Reviewing SCERT Kerala Syllabus 7th Standard Basic Science Notes Pdf and Class 7 Basic Science Chapter 4 Question Answer Notes Solutions Pdf When Light Reflects can uncover gaps in understanding.
When Light Reflects Class 7 Questions and Answers Notes
Class 7 Basic Science Chapter 4 When Light Reflects Question Answer Pdf
Basic Science Class 7 Chapter 4 Question Answer Kerala Syllabus
Let Us Assess
Question 1.
Examine the following table and find the odd one out.
Answer:
Transparent objects – Box filled with smoke
Translucent objects – Tiles
Opaque objects – Clear water, Fog
Question 2.
Observe the pictures. Which type of reflections do you see here?
Answer:
Picture 1 – Regular reflection
Picture 2 – Diffused reflection
Question 3.
Observe the following situations. Find out which type of reflection takes place in each.
Answer:
| Situation | Reflection |
| Ornaments shine | Diffused reflection |
| We get light inside the home during day time | Diffused reflection |
| A polished furniture shines | Regular reflection |
| See reflection of trees on stagnant water | Regular reflection |
Class 7 Basic Science Chapter 4 Extended Activities Answers
Question 1.
Arrange three benches in a room as shown in the figure given below. Arrange one of them perpendicular to the wall and keep the others at a particular distance from the wall. Fix a nail on the bench at the end which touches the wall. Place a mirror vertically behind the nail fixed on the bench. Mark A, B at equal intervals at one of the benches placed away from the wall.. Similarly mark C, D on the other bench. At the end of the bench perpendicular to the wall, mark X as shown in the figure. Make four children sit on the bench at position A, B, C and D. Wrap a thread around the nail and give the two ends of it to the children in positions A and D. Similarly, wrap another thread around the nail and give the ends to the children in positions B and C.
a. Light a torch on to the mirror through the thread held bv child A. Where does the reflected light fall?
Answer:
The reflected light falls on child D.
b. Similarly, let child D also light the torch on the mirror. Where does the reflected light fall?
Answer:
The reflected light falls on child A.
c. Let the children B and C repeat the activity. Write down your observations.
Answer:
When the torch is lit through the thread held by child B, the reflected light falls on child C. Similarly, when the torch is lit through the thread held by child C, the reflected light falls on child B.
d. Where will the reflected light fall, if the torch is lighted on to the mirror from X?
Answer:
The reflected light will fall on X.
Class 7 Basic Science Chapter 4 Intext Question and Answers
Question 1.
Why did grandma ask the girl to close the curtain when light entered the room through the window?
Answer:
The curtain does not allow the light to enter into the room.
Question 2.
What are the things that can be used instead of a curtain to prevent sunlight from entering a room through a glass window? List them.
Answer:
- use wooden screens
- use rubber screens
- use plastic curtains
- paint it black
- use suitable papers to cover glass
Experiment – to find substances that transmit light and substances that do not transmit light Point a lighted torch at different objects such as scratched glass sheet, glass filled with pure water, wooden block, a piece of cloth, white paper, black chart paper, butter paper, window glass, a coin, a mirror, a piece of reading glass, marble, polythene cover and a colourless plastic bottle.
Question 3.
What do you observe?
Answer:
Question 4.
Didn’t light pass through the butter paper? What about the glass used in spectacles? Do both of these substances transmit light in the same manner? Record it.
Answer:
Yes, some amount of light passed through the butter paper.
Light also passes through the glass used in spectacles.
No, both these substances do not transmit light in the same manner. Butter paper transmits light partially, whereas glass used in spectacles transmits light completely.
Repeat the experiment using butter paper, window glass, scratched glass piece, oiled paper, glass piece, polythene cover,’pure water taken in a glass tumbler and colourless plastic bottle.
Question 5.
On the basis of the experiment, classify them as those which transmit light completely and those which transmit light partially.
Answer:
Question 6.
Repeat the experiment using more objects. Classify them as transparent, translucent and opaque objects and record them in the Science Diary.
Answer:
Question 7.
Can you change a transparent glass sheet into a translucent or opaque one? How? Discuss. What methods can you suggest? Record them in the Science Diary.
Answer:
Yes, we can.
To make it transparent – cover it with opaque objects, paint or soot.
To make it translucent – add oil, soot lightly or paint lightly.
Make a transparent glass sheet sooted, as shown in the figure below.
Question 8.
What change do you observe?
Answer:
A sheet of transparent glass turns less clear when it accumulates soot on it. Depending on how thick the soot deposit is, glass can go from transparent to translucent or even opaque.
Question 9.
What happens to the light transmitting property of transparent glass sheet when it becomes sootier? Do an experiment to find it out.
