Question 1.
Suppose you are in a dark room. Can you see objects in the room? Can you see objects out¬side the room? Explain.
When we are in a dark room then we cannot see objects in the room. We can see the objects outside the room, because out of the room the light is available and the rays of light can enter our eyes after reflection from the objects.
Question 2.
Differentiate between regular and diffused reflection. Does diffused reflection mean the failure of the laws of reflection?
| Regular Reflection | Diffused Reflection |
| (i) All the reflected rays are parallel. | (i) The reflected rays are not parallel. |
| (ii) It occurs on a smooth and polished surface. | (ii) It occurs on the rough surface. |
| (iii) Reflected rays are in one direction. | (iii) Reflected rays are scattered in different directions. |
No, diffuse reflection doesn’t mean the failure of laws of reflection.
Question 3.
Mention against each of the following whether regular or diffused reflection will take place when a beam of light strikes. Justify your answer in each case.
- Polished wooden table
- Chalk powder
- Cardboard surface
- Marble floor with water spread over it
- Mirror
- Piece of paper
- Regular reflection will take place because the surface is plane and polished.
- Diffused reflection will take place because the surface is rough.
- Diffused reflection will take place because the surface is rough.
- Regular reflection will take place because the surface is smooth and plane.
- Regular reflection will take place because the surface is plane and polished.
- Diffused reflection will take place because the surface is rough.
Question 4.
State the laws of reflection.
The laws of reflections are:
- The incident ray, the normal and the reflected ray, all lie in the same plane.
- The angle of incidence is equal to the angle of reflection.
Question 5.
Describe an activity to show that the incident ray, the reflected ray and the normal at the point of incidence lie in the same plane.
Activity: To show that the incident ray, reflected ray and the normal at the point of incidence lie in the same plane.
Materials Required: Plane mirror, holder, ray box, etc.
Procedure: Fix sheet of white paper, a little beyond the edge of the board. Place a plane mirror strip vertically to the paper using a stand. Throw light from a ray box on the mirror. Look at the reflected ray. Mark the incident ray, normal ray and reflected ray. Fold the paper which is beyond the edge of the board. You will observe that the reflected ray is not seen in the folded portion of the chart paper. Now bring the folded portion back to its original position. The reflected ray of light is again seen on the page.
Conclusion: The sheet on the board can be considered as a plane. The incident ray, the reflected ray, the normal at the point of incidence lie in the same plane.
Incident ray, reflected ray and normal at the point of incidence lie in the same plane
Question 6.
Fill in the blanks in the following.
(a) A person 1 m in front of a plane mirror seems to be ______ m away from his image.
(b) If you touch your ______ ear with a right hand in front of a plane mirror it will be seen in the mirror that your right ear is touched with _____
(c) The size of the pupil becomes _______ when you see in dim light.
(d) Night birds have _______ cones than rods in their eyes.
(a) 2
(b) left, left hand
(c) larger
(d) lesser
Question 7.
The angle of incidence is equal to the angle of reflection
(a) Always
(b) Sometimes
(c) Under special conditions
(d) Never
(a) Always
Question 8.
The image formed by a plane mirror is:
(a) virtual, behind the mirror and enlarged.
(b) virtual, behind the mirror and of the same size as the object.
(c) real at the surface of the mirror and enlarged.
(d) real, behind the mirror and of the same size as the object.
(b) virtual, behind the mirror and of the same size as the object.
Question 9.
Describe the construction of a kaleidoscope.
Kaleidoscope is a device based on the principle of multiple reflections. It consists of three long and narrow strips of plane mirrors inclined at an angle of 60° to one another forming prism. This is fitted in a tube. One end of this tube is closed by a cardboard disc having a hole at its centre. To the other end touching the mirrors plane glass plate is fixed on which broken pieces of coloured bangles are placed. This end of the tube is closed by a ground glass plate.
Question 10.
Draw a labelled sketch of the human eye.
Question 11.
Gurmit wanted to perform Activity 16.8 using a laser torch. Her teacher advised her not to do so. Can you explain the basis of the teacher’s advise?
Teacher has advised Gurmit not to do so because laser light is very harmful for her eyes and can cause a permanent defect in the eye. Person can even lose his or her eyesight if laser torch is directed over the eyes.
Question 12.
Explain how you can take care of your eyes.
Eyes are very precious. We must take proper care of them. We must
- always sit straight while reading or writing.
- if advised, use suitable spectacles.
- wash our eyes with clean water frequently.
- not look at the sun directly.
- always read or write in a proper light.
Question 13.
What is the angle of incidence of a ray if the reflected ray is at an angle of 90° to the incident ray?
Here, the angle of reflection is 90°. As we know, according to the laws of reflection that angle of incidence is equal to angle of reflection.
Here, the angle between the incident ray and reflected ray is 90°.
i.e., ∠i + ∠r = 90°
Since, ∠i = ∠r
We can write, ∠i + ∠i = 90°
⇒ 2∠i = 90°
⇒ ∠i = 45°
Angle of incidence = 45°.
Question 14.
How many images of a candle will be formed if it is placed between two parallel plane mir¬rors separated by 40 cm?
Here, mirrors are placed parallel to each other 40 cm apart. Therefore, an infinite number of images will be formed.
