AP 7th Class Science 11th Lesson Questions and Answers Light

Access to the AP 7th Class Science Study Material 11th Lesson Light Questions and Answers are aligned with the curriculum standards.

AP 7th Class Science 11th Lesson Light Questions and Answers

AP Board Solutions Class 7 Science Chapter 11 Light

Exercises

Question 1.
Fill in the blanks:
a) An image that cannot be obtained on a screen is called …………
b) Image formed by a convex ………… is always virtual and smaller in size.
c) An image formed by a ………… mirror is always of the same size as that of the object.
d) An image which can be obtained on a screen is called a ………… image.
e) An image formed by a concave $\qquad$ cannot be obtained on a screen.
Answer:
a) virtual image
b) mirror
c) plane
d) real
e) lens

Question 2.
Mark ‘T’ if the statement is true and ‘F’ if it is false:
a) We can obtain an enlarged and erect image by a convex mirror. (T/F)
b) A concave lens always form a virtual image. (T/F)
c) We can obtain a real, enlarged and inverted image by a concave mirror. (T/F)
d) A real image cannot be obtained on a screen. (T/F)
e) A concave mirror always form a real image. (T/F)
Answer:
a) False
b) True
c) True
d) False
e) False

Question 3.
Match the items given in Column I with one or more items of Column II.

Column – I	Column – II
a) A plane mirror	i) Used as a magnifying glass.
b) A convex mirror	ii) Can form image of objects spread over a large area.
c) A convex lens	iii) Used by dentists to see en larged image of teeth.
d) A concave mirror	iv) The image is always inverted and magnified.
e) A concave lens	v) The image is erect and of the same size the object.
	vi) The image is erect and smaller in size than the object.

Answer:

Column – I	Column – II
a) A plane mirror	v) The image is erect and of the same size the object.
b) A convex mirror	ii) Can form image of objects spread over a large area.
c) A convex lens	i) Used as a magnifying glass.
d) A concave mirror	iii) Used by dentists to see en larged image of teeth.
e) A concave lens	vi) The image is erect and smaller in size than the object.

Question 4.
State the characteristics of the image formed by a plane mirror.
Answer:
The characteristics of the image formed by a plane mirror are :

• The image formed by a plane mirror is virtual and erect.
• The size of the image is same as that of the object.
• The image formed by plane mirror is laterally inverted.
• The distance of the object in front of the mirror is same as the distance of the image behind the mirror.

Question 5.
Find out the letters of English alphabet or any other language known to you in which the image formed in a plane mirror appears exactly like the letter itself. Discuss your findings.
Answer:
The letters of English alphabet which give exactly same image in the plane mirror like the letter itself are:
A, H, I, M, O, T, U, V, W, X, Y

Question 6.
What is a virtual image ? Give one situation where a virtual image is formed.
Answer:
Virtual image is the image which cannot be touched and cannot be obtained on screen. Eg : The image formed by the plane mirror is a virtual image.

Question 7.
State two differences between a convex and a concave lens.
Answer:
Differences between a convex and a concave lens are as follows:

S.No.	Concave lens	Convex lens
1)	Concave lens are thicker at the edges and thinner in the middle.	Convex lens are thicker in the  middle and thinner at the edges.
2)	Concave lens always form a virtual, erect and diminished images.	Convex lens form real, inverted image, when the object is at about 50 cm from the lens. It forms virtual, erect and enlarged image, when the object is closer to the lens.
3)	Concave lens are diverging in nature.	Convex lens are converging in nature.

Question 8.
Give one use each of a concave and a convex mirror.
Answer:
Use of convex mirror: The mirror is used in roads and large buildings to allow people to see what is around the bend.
Use of concave mirror: This mirror is used by dentists to obtain a large virtual image of the teeth.

Question 9.
Which type of mirror can form a real image ?
Answer:
A concave mirror can form a real image of the object. The nature of the image depends on the distance of the object from the concave mirror.

Question 10.
Which type of lens forms always a virtual image ?
Answer:
Concave lens always form a virtual image.