Answer:
The below given is an experiment to find out what happens to the light transmitting properties of transparent glass sheet when it becomes sootier:
Materials Required:
- A transparent sheet of glass
- A candle or a soot producing material
- Source of light (flashlight or torch)
Procedure:
- Measure the initial amount of light going through the clean, transparent glass sheet by passing light through it.
- To apply a tiny layer of soot to one side of the glass sheet, hold it over a candle flame or a burning piece of paper. Make sure everything is covered equally.
- Now, pass the light through the sooted glass sheet.
- Compare the light intensity before and after sooting the glass sheet.
Observation:
After applying the soot, a noticeable decrease in the amount of light that is travelling through the glass sheet can be observed.
Question 10.
What other methods can be adopted to make the glass sheet translucent or opaque? Write down your suggestions in the Science Diary.
Answer:
Methods to make glass translucent
1) Frosted Film Application: Glass can be made translucent by applying a frosted plastic film to it.
2) Using Frosted Spray Paint: To give glass a translucent appearance, mist it with frosted glass paint.
Methods to make glass opaque
1) Painting: Light will be blocked if an opaque paint or coating is applied to the glass’s surface.
2) Covering with Opaque Material: We can make the glass opaque by sticking opaque plastic or vinyl sheets to it.
Question 11.
You have found that pure water is transparent. What about air?
Answer:
Visible light can usually pass through pure air. However, air can have dust, water droplets, or pollutants in it that can scatter light and make it look less transparent (for example, when it’s foggy or smoggy).
Question 12.
Can we convert pure water and air to translucent? Design an experiment for this.
Answer:
Yes, we can convert pure water and air to translucent.
To convert pure water to translucent
Fill 3/4 of a plastic bottle with water. Point light from a torch to it. Light passes through water. Add a few drops of blue ink to the water. Repeat the experiment. Now light will transmit through it partially.
To convert air to translucent
Take a transparent glass bottle. Point a lighted torch to it and observe. Light will transmit through it. Now, fill some smoke in the bottle using burning incense sticks. Again, repeat the experiment. Now the light will transmit through it partially.
Question 13.
What other substances can you use for this? Design an experiment using the materials you have identified. Record the details and findings of the experiment in your Science Diary.
Answer:
To make water translucent ujala, liquid blue, ink, etc can be used. The presence of dust particles and mist in air make air translucent. Experiment to make water translucent: Fill a plastic bottle with water. Point light from a torch to it. Light passes through water. Add a few drops ujala or liquid blue or ink to the water. Repeat the experiment. Now light will transmit through it partially.
Experiment to make air translucent: Take a transparent glass bottle. Point a lighted torch to it and observe. Light will transmit through it. Now, fill some dust particles or mist in the bottle. Again, repeat the experiment. Now the light will transmit through it partially.
Question 14.
Haven’t you understood that some transparent substances can be converted to opaque substances?
Answer:
Yes
Question 15.
How does the opacity and transparency of objects benefit us?
Answer:
The opacity and transparency of objects benefit us by allowing us to control light and visibility. For ..example, transparent windows let light in, while opaque walls provide privacy.
Question 16.
How do you know when the ink in a refill pen is completely used up?
Answer:
The ink in a refill pen is completely used up when the pen no longer writes, and you can often see that the refill pen is empty if the pen has a transparent or translucent casing.
Question 17.
Don’t you use oil paper to trace pictures and maps?
Answer:
Yes, oil paper (tracing paper) is commonly used to trace pictures and maps because its translucency helps you to see the image beneath clearly.
Question 18.
Haven’t you realised that we utilise the transparency, opacity and translucency of objects in everyday life?
Answer:
Yes, we utilise the transparency, opacity and translucency of objects in everyday life. For example, using clear glass for windows, opaque materials for walls, etc.
Question 19.
Find out more situations through group discussion and present them in the class.
Answer:
Answer:
Question 20.
Can you write a science fiction with a transparent man or any other organism as a character?
Answer:
Hints
- Explain where the transparent character came from. .
- Describe the character’s first response to their transparency.
- Describe how the transparent character was received by society.
- Describe a major conflict with the character’s transparency. Medical complications or privacy issues may be involved.
- Draw attention to the particular difficulties the transparent character encounters.
- Include some action sequences.
- Choose a climax that highlights whether the character maintains their transparency or manages to reverse it.
Question 21.
What happens when light falls on opaque objects?
Answer:
When light falls on opaque objects, it cannot pass through them. It gets reflected back.
Activity
Dim the light in your class room by closing the doors and windows. Hold a mirror facing the wall and let the light from a torch fall on it.
Question 22.
What happens to the light?
Answer:
The light rays fall on the wall after hitting on the mirror.
Question 23.
