 10 Science Chapter 10, you will also find important questions for other chapters. Click on the links below to download the study materials.

• NCERT books
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