Selina Concise Class 6 Physics Solution Chapter No. 5- ‘Light’ For ICSE Board Students.
Short Answer Questions Solution:
(1) Write true or false for each statement:
(a) The moon is a natural source of light.
(b) The moon is self luminous.
(c) We can see an object through an opaque medium.
(d) Light passes through glass.
(e) Light travels in a straight line path.
(f) Image formed in a pin hole camerais real.
(g) The image in a pin hole camera gets blurred if the hole is made bigger.
(h) A shadow is formed because light travels in a straight line path.
(i) Solar eclipse occurs when the sun comes in between the earth and the moon.
(j) If the shadow of earth falls on the moon, the eclipse is called lunar eclipse.
(2) Fill in the blanks Solution:
(a) Light gives us the sensation of ____
(b) The sun is a _____ source of light.
(c) A medium through which light cannot pass is called the ______
Ans. Opaque medium.
(d) A medium which allows light to pass through it easily is called the ______
Ans. transparent medium.
(e) Moon is a _____ body.
(f) Light travels in a _____ path.
Ans. straight line
(g) In a pin hole camera, the image formed is ______
Ans. inverted and real
(h) The darkest portion of a shadow is called the _______
(i) The less dark portion os a shadow is called the _____
(j) Lunar eclipse occurs when the ____ comes in between the ______ and the sun.
Ans. earth, moon.
(3) Match the following Answer:
Ans. (a) – (iii), (b) – (iv), (c) – (v), (d) – (ii), (e) – (i)
(4) Select the correct alternative:
(i) The natural source of light is-
(a) candle flame
(b) electric lamp
(d) Kerosene lamp
(ii) The formation of inverted image in a pin hole camera shows that
(a) light enables us to see.
(b) light travels in a straight line path.
(c) light can pass through the pin hole
(d) light does not pass through the pin hole.
(iii) The luminous body is
(a) a lighted bulb
(iv) Umbra is a region of
(a) complete darkness
(b) partial darkness
(c) complete brightness
(d) partial brightness
(v) Penumbra is a region of
(a) complete darkness
(b) complete brightness
(c) partial brightness
(d) none of the above
(vi) Solar eclipse occurs on
(a) every new moon’s day
(b) certain new moon’s day
(c) every full moon’s day
(d) certain full moon’s day.
(vii) Lunar eclipse occurs on
(a) every full moon;s night
(b) certain full moon’s night
(c) every new moon’s day.
(d) certain new moon’s day
Short/ Long Answer Questions Solution:
1)WHAT IS LIGHT? DEFINE IT.
ANS:- Light is a form of energy which affects our eyes to produce the sensation of vision.
2)HOW DOES LIGHT MAKE AN OBJECT VISIBLE?
ANS:-An object becomes visible to us when the light after striking the object gets reflected and reaches our eyes. Light itself is not visible, but light makes object visible to us. Light is therefore a vital and useful requirement of our life.
3) NAME TWO NATURAL SOURCE OF LIGHT.
ANS:- The two natural source of light is sun,stars etc.
4)LIST TWO ATIFICIAL SOURCES OF LIGHT.
ANS:- Two artificial sources of light are Electric bulb,candle etc.
5)DIFFERENCE BETWEEN THE LUMINOUS AND NON LUMINOUS BODIES. GIVE TWO EXAMPLES OF EACH.
ANS:- The differences between-
Luminous- The bodies that have light of their own e.g. sun stars,candle,bulb, oil lamp,torch etc
NON LUMINOUS- The bodies of which do not have their own light that is moon, table,chair. When light falls them then its all are visible.
6)IS THE MOON A LUMINOUS OBJECT?
ANS:- Moon is not a luminous body. It has no light of its own.
7)WHAT DO WE CALL A BODY THATSHINES OF ITS OWN?
ANS:- The body that shines of its own is called a luminous object.
8)WHAT DO WE CALL AN ELECTRIC BULB PRODUCING LIGHT?
ANS:- Luminous object.
9) WHAT IS A TRANSPARENT MEDIUM?
ANS:- A medium that’s allows the pass of light through it easily is called a transparent medium.
10) EXPLAIN THE DIFFERENCE BETWEEN A TRANSPARENT, A TRANSCULENT,AND AN OPAQUE MEDIUM. GIVE TWO EXAMPLES OF EACH.
ANS:- TRANSPARENT MEDIUM:- A substance or medium is said to be a transparent if light passes through it easily. The object can be distinctly seen across a transparent medium. Examples:- Glass, air, water.
TRANSCULENT MEDIUM:- A substance is said to be a transculent if it allows only a part of light to pass through it. Examples:- Tracing paper, waxed paper,greased paper.
OPAQUE MEDIUM:- A substance is said to be opaque if it does not allow any light to pass through it. We cannot see the object through an opaque. Examples:- Butter paper, black paper etc.
11) WHAT DO WE CALL A SUBSTANCE THROUGH WHICH WE CANNOT SEE LIGHT? GIVE AN EXAMPLE OF SUCH A SUBSTANCE.
ANS:- A substance through which we cannot see light is called an opaque medium.
Examples:- Wood,metals,butter paper etc.
12) WHAT DO WE CALL A SUBSTANCE THROUGH WHICH LIGHT PASSES? GIVE AN EXAMPLE OF SUCH A SUBSTANCE.
ANS:- A substance through which light passes is called a transparent substance. Example:- Glass, air etc.