Haven’t you noticed that the light rays fall on the wall after hitting on the mirror?
Answer:
Yes
Question 24.
Repeat the experiment by holding the following objects against the wall and allowing light from the torch to fall on each of them.
Materials required: smooth tile, new steel plate, bronze, hardboard, paper, wooden block. Record your observations in the table given below.
Answer:
| The object on which light fell | Difference in the returning of light after falling on the surface |
| Mirror | Light returns well |
| Paper | Very little light returns |
| Wooden block | Light does not return |
| Hard board | Light does not return |
| New steel plate | Light returns well |
| Smooth tile | Light returns well |
Question 25.
Touch and feel the surfaces of the objects which reflect light very well. What do you feel?
Answer:
We feel that it is very smooth.
Question 26.
What about the surfaces of objects that do not reflect light much?
Answer:
We feel that it is very rough.
Question 27.
Haven’t you found that smooth surfaces reflect light very well and that it is less in the case of rough surfaces?
Answer:
Yes
Question 28.
Why is it that rough surfaces cannot reflect light well?
Answer:
Rough surfaces cannot scatter light well because they scatter light in different directions. (There are irregularities on a rough surface which makes it difficult for the light rays to get reflected in the same direction.) The reflection of light from a mirror and a sand paper are depicted below.
Question 29.
Analyse the figures and write the inferences.
Answer:
Inference – The light falling on the mirror reflects regularly whereas the light falling on the sand paper reflects irregularly.
Question 30.
Doesn’t the light that fall on the mirror undergo a regular reflection?
Answer:
Yes
Question 31.
What about the light falling on the sandpaper?
Answer:
It undergoes diffused reflection.
Activity – To observe the regular reflection of light
Arrange a comb, a torch, a mirror and a sheet of A4 size paper as shown in the figure below and light the torch.
Observation – The regular reflection of light can be observed.
Regular Reflection
Light falling on smooth surfaces reflects with regularity. This is regular reflection. Mirrors give a regular reflection.
Diffused Reflection
When light falls on rough surfaces, it gets scattered in different directions. This is irregular reflection or diffused reflection.
Activity
Kick a ball to a particular point on a wall from different places.
Question 32.
Doesn’t the ball hit the wall and bounce back?
Answer:
Yes, the ball hits the wall and bounces back.
Question 33.
Does it always bounce back in the same manner?
Answer:
No
Question 34.
Similarly, are there any peculiarities in the light rays falling on and bouncing off a mirror?
Answer:
The light rays falling on and bouncing off a mirror always bounce back in the same manner.
The figure given below shows four children sitting at equal distances on two benches in front of a mirror. Listen to their conversation.
Question 35.
Why is it that the child who is sitting first can’t see those sitting at the second and the third positions?
Answer:
This is because the way in which the light bounces back depends on the angle at which it hits the wall. So, the child can only see the image of people that are in line with the angle at which light reflects.
Question 36.
Similarly, why can’t the other children see all others through the mirror?
Answer:
The mirror reflects light according to the angle at which it hits its surface. So, the other children can’t see all others through it.
Question 37.
Measure the angle between the ray of light from the laser torch and the normal. Similarly Angle between the light ray from the torch and the normal Angle between the reflected light ray and the normal
Answer:
Question 38.
Analyse the completed table. Is there any relation between the angle made by the light ray from the torch with the normal and the angle made by the reflecting light ray with the normal?
Answer:
The angle made by the light ray from the torch with the normal and the angle made by the reflecting light ray with the normal are equal.
Observe the diagram given below.
- The ray of light falling on the mirror is the incident ray.
- The point at which the incident ray falls on the mirror is the point of incidence.
- The line drawn perpendicular to the mirror at the point of incidence is the normal.
- The light ray reflecting from the mirror is the reflected ray.
Angle of Incidence and Angle of Reflection
The angle between the incident ray and the normal is the angle of incidence. The angle between the reflected ray and the normal is the angle of reflection.
Question 39.
What did you find out regarding the reflection of light from the experiment you have conducted?
Answer:
From the experiment, we have found out that the angle at which light hits the mirror (the angle of incidence) is equal to the angle at which it reflects from the mirror (the angle of reflection).
Plane
• The two sheets of paper inserted into each other are on two planes.
• Each wall in your classroom is a plane.
Laws of Reflection
• The angle of incidence and the angle of reflection are equal.
• The incident ray, the reflected ray and the normal at the point of incidence are on the same plane.
Question 40.
How does light reach the eye so that we see the book?
Answer:
Light from the bulb travels in all directions. Some of this light hits the book and reflects from its surface. Some of the reflected light enters the eye and we can see the book.
Question 41.
Observe the picture showing the path of the light ray from the bulb falling on the book and reflecting to our eyes. Complete the flow chart.
