REVISION PPT FOR SA II

CLASS VI

LIGHT, SHADOWS AND REFLECTION

PREPARED BY

VIKRANT V. PURANDARE

1) Name the most important source of light for the earth.

sun

2) Name two natural sources of light and two man-made sources of light.

Natural sources of light: Sun, Stars

Man-made sources of light: Tube-light, torch

3) Give one example each of an object:

a] through which we can see clearly.

Glass

b) through which we can see but not clearly.

Ground glass

c) through which we cannot see at all.

Cardboard

4) What type of screen is used in pinhole camera?

Translucent

5) On what principle does a pinhole camera work?

The pinhole camera works on the principle that light travels in straight line.

6) Define:

The property of light travelling in a straight line.

a) Rectilinear propagation of light:

b) Light:

It is an electromagnetic rays that we can detect and enable us to see objects around us

6) Differentiate between luminous and non-luminous objects:

The objects that do not produce their

own light

The objects that produce their own

light

Non luminous Luminous

Ex. The sun, stars, bulb Ex. Table, tree, chair

7) Differentiate between divergent and convergent rays. Draw diagrams to support your answer

Divergent rays Convergent rays

In a beam of light from a small source, the rays are moving away from each other

In a beam of light from a very large source,

the rays of light meet at a common point

Divergent rays Convergent rays

8) Give reasons for the following:

ii) We should not look directly at solar eclipse.

This is because sound waves need a medium like air to travel.

i) We can not hear sound of a ringing bell which is kept in a vacuum jar.

Because this can cause permanent eye damage or blindness.

iii) Sky appears illuminated during the day.

It is due to the multiple deflections of light.

iv) We are not able to see things behind a wall.

This is because wall is an opaque object which does not allow light to pass through it..

v) The image obtained by a pinhole camera is always inverted.

Light always travels in a straight line. So the light rays coming from the top and bottom of the object cross-over (or intersect) at the pinhole.

vi) Grass looks green in colour.

Grass looks green in colour because it absorbs all colours except green, it reflects back the green colour that is received by our eyes .

9) What is pinhole camera? What type of image is obtained on a pinhole camera?

It is a simple device to show that light travels in a straight line. The image obtained on a pinhole camera will always be vertically and

horizontally inverted.

vii) Why shadows are black in colour?

It is because an opaque object does not allow light to pass through it.

Light travels in a straight line. It does not bend round the edges of an

object.

so, no light could reach behind the object and form a dark patch.

10) Differentiate between transparant, translucent and opaque materials. Give suitable examples.

TranslucentTransparent Opaque

A material that allows most of the light to pass through it

A material that allows only a part of light to pass through it

A material that does not allow any

light to pass through it

Ex. Air, pure water, glass

Ex. Tracing paper, wax, ground glass

Ex. Wood, mud, bricks

11) What is shadow? What are the three things required to form a shadow?

A source of light.

An opaque object (to obstruct the path of light)

A screen on which the shadow can be seen.

A dark area formed behind an object where light cannot reach.

We require three things to observe a shadow:

Umbra Penumbra

11) Diffreentiate umbra and penumbra

The dark part of the shadow is called umbra

The partially dark patch is called penumbra

It does not receive any light from the source

It is less dark because it receives only some amount of light

12) Observe the given diagram and answer the following questions:

i) Which property of light is shown in the given diagram?

The above activity shows that light always travels in a straight line.

ii) What will happen if you shift B cardboard a little? WHY?

We can not see the flame of a candle.

If we shift B cardboard a little light will not reach to us

Exact replica of the object and gives all the details

14) Differentiate between image and shadow.

Does not have colour they are only black or grey

Shadow shows only the outline of the object

Image is the same colour as the object

SHADOW IMAGE

It is formed when light is blocked

It is formed due to reflection of light

Shadows doesn't display lateral inversion of the object

Image displays lateral inversion

14) Write any three differences between lunar and solar eclipse .

Lunar eclipse Solar eclipse

i) A lunar eclipse occurs when the earth passes between the moon and the sun

i) A solar eclipse occurs when the moon passes between the earth and the sun

ii) The earth casts its shadow on the moon

ii) The moon casts its shadow on the earth

iii) Lunar eclipse occurs on a full moon day

iii) Solar eclipse occurs on a new moon day

Lunar eclipse

Solar eclipse

15) What do you mean by reflection? How does a plane mirror form an image?

Reflection: The bouncing off and change in direction of light on striking a plane mirror is termed as reflection.

A plane mirror reflects most of the light that falls on it. So, when light from an object falls on a plane mirror, it is reflected away. When the light reflected by the mirror enters our eyes, we see an image of the object in the mirror.

THANK YOU