 # RBSE Class 8 Science Chapter 14 Refraction of Light Solutions

In RBSE Class 8 Science Chapter 14 Refraction of Light, students learn about how light travels through different mediums and various lenses. Here, we bring you the important questions and solutions of this chapter that will help students to build a solid foundation and understanding of all important topics listed and master it rigorously.

The solutions that we have provided cover all the key explanations of important questions of RBSE Class 8 Science, according to different chapters. We are hopeful that students can benefit from these solutions and discover fresh concepts while prepping up for the RBSE Class 8 2020 exam.

All the important textbook questions have been solved, and we’ve added a few more additional questions with solutions of the RBSE Class 8 Science for Chapter 14 Refraction of Light from the RBSE Class 8 Science Syllabus. Students can practice from these questions to have an in-depth understanding and thorough knowledge of the chapter. They can also revise from these solutions just before the exams and score good marks in the exams.

## Rajasthan Board Class 8 Science Chapter 14: BYJU’S Important Questions & Answers

### Multiple Choice Questions (MCQs)

Question 1: Which of the following events is not related to refraction of light?

(a) The bottom of water

(b) Appearance of sun before sun rising and after sunset

(c) Formation of image by mirror

(d) Twinkling of stars

Answer: (c) Formation of image by mirror

Question 2. Which is not a part of a human eye?

(a) Retina

(b) Cornea

(c) Pupil

(d) Mid plane

Question 3: When a ray of light enters into a rarer medium from denser medium. Then it bends:

(a) Away from normal

(b) Towards normal

(c) Move in a straight line without deviation.

(d) None of the above

Fill in the blanks with suitable words:

Question 4: _______________of eye control the amount of light enter into the eye.

Question 5: The image formation by the _____________ lens is always erect, virtual and small.

Question 6: Light ray enters into water medium from air bends______________ the normal.

Match column A with B:

 Column A Column B Q7: Liquid filled in between lens and cornea (a) Vitreous humour Q8: Transparent liquid filled in between lens and retina (b) Iris Q9: Muscular structure of dark colour behind the cornea (c) Retina Q10: The portion of eye on which image is formed (d) Eye fluid

 Column A Column B A7: Liquid filled in between lens and cornea (a) Eye fluid A8: Transparent liquid filled in between lens and retina (b) Vitreous Humour A9: Muscular structure of dark colour behind the cornea (c) Iris A10: The portion of eye on which image is formed (d) Retina

### Short Type Answer Textbook Questions

Question 1: What is refraction? What is the cause of refraction?

Answer: When a ray of light enters from one medium to another, then it deviates from its actual path. This phenomenon is called refraction of light.

Cause of Refraction: The speed of light in denser medium i.e, glass is less in comparison to rarer medium i.e, air. This implies that when light enters in a denser medium from a rarer medium, it’s speed slows down. On the contrary, when light enters from a denser medium to a rarer medium, it’s speed accelerates. Hence, refraction of light is a phenomenon which happens due to the difference in speed while travelling from one medium to another.

Question 2: Write the main difference between convex and concave lens.

Answer: Convex lens: A lens which is thicker in the middle part and thinner at the edges is known as Convex lens. A convex lens converts all the parallel beams of light into a single point. The parallel rays which enter through the convex lens meet at a single point and for this reason are also called Converging lens. The incident rays which are parallel to the principal axis get focused on it at a point after refracting from the convex lens, that is known as the focal point of the convex lens.

Concave lens: A lens which is thinner in the middle part and thicker at the edges is known as Concave lens. This lens diverges the light rays coming parallel to the principal axis. For this reason, it is called Concave or Diverging lens. When the light beam enters through the lens, it deviates from their path and these lenses refract the light rays. The incident rays which are parallel to the principal axis appear to diverge from a point on the principal axis after entering through the concave lens. This point is known as the focal point of a concave lens.

Question 3: Define the refraction coefficient.

