Samacheer Class 7 Science - Light

1. A. regular reflection takes place in wooden table and irregular reflection in polished floor
2. B. regular reflection takes place in polished floor and irregular reflection in wooden table
3. C. regular reflection takes place in both polished floor and wooden table
4. D. irregular reflection takes place in both polished floor and wooden table

(b) regular reflection takes place in polished floor and irregular reflection in wooden table

1. A. Light travels in straight lines
2. B. Opaque bodies do not allow light to pass through them
3. C. Reflection occurs at a smooth surfaces like mirrors
4. D. Lateral inversion happens
5. A. both A and B
6. B. both A and D
7. C. both B and C
8. D. only A

(a) both A and B

False
Correct statement: The image formed by the plane mirror is laterally inverted, hence the image seen through the periscope is This is because in periscope, image is reflected by two mirrors.

1.
Rectilinear propagation
Pinhole camera
2.
Rectilinear propagation
Periscope
3.
Plane Mirror 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

Laws of reflection:

The angle of incidence is always equal to the angle of reflection li =l*
The incident ray, the reflected ray and the normal at the point of incidence lie on the same plane.

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 = 4 m
The distance between the image of the tree and his eyes = 4 + 3.5 = 7.5

Properties of shadow:
All objects do not form shadows. Only opaque objects form shadows.
Shadows will be formed in the opposite side of light source.
It cannot be determined the characteristics of an object by its shadow.
The shadow will be always darker, whatever may be the color of light rays.
Light source, opaque object are shadow all are in a straight line.
The size of shadow depends upon the distance between light source and object and the distance between object and the screen.

Visible light is a spectrum of a number of waves with different wavelength range from 400nm to 700nm (lnm = 10″9 meter) each wave has a definite wavelength represents a particular colour.

1. A. The distance between the boy and his image is ______
2. B. The height of the image is ______
3. C. When the boy moves 1 m forward, the distance between her and her image is ______

(a) The distance between the boy and his image is 4m
(b) The height of the image is same.
(c) When the boy moves 1 m forward, the distance between her and her image is 2m.

This is due to lateral inversion.
The phenomenon due to which the left side of an object appears to be right side of the object in its image in a reflecting medium (mirror).
So that drivers see the word the right way around in their rear-view mirror.

Angle of incidence \(\lfloor i\) = 90° – 50°
\(\lfloor i\) = 40°
According to laws of reflection,
\(\lfloor i\) = \(\lfloor k\)
Angle of incidence = Angle of reflection
\(\lfloor i\) = 40°
∴ \(\lfloor r\) – 40°
Angle of reflection \(\lfloor r\) = 40°

When the disc turned quickly, the retina receives the sensation of the spectrum simultaneously and disc appears white.
Question 24
What is a shadow? What things are necessary for the formation of a shadow?
Shadows are formed because light travels in straight lines.
Shadow is always against, opposite side of light source.
Shadow is formed by opaque objects that stop high from propagating.
Things necessary for the formation of shadow: source of light,opaque object

(i) Regular reflection When a parallel beam of light on striking some smooth and polished surface is reflected as a parallel beam of light, such a reflection is called regular reflection.

(ii) Irregular reflection : When a parallel beam of light, on striking some rough surface, is reflected in different directions, then such a reflection is called irregular or diffused reflection.

Luminous objects
Non-luminous objects
1.
All objects which emit light energy by themselves are called luminous objects.
All objects which do not emit light energy of their own, but reflect the light energy falling on them and hence, become visible are called non- luminous object.
2.
Ex.: Sun, stars, torch light, burning candle etc.
Ex.: Metals, trees, houses, stones, moon etc.

Formation of shadow: Shadows are formed when some light rays continue its travel in straight lines while other rays are stopped by an object.
When there is a small hole in a room, light travels only in a straight line.

Reflection
Shadow
When light falls on a surface, the direction of ray is changed. This change in direction is known as reflection of light.
Shadow is an image formed by obstruction of light.
Eg.: You see your reflection in a pool of water or mirror.
Eg.: If you place your hand in front of a candle, you will see the image of the hand on the wall. This image will show only the outline of the object placed in front of the light source.

Image formed in a plane mirror is upright.
Image formed in a plane mirror is virtual The image is of the same size as the object
The distance of the image from the plane mirror is equal to the distance of the object from the mirror.
Image is laterally inverted.

1. A. Incident ray
2. B. Reflected ray
3. C. Normal
4. D. Angle of incidence

(a) Incident tavi The ray of light that falls on the surface of the reflection materials.
(b) Reflected ray: The ray of light that comes from the point when the incident ray falls on the reflection material.
(c) Normal: The perpendicular line drawn from, the point of incidence to the plane of reflecting surface is called normal.
(d) Angl e of incidence The angle formed between the incident ray PO and the normal ‘ON’ is angle of incidence.

Difference between the images formed in Pinhole camera and Plane mirror:
Image formed by Pin hole camera
Images formed in Plane mirror
The image is real.
The image is virtual
The image may not be equal to the size of the object
The image is equal to the size of the object
The image is inverted
The image is erect