Answer:
Question 42.
Haven’t you understood that we see a book when the light falling on it gets reflected and reaches our eyes?
Answer:
Yes
Question 43.
How Do We See Things?
Answer:
We see an object when light coming from any source of light falls on that object, gets reflected and reaches our eyes. But we see a source of light when the light from it reaches our eyes directly.
Question 44.
Don’t we see many beautiful sights every day? How are these sights possible?
Answer:
Yes. When sunlight or the light from sources like bulbs and lamps falls on these beautiful objects, it gets reflected and reaches our. eyes. This is how we can see them.
Question 45.
Haven’t you understood that we see all sights on Earth due to the reflection of light?
Answer:
Yes
Question 46.
Why can’t we see our own face?
Answer:
We see objects when the reflected light reaches our eyes. The light falling on our face will not get reflected to our face. So, we can’t see our face.
Question 47.
We see objects when the reflected light reaches our eyes. Will the light falling on our face get reflected to our eyes?
Answer:
No
Question 48.
What is the device we use to see our face?
Answer:
A plane mirror
Question 49.
What are the different surfaces from which light gets reflected and reaches our eyes while seeing our face in the mirror?
Answer:
Our face and the mirror
Question 50.
Observe the figure and identify the path of light. Complete the flow chart and record it in the Science Diary.
Answer:
Question 51.
On which surfaces other than the mirror, can you see your face?
Answer:
- Smooth steel plate
- Clear water
- Smooth surfaces
Look at the picture below.
Question 52.
Haven’t you seen mirrors of different shapes? What are the peculiarities of the surfaces of these mirrors?
Answer:
Yes
The surfaces of these mirrors have different shapes.
1) Circular
2) Rectangular
3) Oval
Plane Mirror
A mirror with a flat surface is a plane mirror. We can see our images in plane mirrors.
Question 53.
Which hand of the image is raised?
Answer:
Right hand.
Write down your name in English using capital letters on a white paper and show it in front of the plane mirror.
Question 54.
Can you read your name in the mirror?
Answer:
It is difficult to read.
Question 55.
If so, how should the word ‘BASIC SCIENCE’ be written on a paper so as to read it on a plane mirror?
Answer:
Question 56.
Try to write down the names of your friends in such a way that you can read it correctly from a plane mirror.
Answer:
Question 57.
On which side of the image will a mole on one’s left cheek be seen?
Answer:
Right side
Question 58.
What property of the image formed in the plane mirror can be understood here?
Answer:
Lateral inversion
Lateral inversion
In a plane mirror, the left side of an object appears as the right side of the image and the right side of the object appears as the left side of the image. This phenomenon is lateral inversion.
Question 59.
Haven’t you seen this vehicle? What would be the reason for writing like this on the vehicle? Discuss and record it in the Science Diary.
Answer:
Yes.
In the front of the ambulance, the word “AMBULANCE” is written laterally inverted so that when another driver looks in their rearview mirror, the word will appear correctly, and this lets the driver give way for the ambulance.
Distance to the Image
Stand in front of a plane mirror.
Question 60.
At what distance is your image seen?
Answer:
The distance between the person and the mirror is the same as the distance between the image and the mirror.
Question 61.
Move a little forward and backward. Doesn’t the position of the image also change?
Answer:
Yes
If we take reflective glasses used in windows instead of plane mirror, we can measure the distance of an object from the mirror and the distance to the image from the mirror.
Question 62.
What will be the position of the image formed on the mirror?
Answer:
The position of the image of the candle formed on the mirror will also be at the area marked 3, where the coin is placed. (The distance between the object and the mirror will be the same as the distance between the image and the mirror.)
Repeat the experiment, by placing the candle at different positions. Move the coin to the positions where the images are seen.
Question 63.
Is there any relation between the distance to the object from the mirror and the distance to the image from the mirror?
Answer:
Distance of the object from the mirror and the distance of the image from the mirror are equal.
Question 64.
If you look at it from one side, don’t you see both the reflection and the candle on the other side at the same position?
Answer:
Yes
Question 65.
Observe the sizes of both. Compare the size of the object and the image by changing the position.
Answer:
The size of the object and the image remain the same.
Light up the candle on one side of the mirror. Measure the height of the candle upto the tip of the flame using a scale. Similarly, measure the height of the image on the other side with the help of # your friends. Repeat the experiment by changing the size of the candle.
Question 66.
Do the object and the image have the same size?
Answer:
Yes
Characteristics of Images in a Plane Mirror
- The image undergoes lateral inversion.
- In a plane mirror, the distance between the object and the mirror is equal to the distance between the image and the mirror.
- In a plane mirror, the size of the object will be equal to the size of the image.
Question 67.