Choose the correct option in questions 11-13

Question 11.
A virtual image larger than the object can be produced by a
i) concave lens
ii) concave mirror
iii) convex mirror
iv) plane mirror
Answer:
ii) Concave mirror

Question 12.
David is observing his image in a plane mirror. The distance between the mirror and his image is 4 m. If he moves 1 m towards the mirror, then the distance between David and his image will be
1) 3 m
ii) 5 m
iii) 6 m
iv) 8 m
Answer:
iii) 6 m
Note : If David moves 1 m towards the mirror then distance between his image and mirror = 4 – 1= 3 m.
So, distance between David and mirror = 3 m
Hence, distance between David and his image = 3 + 3 = 6 m.

Question 13.
The rear view mirror of a car is a plane mirror. A driver is reversing his car at a speed of 2 m/s. The driver sees in his rear view mirror the image of a truck parked behind his car. The speed at which the image of the truck appears to approach the driver will be:
i) 1 m/s
ii) 2 m/s
iii) 4 m/s
iv) 8 m/s
Answer:
iii) 4 m/s
Note : The speed of the bike is 2 m/s, which means the bike is reaching the truck at a speed of 2 metres per second. The separation between the bike and truck will be reduced at a double rate. The reason behind this is the image of the truck appearing to approach the driver with the speed of 2 x 2 = 4 m/s.

Questions given in the lesson

Page No. 88

Question 1.
Paheli wants to know, what makes things visible to us? Boojho thinks that objects are visible only when light reflected from them reaches our eyes. Do you agree with him?
Answer:
Things are visible to us because of the reflection of light.

Page No. 90

Question 2.
Boojho noted in his notebook: Is it not surprising that my image is of the same size as me whether the mirror is small or large ?
Answer:
Yes, image formed by the plane mirror is of the same size as the object. A plane mirror has plane reflecting surface without any curve.

Question 3.
Paheli made note in her notebook: In a plane mirror the image is formed behind the mirror. It is erect, of the same size and is at the same distance from the mirror as the object is in front of it .
Answer:
Yes, the plane mirror always forms an image of the same size and erected image.

Page No. 92

Question 4.
Boojho saw an ambulance on the road. He was surprised to see that the word ‘AMBULANCE’ in front was written in a strange manner
Answer:
The image found on rear view mirror of the vehicle is laterally inverted i.e., right appears left and left appears right. So, when the driver of vehicle ahead of an ambulance looks in his/her rear view mirror, he/she can read the strange word as written on it.

Page No. 96

Question 5.
Why are concave and convex mirrors called spherical mirrors ?
Answer:
Concave and convex mirrors are called spherical mirrors because the reflecting surfaces, of concave and convex mirrors are considered to form a part of a hollow sphere.Their reflecting surface is not a plane surface.

Page No. 108

Question 6.
Does this mean that the white light consists of seven colours?
Answer:
Yes, white light consists of seven colours – red, orange, yellow, green, blue, indigo and violet. Prism splits a beam of sunlight into seven colours.

Question 7.
Paheli wants to tell you that you can see a rainbow only when your back is towards the sun.
Answer:
Yes, the sun always has to be behind you, though, because the light gets refracted back in the general direction it came from. You’ll never see a rainbow when you’re facing the sun. From wherever you’re standing, it looks like the rainbow actually exists in some physical form.

Extended Learning – Activities and Projects

Question 1.
Play with a mirror.
Write your name with a sketch pen on a thin sheet of paper, polythene or glass. Read your name on the sheet while standing in front of a plane mirror. Now look at your image in the mirror.
Answer:
Hint: The letters get laterally inverted.

Question 2.
A burning candle in water.
Take a shoe box, open on one side. Place a small lighted candle in it. Place a clear glass sheet (roughly 25 cm x 25 cm) in front of this candle (Figure).Try to locate the image of the candle behind the glass sheet. Place a glass of water at its position. Ask your friends to look at the image of the candle through the sheet of glass. Ensure that candle is not visible to your friends. Your friends will be surprised to see the candle burning in water. Try to explain the reason. Candle burning in water.

Answer:
When we put a glass filled with water in that position, then the image of the burning candle appears in it. This is all because plane glass sheet is a transparent. So the image of burning candle is formed behind the glass sheet.