Answer: Coefficient of refraction is the ratio of speed of light that travels in two different mediums. It is a dimensionless and constant quantity.

Refraction coefficient (μ) = Speed of light in first medium / Speed of light in second medium

i.e, μ = v1 / v2

Question 4: What do you mean by dispersion? Write the sequence of colours in rainbow.

Answer: The phenomenon at which white light enters through a prism and gets split into seven different colours such as violet, indigo, blue, green, yellow, orange and red. This is known as Dispersion of light. This occurs when the sun rays pass through a glass prism and forms an array of seven different colours. When we see the strips of seven colours on the wall, it is known as “Spectrum of light”.

Question 5: The two classmates of Meena are Raghav and Megha, Raghav is not able to see distant objects and Megha is not able to see near objects. What are eye’s defects they have? To remove these defects, which type of lens should they use in their spectacles?

Answer: Raghav is suffering from nearsightedness or myopia. It can be corrected by using the concave lens spectacles. Whereas, Megha is suffering from farsightedness or hypermetropia. It can be corrected by using the convex lens spectacles.

### Long Type Answer Textbook Questions

Question 6: Explain the refraction of light rays from glass slab with a pictorial diagram. Refraction from glass slab

Fix a white sheet of paper on a drawing board along with two pairs of drawing pins. On the piece of paper now keep a rectangular slab of glass in the centre. Draw the sketch of a slab with pencil and name this figure as PQRS. Remove the slab thereafter and draw a normal MON at point ‘O’ and simply make an angle of incidence i.e, AO (30°) with a protector and draw a line AB. Now insert two pins vertically on this line at point A and B.

Again put the glass slab on the same sketch PQRS and observe from the opposite side and look at the images of pins ‘A’ and ‘B’. Insert another pin at point ‘C’ as you can view the pins ‘A’ and ‘B ’in such a way that point C and images of point A and B are formed in a straight line. Take one more pin ‘D’ and put it in such a way that Point A, B, C and D appear in a straight line. Slowly remove all the pins and glass slab.

Now mark the positions of ‘C’ and ‘D’ while encircling them and draw a line between them by joining the width O’. On the surface of SR, you should draw the normal O’N’ at point O’. Now, join O with O’ and extend the line AB by joining the dotted lines. Thereafter, we can observe that light moves along the line AB in air and the light ray strikes and enters the glass surface. On point O, the light ray AB in air which is a rarer medium bends towards normal while entering to denser medium, i.e. glass.

Likewise, when the light ray travels from denser to the rarer medium {i.e. glass to air) on the surface SR at point O’ it moves away from the normal.

Hence, we can say that:

1. When a light ray enters from a rarer medium (air) to a denser medium (glass), then it bends towards the normal.

2. When a light ray enters from a denser medium (glass) to a rarer medium (air), it moves away from the normal.

Question 7: Name the optical instruments which use lens. Describe it in brief.

Answer: Given below are some of the optical instruments which use lens:

1. Correction of defects of vision through lenses: In spectacles, both types of lens are being used extensively for correction of defects in vision. For instance, those who have a blurry distant vision usually tend to suffer from nearsightedness. Such people need to use concave lenses in their spectacles. On the other hand, those people who have a problem with viewing nearby objects, are known to suffer from the farsightedness defect. Such people should use the convex lens in their spectacles.

2. Simple microscope: In shops, a clock repairman uses the convex lens to see the tiny parts of the clock. This single convex lens is known as a simple microscope. In this type of microscope, the low focal length lens is being used. THis helps in magnifying the small things into an enlarged form.

3. Compound microscope: In this type of microscope, two convex lenses are fitted in a particular metal tube. The lens is located where the object is kept and is known as an objective lens. While the lens which is closer to the eye through which the object is seen is called the eye lens or eye-piece.

4. Telescope: A telescope is used to see very distant objects which are located at a very far distance. It contains two convex lenses like a compound microscope. They are also known as objective lenses and eye-piece lenses.