13) CAN A TRANSPARENT MEDIUM FORM AN IMAGE? EXPLAIN YOUR ANSWER.
ANS:-NO, a transparent medium cannot form an image. All the light that passes through a transparent medium completely pass through the substance. For the formation of image it is said that the light rays get reflected through the surfaces.
16) WHAT DO YOU MEAN BY “RECTLINEAR PROPAGATION OF LIGHT”?
ANS:- Light travels in a straight line. This is called the rectilinear propagation of light.
17) DESCRIBE AN EXPERIMENT TO SHOW THAT LIGHT TRAVELS IN A STRAIGHT LINE PATH.
ANS:- Take three cardboards squares of equal size . locate the centre of each piece of cardboards. Take a pin and make a small hole in each cardboards at the same height.then pass a string through the holes and pull it taut. This makes the three holes in a straight line . now take out the string. Place a lighted candle near one of the cardboards. Look at the candle flame from the other side of the other cardboard. The candle flame is clearly seen. Now slightly displace one of the cardboards so that the holes no longer remain in a straight line. Again look at the candle flame from the other side of the any othe cardboard. Then you do not see the candle flame. The reason is that light travels in a straight line.
So we can say that light travels in a straight line path called the rectilinear propagation of light.
19) NAME A SIMPLE APPLICATION OF THE RECTILINEAR PROPAGATION OF LIGHT.
ANS:- The simple application of rectilinear propagation of light are pin hole camera,formation of shadows and elipses.
22) state two factors which affect the size of image formed in a pin hole camera.
ANS:- The two factors which affect the size of image formed in a pin hole camera are-
- The distance of the object in front of the pin hole.
- the distance of screen from the pin hole.
23) IS THE IMAGE OBTAINED IN A PIN HOLE CAMERA ERECT OR INVERTED? GIVE REASON FOR YOU ANSWER.
ANS:- The image obtained in a pin hole camera is inverted. The reason is that the light travels in straight line path. So light from the upper point of the candle passes through the pin hole and strikes the tracing paper in the lower point. Similarly light from the lower point of the candle passes through the pin hole and strikes the tracing paper at the upper point.
24) HOW IS THE IMAGE AFFECTED IN A PIN HOLE CAMERA WHEN ANOTHER FINE HOLE IS MADE NEAR THE FIRST PIN HOLE?
ANS:- If another pin hole is made near the first pin hole, two images are formed on the screen, one due to each of the two pin holes. If the holes are very close, the two images tend to overlap each other. As a result a blurred image will be seen.
25) STATE THE AFFECT ON THE IMAGE IN A PIN HOLE CAMERA IF:
A) THE HOLE IS MADE BIGGER.
B) THE LUMINOUS OBJECT IS MOVED TOWARDS THE PIN HOLE.
C) THE LENGTH OF THE PIN HOLE CAMERA IS INCREASED.
ANS:- A) If the hole is bigger than pin hole a blurred image is seen. The reason is that a bigger hole is equivalent to a large number of pinholes. Each pin hole produces one image. These images overlap each otherresulting in a blurred image.
B) if the object is moved towards the pin hole the size of the image incrases.
c) When the length of the pin hole camera is increased. Then the size of the images also increases.
26) WHAT IS SHADOW? GIVE A REASON FO ITS FORMATION.
ANS:- When light falls on an opaque object,light is obstructed and a dark patch on a screen kept behind is called shadow. This is because light propagates in a straight line. If distance between object and screen is less the shadow will be dark and smaller. If the distance is increased shadow will be dim and larger.
28) STATE TWO DIFFERENCES BETWEEN AN UMBRA AND A PENUMBRA.
ANS:- The difference between the umbra and penumbra is
Umbra:- it is the portion of shadow where no light reaches from the source of light due to the opaque object. It is a completely dark.
Penumbra:- It is the portion of shadow where the portion of light from the source of light reaches the shadow even in the presence of the opaque object in between them. It is not completely dark but is less bright.
29) Same Diagram of 27 No. Question
32) STATE THE CONDITIONS WHEN ONLY THE PENUMBRA OF AN OPAQUE OBJECT IS OBTAINED ON THE SCREEN.
ANS:- If the size of source of light is bigger than the size of the opaque object ,the size of umbra is very small. If the screen is moved away fom the object the umbra vanishes and only the penumbra remains.
33) WHY IS IT THAT THE BIRDS FLYING IN THE SKY DO NOT CAST THEIR SHADOW ON THE EARTH?
ANS:- We do not see the shadow of a bird flying high up in air because in their shadow the umbra is absent and the penumbra is large and faint so That it is not visible as the distance of screen is very large from the object.
34) WHY ARE SHADOWS AT NOON SHORTER THAN IN THE MORNING Or IN THE EVENING?
ANS:- Shadows are shorter at noon than in the morning because at noon the sun is directly overhead. So the sun rays fall vertically on the body.Hence the shadow is very short. In the morning and evening th sun rays fall in an inclined position. So the shadow are long.
35) WHAT IS AN ECLIPSE? NAME THE TWO TYPES OF ECLIPSE.
ANS:- Eclipses are the examples of formation o shadow in nature. There are two kinds of eclipses-
1.Lunar eclipses 2. Solar eclipses.
Lunar eclipse is due to the formation of shadow of earth on moon and solar eclipse is due to the formation of shadow of moon on earth.