Question 3.
Make a rainbow :
Try to make your own rainbow. You can try this project in the morning or in the evening. Stand with your back towards the Sun. Take a hosepipe or a water pipe used in the garden. Make a fine spray in front of you. You can see different colours of rainbow in the spray.
Answer:
Student activity

Question 4.
Visit a laughing gallery in some science centre or a science park or a village mela. You will find some large mirrors there. You can see your distorted and funny images in these mirrors. Try to find out the kind of mirrors used there.
Answer:
Spherical mirrors are used to form funny images. This is because normal plane mirrors produce a perfect image whereas we need distorted, funny images which can be only produced by curved mirrors.

Question 5.
Visit a nearby hospital. You can also visit the clinic of an ENT specialist, or a dentist. Request the doctor to show you the mirrors used for examining ear, nose, throat and teeth. Can you recognise the kind of mirror used in these instruments?
Answer:
Concave mirrors are used by the dentists because at a short range, the concave mirrors, produce a magnified, upright images of face. By these is mirrors, dentist can examine the patients more easily.

Question 6.
Role play:
Here is a game that a group of children can play. One child will be chosen to act as object and another will act as the image of the object. The object and the image will sit opposite to each other. The object will make movements, such as raising a hand, touching an ear etc. The image will have to make the correct movement following the movement of the object. The rest of the group will watch the movements of the image. If the image fails to make the correct movement, she/he will be retired. Another child will take her/his place and the game will continue. A scoring scheme can be introduced. The group that scores the maximum will be declared the winner.
Answer:
Student Activity.

Activities 

Activity 11.1 Page No: 86

Question 1.
Take a torch. Cover its glass with a chart paper which has three narrow slits as shown in Figure. Spread a sheet of chart paper on a smooth wooden board. Fix a plane mirror strip vertically on the chart paper. Now direct the beam of light on the mirror from the torch with slits. Place the torch in such a way that its light is seen along the chart paper on the board. Now adjust its position so that the light from the torch strikes the plane mirror at an angle (Figure).
Does the mirror change the direction of light that falls on it? Now move the torch slightly to either side. Do you find any change in the direction of reflected light?
Answer:
Aim : To show the reflection of light from a mirror.
Materials required : Torch, chart paper, smooth wooden board, plane mirror.

Procedure:

• Take a torch.
• Cover its glass with a chart paper which has three narrow slits as shown in Figure.
• Spread a sheet of chart paper on a smooth wooden board.
• Fix a plane mirror strip vertically on the chart paper (Figure).
• Now direct the beam of light on the mirror from the torch with slits.
• Place the torch in such a way that its light is seen along the chart paper on the board.
• Now adjust its position so that the light from the torch strikes the plane mirror at an angle (Figure).

Observations: We observe that the mirror reflects back the light striking it. When we slightly move the torch to either side. It is noticed that the direction of the reflected light changes with respect to the incident light, and the angle of incidence always remains equal to the angle of reflection.

Conclusion : From the above activity, we can conclude that light get reflected by a plane mirror.

Activity 11.2 Page No: 88

Question 2.
Place a lighted candle in front of a plane mirror. Try to see the flame of the candle in the mirror. It appears as if a similar candle is placed behind the mirror. The candle, which appears behind the mirror, is the image of the candle formed by the mirror.The candle itself is the object. Now move the candle to different positions in front of the mirror.

Observe the image in each case. Was the image upright in each case ? Did the flame appear on top of the candle as in the object? Now place a vertical screen behind the mirror. Try to obtain the image of the candle on this screen. Can you get the image on the screen? Now place the screen in front of the mirror. Can you get the image on the screen now?
Answer:
Aim : To show that the image formed in a plane mirror is erect and virtual.
Materials required : Candle and a large sized plane mirror.

Procedure:

• Place a lighted candle in front of a plane mirror.
• Try to see the flame of the candle in the mirror.
• It appears as if a similar candle is placed behind the mirror.
• The candle, which appears behind the mirror, is the image of the candle formed by the mirror. The candle itself is the object.
• Now move the candle to different positions in front of the mirror. Observe the image in each case.
• Now place a vertical screen behind the mirror.
• Try to obtain the image of the candle on this screen.
• Now place the screen in front of the mirror.