Question 8: Explain in brief the working and structure of the human eye. There is a flexible convex lens in our eye located which comprises muscular tissues. Due to this lens, we can view things and an image of the object is formed at the retina. Our eyes are spherical in shape, the outermost covering of the eye is white in colour. The transparent front part cornea is called the Cornea. There is a dark coloured muscular structure located behind the cornea which is known as the Iris. There is a small hole in the iris which is known as the Pupil. Its size is being controlled by the iris and the amount of light that enters our eyes is controlled by the iris.

An inverted image is formed on the retina. Retina is a light tender transparent membrane which has various light sensitive neurons, which are connected to the brain. When these neurons send signals to the brain there is a formation of image on the retina. Thereafter, the brain converts the inverted images into an erect image and we are able to view the object. The transparent liquid between the lens and retina is referred to as the vitreous humour.

Question 1: Define light.

Answer: Light is an energy source which helps us to view objects through our eyes.

Question 2: Explain Hypermetropia. How can it be corrected?

Answer: A vision condition in which nearby objects appear blurry, but distant objects can be seen very clearly is known as hypermetropia. This eye defect is also known as farsightedness. This defect can be corrected by wearing spectacles which are made up of convex lenses.

Question 3: A convex lens is also called a converging lens. Explain why.

Answer: When the parallel rays of light enter through a convex lens, they meet or converge at a single point which is known as Converging lens. The incident rays which are parallel to the principal axis get focused at a point on the principal axis after refracting from the convex lens. This point is known as (F) or the focal point of a convex lens.

Question 4: Define lens. What are the different types of lens?

Answer: Lens is the transparent medium which is covered by the two different curved surfaces. Lens are mainly two types:

1. Convex Lens (Converging lens)

2. Concave Lens (Diverging lens)

Question 5: Explain a blind spot.

Answer: Blind spot refers to the small point where the optic nerve enters the eye that has no nerve endings within the retina. This area is insensitive to light.

Question 6: What is the cause of refraction?

Answer: The refraction of light is mainly caused due to the change in the speed of light when it moves from one medium to another with a deviation from the original path.

Question 7: What will happen when a ray of light goes from a denser medium to a rarer medium?

Answer: When a ray of light passes from a denser medium to a rarer medium, it will deviate from the normal. This is due to the fact that when a light beam travels from a denser to a rarer medium, its speed accelerates and it appears to bend away from the normal.

Question 8: What kind of image is formed when an object is placed within the focal length of a convex lens?

Answer: An erect, virtual and magnified image is formed when we place an object within the focal length of a convex lens.

Question 9: Define retina. What kind of image forms on the retina?

Answer: Retina is a light tender transparent membrane which has various light sensitive neurons, which are connected to the brain. When these neurons send signals to the brain there is a formation of image on the retina. An inverted image is formed on the retina.

Question 10: Define focal length.

Answer: Focal length (f) refers to the distance between the optical centre (O) and the focal point (F) of a lens or curved mirror.

Question 11: Give at least two uses of convex lens.

Answer: Given below are two simple uses of convex lens:

1. Convex lens are used in spectacles to correct the vision defect called farsightedness or hypermetropia.

2. Convex lens is being used as a magnifying glass which are often used by clock repairmen for repairing clocks.

Question 12: Explain the bending of pencil in water.

Answer: A pencil appears to be bent when it is immersed under water due to the refraction of light. The light rays coming from the dipped portion of pencil refracts or moves away from the normal to the surface of water due to refraction.

Question 13: Define optical centre.

Answer: Optical centre (O) of the lens is a point on the principal axis inside the lens through which a ray of light passes through without any deviation.

Question 14: Explain Myopia. How can it be corrected?

Answer: A vision condition in which distant objects appear blurry, but nearby objects can be seen very clearly is known as myopia. This eye defect is also known as nearsightedness. This defect can be corrected by wearing spectacles which are made up of concave lenses.

