Samacheer Kalvi 7th Science Term 3 Solutions Chapter 1 Pdf
Tamilnadu Board Samacheer Kalvi 7th Science Term 3 Solutions Chapter 1: Tamilnadu State Board Solution Class 7 Science Term 3 Chapter 1 – Light.
Samacheer Kalvi 7th Science Term 3 Solutions Chapter 1: Overview
Board |
Samacheer Kalvi |
Class |
7 |
Subject |
Science |
Chapter |
1 |
Chapter Name |
Light |
Samacheer Kalvi 7th Science Term 3 Solutions Chapter 1 Pdf
I.) Choose the correct option
1.) Light travels only in a ___. It is because of this property that are formed ___.
a.) curved line, shadows
b.) straight line, shadows
c.) straight line, reflection
d.) curved line and then straight line, shadows
Answer: b. straight line, shadows
Solution:Shadow is formed when light strike an opaque object, that prevent light to pass through them. Light always travels in a straight line.
2.) Light that hits a mirror gets ___.
a.) Transmitted
b.) Reflected
c.) Absorbed
d.) Refracted
Answer: b. Reflected
Solution:A ray of light bounces back when it strike a smooth and polished surface. This is known as reflection of light.
3.) ___Surface reflects the light well.
a.) water
b.) compact disc
c.) mirror
d.) stone
Answer: c. mirror
Solution: Mirror is a smooth and polished surface, thus it will reflect light well than other things.
4.) Light is a form of ___.
a.) matter
b.) energy
c.) medium
d.) particle
Answer: b. energy
Solution:Light is a form of kinetic energy. It helps to make things visible to us.
5.) You can see your image in polished floors, but not in wooden table because
a.) regular reflection takes place in wooden table and irregular reflection in polished floor
b.) regular reflection takes place in polished floor and irregular reflection in wooden table
c.) regular reflection takes place in both polished floor and wooden table
d.) irregular reflection takes place in both polished floor and wooden table
Answer: b. regular reflection takes place in polished floor and irregular reflection in wooden table.
Solution: When light rays strikes smooth and polished surface it results in regular reflection but when light falls on rough surface it leads to irregular reflection..
6.) Choose the translucent substance from the following
a.) glass
b.) wood
c.) water
d.) Clouds
Answer: d. Clouds
Solution: Glass and wood both are opaque Objects. Water is transparent object and clouds are translucent substance.
7.) Reflection occurs , when the light
a.) about to reach a surface
b.) approaches a surface
c.) passes through a surface
d.) None of these
Answer: b. approaches a surface
Solution: Reflection occurs , when the light approaches a surface. The bouncing back of light rays after it falls on a surface is what results in reflection.
8.) Which of the following is the best reflector of light?
a.) plastic plate
b.) plane mirror
c.) wall
d.) paper
Answer: b. plane mirror
Solution: Plane mirror is a best reflector of light that others. It is a polished and smooth surface where light rays easily strike and bounce back.
9.) Sivarajan placed a meter stick in the playground at 7.00 am in the morning. How will the shadow of the stick at noon look in comparison to the one in the morning
a.) There will be no shadow
b.) The shadow will be longer and on the opposite side as the sun
c.) The shadow will be shorter and on the same side as the sun
d.) The shadow will be shorter
Answer: d. The shadow will be shorter
Solution:The shadow of the stick will be shorter at noon as the source of light i.e. the sun at noon will be above the stick than near the horizon like at morning.
10) The image formed by a pinhole camera is in-verted because,
a.) light travels in straight lines
b.) light rays become laterally inverted as they pass through a pinhole camera
c.) light rays pass through the pinhole
d.) light rays get reflected
Answer: a. light travels in straight lines.
Solution: The image formed by a pinhole camera is in-verted because, light travels in straight lines.
11) Which of the following facts explain how shadows are formed?
a.) Light travels in straight lines
b.) Opaque bodies do not allow light to pass through them
c.) Reflection occurs at a smooth surfaces like mirrors
d.) Lateral inversion happens
a.) both A and B
b.) both A and D
c.) both B and C
d.) only A
Answer: a. both A and B
Solution: Shadows are formed when light travels in a straight line. Light rays that cannot pass through opaque object lead to formation of shadow of that object.
II) Fill in the blanks
1.) A plane mirror produces a __virtual__ image.
2.) A _light_ reflection helps us to see the objects.
3.) The light ray gets _reflected_ when it falls on any polished surface.
4.) Sunlight is a blend of __seven_ colors.
5.) The splitting of white light in to seven colors is called _dispersion__.
6.) The moon __reflects__ sun light.
7.) The sunlight can be split into its constituent colors using _prism___.
8.) Reflection of light from rough surface is called __diffuse_ reflection.
III.) Say TRUE or FALSE
1.) The image of right hand in a plane mirror looks like a left hand.
Answer: TRUE
2.) Rainbow is formed by dispersion of which light by water drops.
Answer: TRUE
3.) The image formed by the plane mirror is laterally inverted, hence the image seen through the periscope is also laterally inverted.