Observation : We observe when we place a vertical screen behind the mirror the image of candle cannot be obtained on the screen. We also noticed when we place the screen in front of the mirror the image of candle cannot be obtained on the screen in this case also.

Conclusion : From the above activity we can conclude that the image formed in a plane mirror is erect and virtual.

Activity 11.3 Page No: 90

Question 3.
Take a chess board. If a chess board is not available, draw on a chart paper 64(8×8) squares of equal size. Draw a thick line in the middle of the paper. Fix a plane mirror
Locating image in a plane mirror
vertically on this line. Place any small object, such as a pencil sharpner, at the boundary of the third square counting from the mirror (Figure). Note the position of the image. Now shift the object to the boundary of the fourth square. Again note the position of the image. Did you find any relation between the distance of the image from the mirror and that of the object in front of it?
Answer:
Aim : To locating image in a plane mirror.
Materials required : Chess board, mirror.

Procedure:

• Take a chess board.
• If a chess board is not available, draw on a chart paper 64(8×8) squares of equal size.
• Draw a thick line in the middle of the paper. Fix a plane mirror vertically on this line.
• Place any small object, such as a pencil sharpner, at the boundary of the third square counting from the mirror.
• Note the position of the image.
• Now shift the object to the boundary of the fourth square.
• Again note the position of the image.

Observation : We observe that the image is formed at the same distance behind the mirror as the object is in front of it.

Conclusion : From the activity we can conclude that image is at same distance behind mirror as object is in front of it.

Activity 11.4 Page No: 92

Question 4.
Stand in front of a plane mirror and look at your image. Raise your left hand. Which hand does your image raise (Figure) ? Now touch your right ear. Which ear does your hand touch in your image? Observe carefully. You will find that in the mirror the ‘right’ appears ‘left’ and the ‘left’ appears ‘right’. Note that only sides are interchanged; the image does not appear upside down. Now write; down your name on a piece of paper and hold it in front of a plane mirror. How does it appear in the mirror?
Answer:
Aim: To show that the images are formed in a plane mirror is laterally inverted.
Materials required : A large size mirror.

Procedure:

• Stand in front of a plane mirror and look at your image.
• Raise your left hand.
• Now touch your right ear.
• Observe carefully.
• Now write down your name on a piece of paper and hold it in front of a plane mirror.

Observations: When we lift our left hand the images appear to lift its right hand. When we touch your left ear with your right hand in front of a plane mirror it will be seen in the mirror that your right ear is touched with your left hand. When we write down your name on a piece of paper and hold it in front of a plane mirror. It will appear totally opposite in the mirror.

Conclusion : When an object is placed in front of a plane mirror, the lateral sides of the object are changed and this is called lateral inversion.

Activity 11.5 Page No : 94

Question 5.
Take a stainless steel spoon. Bring the outer side of the spoon near your face and look into it. Do you see your image in it (Figure) ? Is this image different from what you see in a plane mirror? Is this image erect? Is the size of the image the same, smaller or larger? Now look at your image using the inner side of the spoon.
Answer:
Aim : To show the image from the outer side of a spoon.
Materials required : Stainless steel spoon.

Procedure:

• Take a stainless steel spoon.
• Bring the outer side of the spoon near your face and look into it.

Observations: We observe when we see our face from the outer surface of the spoon .We will see a virtual, erect and a smaller image.When we observe our face on the inner side of the spoon we see the upright image of ourself and the image is erect and larger in size.

Conclusion : From the above activity we can conclude that the outer surface of the spoon acts as a convex mirror, and inner surface of a mirror acts like a concave mirror.

Activity 11.6 Page No : 86

Question 6.
Take a concave mirror. Hold it facing the Sun. Try to get the light reflected by the mirror on a sheet of paper. Adjust the distance of the paper until you get a sharp bright spot on it (Figure). Hold the mirror and the sheet of paper steady for a few minutes. Does the paper start burning?
Answer:
Aim To sow that a concave mirror forms a real image of the sun.
Materials required : A concave mirror and a sheet of paper.