Question 15: What will happen when a ray of light goes from a rarer medium to a denser medium?

Answer: When a ray of light passes from a rarer medium to a denser medium, it will bend towards the normal. This is due to the fact that when a light beam travels from a rarer into a denser medium, its speed slows down and it appears to bend towards the normal.

Question 16: What is a concave lens? Why is it also called a diverging lens?

Answer: A lens which is thinner in the middle part and thicker at the edges is known as Concave lens. When the parallel rays of light pass through a concave lens to the principal axis, it deviates from its focal point and refracts the light rays. Due to this reason, it is called Concave or Diverging lens.

Question 17: Define principal axis.

Answer: The line which passes through the centres of curvature and the optical centre of the faces of a curved lens or mirror is known as the Principal Axis.

Question 18: Explain the twinkling of stars at night.

Answer: The layers of atmosphere comprise different densities as they have different refraction coefficients. The light coming from stars constantly scatters after entering through these different atmospheric layers. Due to this reason, the stars seem to twinkle at night.

Question 19: What is focal point?

Answer: The focal point of convex and concave lens are mentioned below:

1. The incident rays of light parallel to the principal axis converge at a point on the principal axis after it refracts from the convex lens. This point is known as the Focal point (F) of a convex lens.

2. The incident rays of light parallel to the principal axis appear to diverge from a point on the principal axis after entering the concave lens. This point is known as the Focal point (F) of a concave lens.

Question 20: What do you mean by refractive index? What is it used for?

Answer: The refractive index is the ratio of the velocity of light in vacuum to the speed of light in a specified medium. It is mostly applied for identifying a particular substance, checking its purity or computing its concentration.

Question 21: How is a rainbow formed?

Answer: When sunlight passes through raindrops, there is refraction and a total internal reflection of light takes place, which results in the formation of a rainbow.

Question 22: Explain with an example how an image is formed by convex lens.

Answer: Take a piece of paper and a convex lens or magnifying glass. Let the sun rays pass through the lens and focus it at a point on the sheet of paper. Hold the lens or magnifying glass till the piece of paper does not start to burn. Gradually you would notice that the convex lens converges the incident parallel to the sun rays at a certain point. This point is referred to as the focal point of the lens. We can find the approximate focal length by measuring the image distance from the optical centre. This point is known as the infinitesimal small image of the sun. A real image is obtained on screen and real images are always inverted. Hence, we can say that when the object is at infinity then the image formed by the convex lens is real, inverted and infinitesimally small at the focal point. Figure about image formation by convex lens

From the above diagram, we can explain the image formation by convex lens:

 Sl. No. Position of Object Image Position Image Size Nature of Image 1. At infinity At F Infinitesimal small and inverted Real 2. At some distance away from 2F’ Between F’ and 2F Small and inverted Real 3. At 2F’ At 2F Equal and inverted Real 4. Between F’ and 2F’ Away from 2F’ Large and inverted Real 5. At F’ At infinity Very large and inverted Real 6. Between Lens and F’ Between infinity and lens Large and erect Virtual

Question 23: Write a few lines on Dr. C.V. Raman.

Answer: Dr. C.V. Raman (Dr. Chandrasekhara Venkata Raman) was an Indian physicist who won the prestigious Nobel Prize in Physics in 1930 for his marvellous contribution and work on scattering of light. The discovery of scattering of light is popularly known as the Raman effect.

In 1954, he was awarded the ‘Bharat Ratna’ by the Government of India. In 1957, he was honoured with the Lenin Peace Prize.

Dr. Chandrasekhara Venkata Raman discovered the ‘Raman effect’ on 28th February, 1926. Every year, National Science Day is celebrated in India on this day to mark the discovery of the Raman effect in memory of Dr. C.V. Raman.

We hope that the above mentioned solutions of “RBSE Class 8 Science Chapter 14 Refraction of Light” will help students build a strong foundation of the different concepts mentioned in the chapter.