When a burning candle is placed in front of a plane mirror, we get only one image.How many images will you see if a burning candle is placed in between two parallel plane mirrors? What is your assumption?
Answer:
A large number of images can be seen.
Question 68.
How many images do you see on the mirror on the opposite side? Why do we see such a large number of images?
Answer:
We can see a large number of images. This is due to multiple reflection.
A large number of images of the lighted candle placed in between the parallel mirrors are formed due to multiple reflection of light.
Question 69.
The picture given depicts a situation involving multiple reflection in daily life. Find more examples.
Answer:
- Barber shop
- Shopping malls
- Jewelleries
- Periscope
- Kaleidoscope
Angle between the Mirrors and the Number of Images
Experiment
Glue two plane mirrors of equal size together with cellotape as shown in the above figure. Place a small ball in the middle and observe the number of images formed. Change the angles in between the mirrors.
Question 70.
Observe whether there is a change in the number of images formed.
Answer:
Yes, the number of images formed changes.
Question 71.
Find out the angle between the mirrors and the number of images formed and complete the table.
Answer:
| Angle | Number of images |
| 30° | 11 |
| 60° | 5 |
| 90° | 3 |
| 120° | 2 |
Question 72.
Is there any relation between the angle between the mirrors and the number of images formed?
Answer:
Yes
If the angle is x, then the number of images is \(\frac{360}{x}\) – 1 .
Question 73.
What happens to the number of images when the angle between the mirrors increases?
Answer:
Decreases
Question 74.
What if the angle decreases?
Answer:
The number of images increases.
Question 75.
What do you see?
Answer:
A beautiful, symmetrical patterns of different colours and forms are visible when colourful beads are put inside a kaleidoscope. This pattern changes when the kaleidoscope is rotated.
2) Periscope
Activity – To make periscope
Materials required: A cardboard piece of size 25 cm × 30 cm, two plane mirror pieces of size 3 inch × 2.5 inch (Sunpack sheet can also be used instead of cardboard piece).
Method of construction
Stage 1: Cut a cardboard/sunpack sheet of size 25 cm × 30 cm.
Stage 2: Draw lines on it with the same measure as shown in the figure below.
Stage 3: Cut off the unshaded parts of the figure along the lines. You will get a shape as shown in below figure.
Stage 4: Fold this shape as shown and glue it up.
Stage 5: Cut two pieces of plane mirrors of size 3 inch × 2.5 inch. While fixing them on the slanting ends of the device you have made, make sure that the reflecting surface faces the inner side of the device.
Question 76.
Isn’t it the upper view that we get when we look through the lower end of periscope? Why is it so?
Answer:
Yes. This is because of the mirrors inside the device that reflect light down from the top end to the bottom end.
Question 77.
By observing the path of light shown in the figure, will you be able to explain how this view is possible?
Answer:
Yes. As light from the object strikes the top mirror, it is reflected downward. This light passes through the periscope tube. It is then reflected into your eye horizontally by the bottom mirror.
Question 78.
Discuss how a periscope is useful for the submarines in the Navy and for soldiers observing enemies from trenches in the battlefield.
Answer:
Submarines in the Navy
(a) It allows the crew to see the surface of water even when the submarine remains underwater.
(b) It helps to find enemy ships and other dangers.
For soldiers in trenches
(a) It helps soldiers observe the movements of enemies without exposing themselves.
(b) It also helps to find other dangers.
Question 79.
What if the periscope you have made is similar to the one as shown in the figure? The view from which part can be seen? Try to draw the path of light.
Answer:
Question 80.
Didn’t you notice how worried the owl is?
Answer:
Yes
Question 81.
When do owls go out for preying?
Answer:
At night
Question 82.
How does the intense light at night affect them?
Answer:
Owls are adapted to low light conditions. So, intense light at night can affect their ability to hunt and navigate.
Question 83.
Are the owls alone affected by the artificial light at night?
Answer:
No, many other animals are also affected.
Example – Bats, sea turtles, etc.
The use of light in excess in a non-judicious manner is referred to as light pollution.
Question 84.
Didn’t you realize some problems caused by light pollution? Too much light at night causes many difficulties for human beings as well as animals. Discuss them in the class and record in the Science Diary.
Answer:
- In urban areas the illuminations at night cause people to miss many of the sky views.
- Intense light falling on the eyes may cause blindness.
- Intense light used by motor vehicles causes inconvenience to the drivers on the other head.
- Light at night is harmful to many organisms that prey in the dark.
When Light Reflects Class 7 Notes Extra Questions and Answers
Question 1.
Say whether transparency or opacity is utilized in the following situations.
a) Glass fish tanks are used in aquariums
b) Glass sheets are painted black
c) Curtains are used in hospitals
d) Glasses are used in spectacles.