Procedure :

• Take a concave mirror.
• Hold it facing the Sun.
• Try to get the light reflected by the mirror on a sheet of paper.
• Adjust the distance of the paper until you get a sharp bright spot on it.
• Hold the mirror and the sheet of paper steady for a few minutes.

Observation : We observe while doing this activity, the paper starts burning because the real image of sun is formed by the concave mirror.

Conclusion : From the above activity, we can conclude that concave mirror forms a real images.

Activity 11.7 Page No : 96

Question 7.
Fix a concave mirror on a stand (any arrangement to keep the mirror steady would do) and place it on a table (Figure a). Paste a piece of white paper on a cardboard sheet (say about 15 cm x 10 cm). This will act as a screen. Keep a lighted candle on the table at a distance of about 50 cm from the mirror. Try to obtain the image of the flame on the screen.

For this, move the screen till a sharp image of the flame is obtained. Make sure that, the screen does not obstruct the light from the candle falling on the mirror. Is this image real or virtual? Is it of the same size as the flame? Now move the candle towards the mirror and place it at different-distances from it. In each case try to obtain the image on the screen. Record your observation in Table. Is it possible to obtain the image on the screen when the candle is too close to the mirror (figure b).

Image formed by a concave mirror for object placed at different distances from it.

Distance of the object from the mirror	Smaller/larger than the object	Character of the image
		Inverted/ erect	Real/virtual
50 cm
40 cm
30 cm
20 cm
10 cm
5 cm

Answer:
Aim : To study the real and virtual images formed by a concave mirror.
Materials required : Concave mirror, stand, table, piece of white paper, cardboard, candle.

Procedure :

• Fix a concave mirror on a stand (any arrangement to keep the mirror steady would do) and place it on a table.
• Paste a piece of white paper on a cardboard sheet.
• Keep a lighted candle on the table at a distance of about 50 cm from the mirror.
• Try to obtain the image of the flame on the screen.
• For this, move the screen till a sharp image of the flame is obtained.
• Make sure that, the screen does not obstruct the light from the candle falling on the mirror.

Observations : We observe that the image is virtual and is of the same size of the object. We observe it is not possible to obtain the image on the screen when the candle is too closed to the concave mirror.

Image formed by a concave mirror for object placed at different distances from it.

Distance of the object from the mirror	Smaller/larger than the object	Character of the image
		Inverted/ erect	Real/virtual
50 cm	Larger	Inverted	Real
40 cm	Larger	Inverted	Real
30 cm	Highly enlarged	Inverted	Real
20 cm	Enlarged	Erect	Virtual
10 cm	Enlarged	Erect	Virtual
5 cm	Enlarged	Erect	Virtual

Conclusion: From the above activity, we can conclude that the image formed by concave mirror can be smaller or larger in size than object. Image may be real or virtual.

Activity 11.8 Page No: 100

Question 8.
Repeat Activity 11.7 now with a convex mirror in place of a concave mirror (Figure). Record your observations in a Table similar to Table 11.1. Could you get a real image at any distance of the object from the convex mirror? Did you get an image larger in size than the object?
Answer:
Aim : To study the images formed by a convex mirror.
Materials required : Convex mirror, mirror stand, candle and white paper screen.

Procedure :

• Mount a convex mirror on a mirror stand and place it on the table.
• Place a screen made from white paper at a distance in front of it.
• Place a lighted candle in between the mirror and the screen.
• Move the screen to see if any images are formed on it.
• No image is seen on the screen.
• Now look into the convex mirror. An erect and smaller image is seen in the mirror.
• Slowly move the candle away from the mirror and keep observing the nature of the image formed in the mirror.

Observation : We observe in a convex mirror the images of the candle are smaller and erect at all distances.

Conclusion : From the above activity, we can conclude that the convex mirrors always form erect and small sized images.

Activity 11.9 Page No : 104

Question 9.
Take a convex lens or magnifying glass.
Put it in the path of sunrays. Place a sheet of paper as shown (Figure). Adjust the distance between the lens and the paper till you get a bright spot on the paper. Hold the lens and the paper in this position for a few minutes. Does the paper begin to burn? Now replace the convex lens with a concave lens. Do you see a bright spot on the paper this time, too ? Why are you not getting a bright spot this time?
Answer:
Aim : To study the real image of the sun by a convex lens.
Materials required : Convex lens, sheet of paper.