Question 15.
Two mirrors meet at right angles. A ray of light is incident on one at an angle of 30° as shown in Fig. 16.19. Draw the reflected ray from the second mirror.
Question 16.
Boojho stands at A just on the side of a plane mirror as shown in Fig. 16.21. Can he see himself in the mirror? Also, can he see the image of objects situated at P, Q, and R?
No, Boojho can’t see himself in the mirror. He can see the image of the object at P and Q but not of R.
Question 17.
(a) Find out the position of the image of an object situated at A in the plane mirror (Fig. 16.23).
(b) Can Paheli at B see this image?
(c) Can Boojho at C see this image?
(d) When Paheli moves from B to C, where does the image of A move?
(a) It is shown in the following figure.
(b) Yes, Paheli can see the image of A.
(c) Yes, Boojho can see the image of A.
(d) Image of the object at A will not move as an object is not moving.
Question 18.
Define dispersion of light.
Splitting up of white light into seven colours when it passes through a glass prism is known as dispersion of light.
Question 19
Name the colours in the order they appear in the spectrum of light.
VIBGYOR – Violet, Indigo, Blue, Green, Yellow, Orange and Red.
Question 20.
Angle of incidence is equal to the angle of reflection.
- Always
- Sometimes
- Under special conditions
- Never
Always.
Question 21.
Image formed by a plane mirror is [NCERT]
- virtual, behind the mirror and enlarged.
- virtual, behind the mirror and of the same size as the object.
- real at the surface of the mirror and enlarged.
- real, behind the mirror and of the same size as the object.
virtual, behind the mirror and of the same size as the object.
Question 22.
What is the angle of incidence of a ray if the reflected ray is at an angle of 90° to the incident ray ?
The angle of incidence = 45°.
Question 23.
What are the two factors responsible for an object to be seen ?
To be seen an object, the sense of vision and light are required.
Question 24.
What is meant by normal ?
The perpendicular drawn at the point of incidence is known as normal.
Question 25.
Define the angle of incidence.
The angle between the incident ray and the normal is known as angle of incidence.
Question 26.
What name is given to the angle between the normal and the reflected ray ?
Angle of reflection.
Question 27.
What is meant by lateral inversion?
Lateral inversion is the phenomenon of the interchange of the left and right sides, between the object and its image.
Question 28.
When the reflected rays are parallel, what type of reflection is taking place ?
Regular reflection.
Question 29.
In irregular reflection, are the reflected rays parallel or not ?
In irregular reflection the reflected rays are not parallel.
Question 30.
What are illuminated objects ?
Objects which reflect the light falling on them and can be seen are known as illuminated objects
Question 31.
What is white light ?
Sunlight is a mixture of seven colours also known as white light.
Question 32.
Give one example of natural dispersion.
Formation of rainbow.
Question 33.
What is function of iris ?
Iris controls the amount of light entering into the eyes.
Question 34.
What is meant by visually challenged people ?
Visually challenged people have limited vision to see things.
Question 35.
What are non-optical aids ?
Non-optical aids include visual aids, tactual aids, auditory aids and electronic aids
Question 36.
What are tactual aids ?
Tactual aids include Braille writer, slate and stylus. They help the visually challenged persons in taking notes, reading and writing and in learning mathematics.
Question 37.
Fill in the blanks :
- The angle of reflection is ………… to the angle of incidence.
- The image formed by a plane mirror is ………….. inverted with respect to the object.
- The …………….. uses two plane mirror strips each of which is kept inclined at 45° to the axis of the tube.
- equal
- laterally
- periscope.
Question 38.
Write one/two-word answer for each of the following :
- The ray of light that bounces back from a plane mirror.
- The nature of the image formed by a plane mirror.
- The number of images formed by a pair of parallel plane mirrors.
- A devices that is often used as “looking glass”.
- Reflected ray
- Virtual image
- Multiple images
- Mirror.
Question 39.
Which kind of spherical mirrors are used in vehicles? Why?
A convex mirror is used in vehicles because it gives the driver a large field of view.
Question 40.
Why is it important to take care of our eyes? Mention any two activities that may cause damage to our eyes.
Eyes are the most wonderful gift of nature to us and they must serve us for our whole life. Our eyes can be damaged by playing carelessly or by hurting them with sharp projections
Question 41.
Suppose you are in a dark room. Can you see object in the room ? Can you see objects outside the room ? Explain.
The objects cannot be seen inside the room because there is no light. The objects outside the room can only be seen if there is light outide.
Question 42.
State the laws of reflection.
Laws of reflection:
- The incident ray, the reflected ray and the normal at the point of incidence lie in the same plane.
- The angle of incidence is equal to the angle of reflection
Question 43.
Distinguish between real and virtual image.
Differences:
| Real image | Virtual image |
| (a)The rays actually meet at a point. (b) The image can be obtained on a screen. |
(a)The rays donot meet at a point. (b)The image cannot bje obtained on a screen. |
Question 44.
What is the function of the eyelids ?
- Eyelids prevents the objects from entering the eye.
- They also shut out light when not required.
Question 45.
Give some uses of plane mirror.
Plane mirrors are used for dressing up, shaving beards, in scientific metres and for designing periscope.