Answer: FALSE
Correct Statement : The image formed by the plane mirror is laterally inverted, but the image seen through the periscope is upright.
4.) We see planets because they reflect light from the sun.
Answer: TRUE
5.) We see a book because it reflects the light that falls on its surface.
Answer: TRUE
6.) The image formed in a pinhole camera is always inverted.
Answer: TRUE
7.) The image formed in a pinhole camera is always the same size as the object.
Answer: FALSE
Correct statement : The image formed in a pinhole camera may not be equal to the size of the object.
8.) The image formed in a plane mirror is upside down.
Answer: FALSE
Correct statement : The image formed in a plane mirror is erect.
9.) A plane mirror is opaque.
Answer: TRUE
10.) A shadow is formed on the same side of the object as the source of light.
Answer: FALSE
Correct Statement : A shadow is formed on the opposite side of the object as the source of light.
11.) we are able to see things around us with the help of regular reflection.
Answer: FALSE
Correct Statement : we are able to see things around us with the help of irregular refection.
12.) After passing through a prism, white light splits into a band of seven colours.
Answer: TRUE
IV.) Match the following
Answer:
1. Rectlinear propagation | Pinhole camera |
2. Plane Mirror | Periscope |
3.Fire fly | luminous object |
4.The Moon | Non-luminous object |
5. Wide light source | Penumbra |
6.Regular reflection | Glossy surface |
7. The sun | Primary source of light |
8. Band of seven colors | Spectrum of light |
V.) Answer the following questions in short
1.) With the help of a diagram, state the laws of reflection
Answer:
Laws of reflection:
1.) The angle of incidence is always equal to the angle of reflection. Li = Lr
2.) The incident ray, the reflected ray and the normal at the point of incidence lie on the same plane.
2.) Figure shows a pencil placed above a mirror
a.) Draw its image formed by the mirror
b.) Show how light rays from the object are reflected at the mirror to form the image for the eye.
Answer: a)
3.) A person is looking at the image of a tree in a mirror placed 3.5 m in front of him. Given that the tree is at 0.5 m behind his eyes. Find the distance between the image of the tree and his eyes. What are needed to see an object?
Answer: Distance between the person and the mirror = 3.5 m
Distance between the person and tree (object) = 0.5 m
The image formed in the mirror =3.5+0.5= 4 m
The distance between the image of the tree and his eyes = 4 + 3.5 = 7.5m
4.) What are luminous objects?
Answer: All objects which emit light energy by themselves are called luminous objects .Eg- Sun, stars
5.) Is the moon a luminous object?
Answer: No, the moon is not the luminous objects , because it cannot produce light of its own.
6.) What are the three types of materials based on the absorption of light?
Answer: The three types of materials based on the absorption of light are
1) Transparent Material
2) Translucent Material
3) Opaque Material
7.) What are the parts of shadow?
Answer: Umbra and Penumbra are the parts of shadow.
8.) What are the properties of shadow?
Answer: Properties of shadow are :
1.) Shadows are formed only by opaque Objects.
2.) Shadow appears in opposite side of light source.
3.) It only shows the outline of an object and other characteristics of an object cannot be determined by it’s shadow.
4.) The shadow will be always be dark in colour.
9.) What is plane mirror?
Answer: A plane mirror is a mirror with a flat reflective surface. A plane mirror makes an Image of objects in front of it.
10.) What is prism?
Answer: A prism is an object made up of a transparent material, like glass or plastic that has at least two flat surfaces that from an acute angle (less than 90° degrees).
11.) What do you mean by visible light?
Answer: Visible light is a spectrum of a number of waves with different wavelength range from 400nm to 700nm (1nm = 10-9 metre) each wave has a definite wavelength represents a particular color. The band of visible light is VIBGYOR.
12.) Write the items given here in the correct column (Stars, brick walls, plants, mirror, planets, electric light bulb,candle)
Answer :
Sources of Light | Objects that reflect light |
Stars | Brick walls |
Electric light bulb | Plants |
Candle | Mirror |
Planets |
13.) A boy of height 1m 45 cm is standing in front of a long mirror at a distance of 2 m.
From this information, fill up the following sentences:
a.) The distance between the boy and his image is __4m__.
b.) The height of the image is __same__.
c.) When the boy moves 1m forward, the distance between her and her image is __2m__.
14.) Draw a diagram of a pin hole camera showing the rays of light passing between the Object and its image
Answer:
15.) Why is the writing on the front of an ambulance back to front as shown in the picture?
Answer:The word “ambulance” is written back to front as due to lateral inversion the drivers see the word in the right way in their rear-view mirror. Lateral inversion is a phenomenon where the left hand side of an object appears to be right hand side of the object and vice versa.
16.) Explain with examples, why some capital letters look the same in a mirror but others are reversed.
Answer: Image formed in the mirror is laterally inverted.
However, some capital letters appear the same in the mirror because they have same left and right sides.
17.) Two plane mirrors M1 and M2 are placed perpendicular with each other, as shown in figure. The ray AB makes an angle 39 ° with the plane mirror M1, then
1.) The reflected rays are ____ , _____
2.) The incident rays are ____ , ____
3.) What is the angle of incident corresponding to the ray BC?
