Physics CH 2

St.
Dominic Savios High School
Physics
Chapter- Light
Chapter-11
1 .Define
Luminous body - The objects which emit light of their own are called luminous bodies,
e.g., the sun, the stars, etc.
Opaque objects - Those materials which do not allow light to pass through them, are
called opaque objects. Examples wood, stone, etc.
Translucent object- Those objects which allow only a small part of the light rays to pass
through them are called translucent objects. These are the objects through which one
cannot see properly.
Transparent objects- Those objects which allow light rays to pass through them
completely are called transparent objects. One can see clearly through these objects.
Pinhole Camera- It is a device which forms a photograph like image of a bright object on
a screen
Screen- Screen is a surface on which images are formed.
Mirror- A smooth shining surface, which rebounds the light back in same or in different
direction is called a mirror.
2. DIFFERENTIATE
1. Luminous and Non-luminous objects?
Luminous objects: Objects that give out or emit light of their own, e.g., sun, torch, light,
bulbs, etc.
Non-luminous objects: Objects that do not give out light of their own, e.g., the moon,
chair, shoe, pen, etc.
2. Image and reflection
Image Shadow
1. Image is formed due to reflection or refraction of 1. Shadow is formed when light falls on the opaq
light body.
2. Image is seen when light coming from the object

2. No light enters the eye from the shadow of the
after reflection or refraction enters the observes’s
object.
eye.
3. Shadow does not provide any detail about the

3. Image gives more information such as colour,
object, it gives an idea about the shape of the
structure, etc., about the object
object.
Answer in brief:
Q1.. Classify the following into transparent, opaque and translucent objects:
Wax, spectacles, a heap of salt, a stone, dense smoke, wood, skin, balloon, rubber,
membrane of a tabla, blood and milk.
Ans) Transparent objects are Spectacles.

Opaque objects are A stone, wood, a heap of salt, dense smoke, and membrane of
tabla.
Translucent objects are Blood, milk, wax, skin, balloon, rubber.
Q2. Name sources of light that are not hot.
Ans) Tube light, jugnu.

Q3. List four natural sources of light.
Sun
Stars
Fire
Jugnu (Firefly).
Q4) . Write down four man-made sources of light.
 Candle
 Oil lamp
 Electric bulb
 Torch.
Q5. Does the fire emit light?
Ans. Yes, fire emits light.
Q6. On what factor does the proportion of light that enters an object depend?
Ans. Optical nature of the object.
Q7.Give examples of two substances through which light does not pass?
Ans Wood and bricks are the substances through which light does not pass.
Q8. What do we need in order to see a shadow?
We need
 a source of light,
 an opaque object in the way of light, and
 a screen;
Q9. Does the direction of shadow change during the day? Does the length of shadow
also change from season to season?
Ans. Yes, the direction of shadow changes as the sun changes its position during the
day. The length of the shadow also changes from season to season.
Q10. What is a shadow? How is it formed? How does the colour of an opaque object
affect the colour of the shadow?
Ans- A shadow is a dark outline or image cast by an opaque object that blocks light
coming from a source of light. It is formed when light hits the opaque object which does
not let the light pass through. Everywhere else around the opaque object, the light
continues in a straight path until it bounces off the ground or wall behind the object. The
wall or ground behind the opaque object is the screen. On this screen is a dark patch, or
shadow, with the same outline as the object surrounded by light. The colour of the
opaque object does not affect the colour of the shadow that is formed.
Q11. What is umbra and penumbra?
Ans) Umbra is the dark region behind object facing light which does not receive light at
all.
Penumbra is the less dark part of shadow. It is the outer part of shadow.
.Q 12. Can you think of a situation where we can see the path of the light?
Ans) In a dark room, we can see with torch light which goes straight. Similarly, dust
particles become visible when light enters the room through fine hole.
All these examples indicate that light travels in straight line.
Q13.) Why is the image formed in a pinhole camera inverted?
Ans) In a pinhole camera, image formed is inverted because the object is between
radius of curvature and focus.
.Q14) What is reflection?
When a ray of light falls on a smooth and shiny surface, the whole of light is sent back in
the same medium. It is called reflection. Mirrors do not allow even a small amount of
light to pass through them. Mirrors show regular and complete reflection.
.
Q15) Why is silvered glass used as a mirror?
Ans)The silvered glass has a smooth surface and the smoothness helps in forming
clear image. Silvering makes it shiny and the shiny surface helps in reducing the
absorption.
.
Q16) What happens when light falls on a mirror?
Ans )Mirror is silvered on one side, so it does not allow the light to pass through it. It
reflects almost whole of the light falling on it.
Q17) What change in the path of light takes place when light falls on a shiny surface?
What is this called?
Ans) : The light comes back in the same plan when light falls on a shiny surface. This is
known as reflection of light.
Q18) Why is the moon not considered as a luminous body?
Ans) Moon is a non-luminous body because it shines by reflecting the sunlight falling
on it.
ACTIVITY BASED QUESTIONS

Q1. Fix a comb on one side of a large thermocol sheet and fix a mirror on the other side
as shown in the figure. Spread a dark-coloured sheet of paper between the mirror and
the comb. Keep this in sunlight or send a beam of light from a torch through the comb.
What do you observe? Do you get a pattern similar to that shown in figure?
Fig. Light travelling in a straight line and getting reflected from a mirror
Light travels in straight line and gets reflected from the mirror. Yes, we get a pattern
similar to that shown in the figure.
Q2. Close your eyes while looking towards bright sunshine. Now, cover the eyes with
your palm still keeping them closed. Do you notice any difference? On the basis of this
experience, state whether your eyelids are transparent, translucent or opaque.
Answer:
On the basis of the experience, we observe our eyelids are opaque.
Q3)Sometimes, you are able to see the Sun or the Moon behind the clouds. What can
you say about the ability of such clouds to transmit light? ‘
Answer:
We may say that clouds behave as translucent object.
Q4) How will you convert a transparent glass sheet into a translucent sheet? Suggest
any two ways to do it.
Answer:
1. By smearing a thin layer of oil we may convert a transparent glass sheet into a
translucent sheet.
2. By covering one side of the glass sheet by butter paper.
Q5. Take flowers or other objects of different colours and look at their shadows. A red
rose and a yellow rose, for instance. Do the shadows look different in colour, when the
colours of the objects are different?
Ans- No, the shadows of the different coloured objects are not different.
PRITI
18.7.2021

Physics CH 2

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St.

Dominic Savios High School

Screen- Screen is a surface on which images are formed.

2. Image is seen when light coming from the object

3. Shadow does not provide any detail about the

Ans) Transparent objects are Spectacles.

Q2. Name sources of light that are not hot.

Ans) Tube light, jugnu.

Q4) . Write down four man-made sources of light.

Q5. Does the fire emit light?

Ans. Yes, fire emits light.

Ans. Optical nature of the object.

Q8. What do we need in order to see a shadow?

Q11. What is umbra and penumbra?

Q13.) Why is the image formed in a pinhole camera inverted?

.Q14) What is reflection?

Q15) Why is silvered glass used as a mirror?

Q18) Why is the moon not considered as a luminous body?

ACTIVITY BASED QUESTIONS

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