Answer:
a) Transparency
b) Opacity
c) Opacity
d) Transparency
Question 2.
Classify those given below as transparent, translucent and opaque objects.
a) Window glass piece
b) Butter paper
c) Glass slab
d) Oiled paper
e) Wooden block
f) Metal plate
Answer:
Transparent objects – Glass slab, Window, Glass piece
Translucent objects- Butter paper, Oiled paper
Opaque objects -Wooden block, Metal plate
Question 3.
Identify in which of the following situations regular reflection and diffused reflection takes place.
a) Light from the headlights of vehicle falls on dusty air.
b) Torch light is pointed to misty air.
c) Image of trees seen in the stagnant water.
d) Image of the vehicle behind is seen in the rearview mirror of vehicles.
Answer:
a) Diffused reflection
b) Diffused reflection
c) Regular reflection
d) Regular reflection
Question 4.
Why does a rough surface cause diffused reflection?
Answer:
A rough surface causes diffused reflection because of the irregularities on the surface, which makes the light rays reflect in many different directions instead of in a single direction. It causes light to scatter and spread out.
- A mirror with a flat surface is a plane mirror.
- Lateral inversion means that the left side of an object in a plane mirror appears on the right side and vice versa.
- Distance of object from mirror equals distance of the image from the mirror.
- Size of object equals size of image.
- An object placed between two parallel mirrors produce large number of images due to multiple reflection.
- Kaleidoscope and Periscope are two devices that works on multiple reflection.
- The use of light in excess in a non-judicious manner is referred to as light pollution.
Question 5.
The angle between two plane mirrors is 90°. How many images of a ball placed in front of it will be formed?
Answer:
n = \(\frac{360}{x}\) – 1
x = 90°
n = \(\frac{360}{90}\) = 1
n = 4 – 1 = 3
Question 6.
Does the light reflected from our face reach our eyes and what method do we use to see our own face?
Answer:
The light reflected from our face does not reach our eyes. We use mirrors to see our own face.
Question 7.
Suggest a precaution to be taken by people who are engaged in welding works. Why?
Answer:
They should wear safety glasses. Because the intense light produced during welding is harmful to the eyes.
Question 8.
a) Arrange the given objects as transparent, translucent and opaque.
Water, Butterpaper, glass, wood, stone
b) Explain what are transparent, translucent and opaque objects.
Answer:
a) Transparent: Water, glass.
Translucent: Butter paper
Opaque: Glass, Wood
b) Objects that transmit light very well are called transparent objects. Objects which transmit light partially are called translucent objects. Objects which do not transmit light are opaque objects.
Question 9.
a) Can you write an experiment to make water translucent?
b) Write an experiment to make air translucent.
c) Which of the following is not a transparent object?
(Piece of glass, A plastic bottle, paper)
Answer:
a) Fill 3/4 of a plastic bottle with water. Point light from a torch to it. Light passes through water. Add a few drops of blue ink into water. Repeat experiment. It can be observed that light transmits through it partially indicating that water has become translucent.
b) Take a transparent glass bottle. Point a lighted torch and observe. Light passes through it. Mix some smoke in the bottle by burning incense sticks. Again, repeat the experiment. It can be observed that light transmits partially through it.
c) Paper
Question 10.
a) Choose the wrong statements from the following and correct it ?
i. Glass sheet is a translucent object
ii. Light passes partially through an opaque object
iii. Mixing water with milk makes it translucent
b) Write one example each of situations making use of opacity and transparency of light in daily life.
Answer:
a) i and ii are the wrong statements
i. Corrected statement: Glass sheet is a transparent object
ii. Corrected statement :Light cannot passes through an opaque object
b) Glasses in spectacles make use of transparency Curtains make use of opacity
Question 11.
(a) Identify the type of reflection represented by figure (i) and (ii).
(b) The reflection from a cardboard is an example of
(c) Explain each type of reflection.
Answer:
(a) (i) Regular reflection
(ii) Irregular reflection/ Diffused reflection
(b) Irregular reflection/Diffused reflection
(c) Light falling on smooth surfaces reflects with regularity. This is regular reflection. Mirrors give a regular reflection.
When light falls on rough surfaces, it gets scattered in different directions. This is irregular reflection or diffused reflection.
Question 12.
(a) Draw a diagram to represent reflection of light in a mirror.
(b) Explain the terms
(i) Incident ray
(ii) Point of incidence
(iii) Normal
(iv) Reflected ray
Answer:
(b)
(i) The ray of light falling on the mirror is the incident ray.
(ii) The point at which the incident ray falls on the mirror is the point of incidence.
(iii) The line drawn perpendicular to the mirror at the point of incidence is the normal.