4.) What is the angle of reflection corresponding to the ray CD
Answer: 1.) The reflected rays are _BC_ , CD.
2.) The incident rays are _AB_ , _BC_.
3.) Li = 39°
4.) Lr= 39°
18.) Rajan was playing with the mirror images of a clock. He looked at the clock in his room. It was showing 1:40. Draw the position of the hands on the real clock and on its mirror reflection. Write below the picture what time each picture is showing.
Answer:
19.) What is reflection of light?
Answer: The bouncing back of light from a reflecting surface of an object is called as reflection of light.
Types of reflection :
a) Diffuse reflection – Rough surface
b) Specular reflection – Smooth surface.
20.) If a ray of light is falling on a plane mirror at an angle of 500 is formed, what will be the angle of reflection?
Answer:
Angle of incidence Li = 90° -50°
Li = 40°
Angle of incidence = Angle of reflection
According to laws of reflection,
Li = Lr
Li= 40° :. Lr – 40°
Angle of reflection Lr= 40°
21.) What do you mean by lateral inversion?
Answer: The phenomenon due to which left hand side of object appears as right hand side and vice versa is called lateral inversion.
22.) How do you obtain a spectrum of light?
Answer: When white light is passed through a prism we can obtained a spectrum of light. The spectrum refers to the colours of the rainbow (VIBGYOR) that is emitted from the prism.
23.) Why do we see white color in Newton’s disc, when we rotate it very fast?
Answer: The Newton’s disc appears white when it is rotated fast as the retina receives the sensation of the spectrum simultaneously.
Reason:
When light ray of particular wavelength (colour) fall on the retina of our eye, our brain perceives that specific colour. But When all colours of visible light fall on the retina of our eye at the same time, our brain perceives white.
24.) What is a shadow? What things are necessary for the formation of a shadow?
Answer:
A shadow refers to a dark area that is formed when light rays are obstructed from passing through an opaque objects.
Things necessary for the formation of a shadow:
- Source of light
- Opaque Objects
VI.) Answer the following questions in detail
1.) What are regular and irregular reflection ? Explain with the help of diagrams.
Answer: Regular reflection (specular reflection):
If the surface is smooth then we have specular reflection. The parallel light rays striking the surface gets reflected, yet individual reflected rays remain parallel.
Irregular reflection (diffuse reflection):
If the surface is rough, then we have diffused reflection. Light rays, after reflection go in many directions.
2.) What are the difference between luminous and non-luminous objects? Give two examples of each.
Answer :
Luminous objects :-
|
Non-luminous objects:-
|
Luminous object refers to those object that emit light energy by themselves. | Non-luminous object refers to those object that donot emit light energy by themselves but when light rays fall on them,they reflect them. |
Ex: Sun, stars, torch light, burning candle etc. | Ex: Metals, trees, houses, stones, moon etc. |
3.) Write about two everyday situations that tell you that light travels in a straight line.
Answer: Examples of everday situations to show that light travels in a straight line are :
- Torch light
- In cement grill light travels through the holes.
- Penetration of light through trees.
- Laser beam
4.) Differentiate between a reflection and a shadow.
Answer:
Reflection |
Shadow |
1.Reflection occurr when light rays stike a smooth surface and bounce back. | 1.Shadows are formed when light rays are prevented from passing through certain objects. |
2. The reflected rays help in the formation of an image. | 2. Shadows are formed through opaque objects. |
3. In reflection the image formed is of the same size as that of the object. | 3.Shadow only shows the outline of the object placed infront of the light source. |
5.) What are the characteristics of an image formed in a plane mirror?
Answer: Characteristics of an image formed in a plane mirror :
- The image formed in a plane mirror is upright.
- The size of the image is same as that of the object.
- It a virtual depiction of an object.
- The image formed is laterally inverted.
- The distance of the object from the mirror is equivalent to the distance of the image from the mirror.
6.) Describe the pictures.
Answer: 1. When the tube is bent, we cannot see the source of light.
2.When the tube is held straight we can see the flame.
3.The two pictures verify that light travels in straight lines. This is known as rectilinear propagation of light.
7.) Define the following terms
a.) Incident ray
b.) Reflected ray
c.) Normal
d.) Angle of incidence
Answer: a) Incident ray:- The ray of light that falls on the surface of the reflecting surface is called incident ray.
b) Reflected ray:- The ray of light that comes from the point when the incident ray falls on the reflecting surface is called reflected ray.
c) Normal:- The perpendicular line drawn from the point of incidence to the plane of reflecting surface is called normal.
d) Angle of incidence:- The angle formed between the incident ray and the normal ‘i’ is angle of incidence. It is denoted by Li.
8.) Compare the images formed by plane mirror with that by pinhole camera
Answer:
Images formed by Pin hole camera:- |
Images formed in Plane mirror:- |
a) The image formed is real. | a) The image is virtually formed. |
b) The size of the image is different from the size of the object. | b) The size of the image is equal to the size of the object. |
c) The formed image is inverted. | c) The formed image is erect. |