Procedure:

• Take a convex lens or magnifying glass.
• Put it in the path of sun rays.
• Place a sheet of paper as shown in the above figure.
• Adjust the distance between the lens and the paper till you get a bright spot on the paper.
• Hold the lens and the paper in this position for a few minutes.
• Observe carefully.
• Now replace the convex lens with a concave lens.
• Record your observations.

Observations: We observe paper begins to burn due to the converging light rays of the sun. When we replace convex lens with concave lens no bright spot is observed because sun rays are diverged after reflection.

Conclusion: From the above activity, we can conclude that the convex lens is thinner at the edges and thicker in the centre. It is a converging lens converges light rays. and form real, inverted, and diminished image.

Activity 11.10 Page No: 104

Question 10.
Take a convex lens and fix it on a stand as you did with the concave mirror. Place it on a table. Place a lighted candle at a distance of about 50 cm from the lens. Try to obtain the image of the candle on a paper screen placed on the other side of the lens. You may have to move the screen towards or away from the lens to get a sharp image of the flame. What kind of image did you get ? Is it real or virtual?
Answer:
Aim : To study the image by a convex lens for object placed at different distances from it. Materials required : Convex lens, stand, a lighted candle, paper screen.

Procedure:

• Take a convex lens and fix it on a stand as you did with the concave mirror.
• Place it on a table.
• Place a lighted candle at a distance of about 50 cm from the lens [Figure (a)]
• Try to obtain the image of the candle on a paper screen placed on the other side of the lens.
• You may have to move the screen towards or away from the lens to get a sharp image of the flame.

Observation : We obtain a sharp image of candle on paper screen placed on other side of lens. The obtained image is real.

Conclusion : From the above activity we can conclude that the convex lens converges (bends inward) light falling on it.

Activity 11.11 Page No: 108

Question 11.
Take a glass prism. Allow a narrow beam of sunlight through a small hole in the window of a dark room to fall on one face of the prism. Let the light coming out of the other face of the prism fall on a white sheet of paper or on a white wall. What do you observe? Do you see colours similar to those in a rainbow.
Answer:
Aim : To show that sunlight consists of seven colours.
Materials required : Glass prism and a white sheet of paper.

Procedure:

• Take a glass prism.
• Allow a narrow beam of sunlight through a small hole in the window of a dark room to fall on one face of the prism.
• Let the light coming out of the other face of the prism fall on a white sheet of paper or on a white wall.

Observation : We observe when the light coming out of the other face of the prism falls on a white sheet then a band of seven colours appear on the screen.

Conclusion : From the above activity, we can conclude that when a beam of white light is passed through a glass prism, tenth white light splits to form a band of seven colours on white screen. Hence, sunlight is made up of seven colours.

Activity 11.12 Page No: 110

Question 12.
Take a circular cardboard disc of about 10 cm diameter. Divide this disc into seven segments. Paint the seven rainbow colours on these segments as shown in Figure (a). You can also paste, coloured papers on these segments. Make a small hole at the centre of the disc. Fix the disc loosely on the tip of a refill of a ball pen. Ensure that the disc rotates freely [Figure (a)]. Rotate the disc in the daylight.
Answer:
Aim : To show that white light consists of seven colours.
Material required : Circular cardboard disc, paint.

Procedure:

• Take a circular cardboard disc of about 10 cm diameter.
• Divide this disc into seven segments.
• Paint the seven rainbow colours on these segments as shown in Figure (a).
• You can also paste, coloured papers on these segments.
• Make a small hole at the centre of the disc.
• Fix the disc loosely on the tip of a refill of a ball pen.
• Ensure that the disc rotates freely [Figure (a)].
• Rotate the disc in the daylight.

Observations: When the disc is rotated fast, the colours get mixed together and the disc appears to be whitish. Such disc is known as Newton’s disc.

Conclusion : From the above activity, we can conclude that white light consists of seven colours i.e., Violet, Indigo, Blue, Green, Yellow, Orange and Red (VIBYOR).