(iv) The light ray reflecting from the mirror is the reflected ray.
Question 13.
(a) Correct the flowchart which shows how we see a flower .
(b) Why can’t we see in a dark room?
Answer:
(a) 
(b) We see an object when light coming from any source of light falls on that object, gets reflected and reaches our eyes. As there is no source of light in a dark room,light does not fall on an object and reflect,hence we cannot see the object.
Question 14.
(a) Complete the table given below.
(b) What is the relation between angle of incidence and angle of reflection?
Answer:
Question 15.
Observe the figure given below
(a) Which are the types of reflection represented by each figure?
(b) Classify the following based on objects producing regular and irregular reflection (mirror, A new steel plate, cardboard, sandpaper)
(c) In which one- an new steel plate or an old steel plate can a person see his face clearly?Why is it so ?
Answer:
(a)
(i) Regular reflection
(ii) Irregular reflection
(b) Objects producing regular reflection-Mirror,A new steel plate
Objects producing irregular reflection- Cardboard,Sandpaper
(c) In a new steel plate because regular reflection takes place therein old steel plate due to its rough surface only a blurred image will be visible.
Question 16.
a) Is there any relation between the distance to the object and the distance to the image from a plane mirror? Design an experiment to prove this relation.
b) Write two peculiarities of the image formed in a plane mirror.
Answer:
a) The distance to the object and the distance to the image from a plane mirror is the same.
Fix a plane mirror vertically on a table using double-sided tape. Place a lighted candle at a certain distance from the plane mirror (say, 3 cm). Repeat the experiment by placing the candle at different positions (say, 4cm, 5cm, etc.,). Observe the position of the image from the mirror. We can observe that the distance to the object and the distance to the image from a plane mirror is the same.
b) Virtual and erect
The size of object and image is the same
Question 17.
Observe the picture.
A. Identify and write the incident ray and reflected ray.
B. Write the measure of angle of reflection:
C. Write any three peculiarities of image formed by a plane mirror.
Answer:
A. AO is the incident ray
OB is the reflected ray
B. Angle of reflection ∠r = 40°
(Angle of incidence ∠i =Angle of reflection ∠r)
C. Virtual and erect
The size of object and image is the same
Image is Laterally inverted
Question 18.
Observe the picture. A child is looking at a mirror in a dark room.
(A) What changes should be made in the settings to see the face of the child clearly?
(B) Explain how the child can see the image on changing the settings?
(C) Write any two peculiarities of the image that the child sees in the mirror.
Answer:
(A) The Lamp should be turned towards the child such that light falls on the child.
(B) The light from the lamp falls on the child and reflects and strikes the mirror. This creates an image of the child in the mirror.
(C) Virtual and erect The size of child and image is the same.
Question 19.
When appu raised his left hand it front of a plane mirror he observed that it appeared as right hand and when he raised the right hand it appeared as left hand .
(a) Is appu’s observation correct?
(b) What is this phenomenon known as ?
(c) Explain the phenomenon?
Answer:
(a) Yes
(b) Lateral inversion
(c) In a plane mirror, the left side of an object appears as the right side of the image and the right side of the object appears as the left side of the image. This phenomenon is lateral inversion.
Question 20.
Regular reflection in a plane mirror is shown below.
(a) Find out the mistakes in it and redraw the correct figure.
(b) What is the angle of reflection if angle of incidence is 45°.
(c) State the law of reflection that helped you to calculate the angle of reflection.
Answer:
(a) 
(b) Angle of incidence = Angle of reflection
Angle of reflection = 45°
(c) The angle of incidence and the angle of reflection are equal.
Question 21.
Rohith observed a number of images of him when he stood in between two parallel plane mirrors in washroom.
(a) Why did he observe many images in this case?
(b) Find out the number of images formed when the mirrors are arranged at an angle of 60°.
(c) What is the angle at which mirror is to be arranged so as to get 3 images?
Answer:
(a) Multiple reflection of light creates many images depending upon the angle between the mirrors. Here mirrors are arranged parallely, so the angle between them is 180°.Number of images formed in this case is infinity.
(b) n = \(\frac{360}{x}\) – 1
x = 60°
n = \(\frac{360}{60}\) – 1 = 5
(c) n = \(\frac{360}{x}\) – 1
n = 3
x = \(\frac{360}{n+1}\)
x = \(\frac{360}{4}\)
x = 90°
Question 21.
(a) Complete the given table
| Angle | Number of images |
| 300 | …..(A)……… |
| 1200 | ……..(B) |
Answer:
(a)
| Angle | Number of images |
| 300 | …..11……… |
| 1200 | ……..2 |
(b) As the angle between mirrors increases, number of images decreases.
Question 23.
Raju while reading a comic book, saw a task to find the correct word.
(a) How can he identify the correct word?
(b) Which of the following shows the wrong representation of image of the letters that appear in mirror when placed in front of a plane mirror.
(c) Writing in front of an ambulance is shown below. Why is it written so ?
Answer:
(a) By placing the word in front of a plane mirror. Lateral inversion helps to identify the correct word.
(b) (iii) is wrong
(c) In the front of the ambulance, the word “AMBULANCE” is written laterally inverted so that when another driver looks in their rearview mirror, the word will appear correctly and this lets the driver to give way for the ambulance.
Question 24.
(A) Identify the devices shown in the figure.
Answer:
(a) (i) Kaleidoscope (ii) Periscope
(b) Kaleidoscope is used to observe the beautiful patterns of objects like (pieces of bangle, papers) placed in it.
Periscope is useful for the submarines in the Navy and for soldiers observing enemies from trenches in the battle field.
(c) In submarines and tanks, a periscope is useful because it lets the crew see above the water or over obstacles while staying hidden and safe. The upper view is possible when viewed through the lower end of periscope due to reflection of light from the mirrors. The light falling at the first mirror at the upper part and gets reflected and reaches the second mirror at the lower part creating the view of the upper part.This helps them find their way, keep an eye on their surroundings, and find their goals without putting themselves in danger.
Question 25.
Raju and Rohith live in a populated city. They went to their terrace to watch the beautiful night sky. But were not able to enjoy a sky view as expected .Rohith told Raju that it was due to light pollution.
(a) Is Rohith right?
(b) What is light pollution?
(c) What are some of the problems caused by light pollution?
Answer:
(A) the is right
(B) The use of light in excess in a non-judicious manner is referred to as light pollution.
(C) Intense light falling on eye may cause problems in vision.
Light at night is harmful to many organisms that prey at night.
Intense light of motor vehicles causes hindrance to other drivers.
Question 26.
Match the following.
| A | B |
| Plane mirror | Translucent object |
| Kaleidoscope | Transparent object |
| Butterpaper | Multiple reflection |
| Glass slab | Lateral inversion |
(b) Analyse the statements given below and correct the wrong statements.
i) Diffused reflection helps to get Sunlight inside rooms.
ii) Surfaces that reflect light irregularly are called mirrors.
iii) Objects that do not transmit light are called translucent objects.
iv) A plane mirror makes a larger image than object.
Answer:
(a)
| A | B |
| Plane mirror | Lateral inversion |
| Kaleidoscope | Multiple reflection |
| Butterpaper | Translucent object |
| Glass slab | Transparent object |
(b)
i) Correct statement
ii) Surfaces which reflect light regularly are called mirrors.
iii) Objects that do not transmit light are called opaque objects.
iv) A plane mirror makes an image of same size of the object.
When Light Reflects Class 7 Notes
- Transparent objects – Objects that transmit light very well. Examples: window glass, pure water taken in a glass tumbler
- Translucent objects – Objects that transmit light partially. Examples: butter paper, polythene cover
- Opaque objects – Objects that do not transmit light. Examples: wooden block, aluminium foil
- Transparent or translucent objects can be made opaque by covering them with paint or soot.
- Transparent objects can be made translucent by adding oil, sooting lightly or painting lightly.
- Transparency and opacity of objects benefit us by allowing us to control light and visibility.
- Oil paper (tracing paper) is commonly used to trace pictures and maps. .
- Reflection of light – The returning of light when it strikes on an object.
- Regular reflection – Light falling on smooth surfaces reflects with regularity.
- Irregular reflection or diffused reflection – Light falling on rough surfaces gets scattered in different directions.
- Incident ray – The ray of light falling on the mirror.
- Point of incidence – The point at which the incident ray falls on the mirror.
- Normal – The line drawn perpendicular to the mirror at the point of incidence.
- Reflected ray – The light ray reflecting from the mirror.
- Angle of incidence – The angle between the incident ray and the normal.
- Angle of reflection – The angle between the reflected ray and the normal.
Laws of reflection
- The angle of incidence and the angle of reflection are equal.
- The incident ray, the reflected ray and the normal at the point of incidence are on the same plane.
- Lateral inversion – In a plane mirror, the left side of an object appears as the right side of the
image and the right side of the object appears as the left side of the image.
Characteristics of images in a plane mirror
- The image undergoes lateral inversion.
- In a plane mirror, the distance between the object and the mirror is equal to the distance between the image and the mirror.
- In a plane mirror, the size of the object will be equal to the size of the image.
Multiple reflection
- A large number of images of the lighted candle placed in between the parallel mirrors are formed due to multiple reflection of light.
- If the angle is x, then the number of images is \(\frac{360}{1}\) – 1