Light, shadows and reflections

 

A.VERY SHORT-ANSWER QUESTIONS : Answer in one-word

Q.1. Name one man-made luminous body.

Ans. Electric lamp.

Q.2. Is grounded glass transparent ? If not, what type ofsubstance it is ?

Ans. No. It is translucent.

Q.3. Are stars luminous or nonluminous ?

Ans. Luminous.

Q.4. Can a transparent object cast shadow ?

Ans. No.

Q. 5. What will be the colour of shadow of a coloured object ?

Ans. Dark blackish-grey.

Q. 6. Which of the two image or shadow, is formed by light reflected from the object ?

Ans. Image.

B. SHORT-ANSWER QUESTIONS : Answer in 10-15 words

Q. 1. What is light ? Is the speed of light greater than the speed of sound ?

Ans. Light is a form of energy which causes the sensation of vision in our eyes.

Yes, the speed of light is greater than the speed of sound.

Q. 2. Why nonluminous bodies become visible when light from some other source is made to fall on them ?

Ans. When light from some other source is made to fall on nonluminous bodies they become visible due to the reflection or scattering of light falling on them.

Q. 3. What equipment or materials are needed to show the formation of shadow ?

Ans. The equipment needed to show the formation of shadow are a source of light, an opaque object and a screen or surface behind the object.

Q. 4. Write any two characteristics of a shadow.

Ans. (i) Shadow is formed when light falls on an opaque object.

(ii) Shadow doesn’t provide any detail of the object. It only gives an idea about the shape of the object.

Q. 5. Write one advantage and one disadvantage of a pinhole camera.

Ans. Advantage : The image obtained from pinhole camera is free from spherical and chromatic aberration.

Disadvantage : Pinhole camera cannot be used for studying moving objects.

C. LONG-ANSWER TYPE QUESTIONS : Answer in 20-25 words

Q. 1. Write the conditions required for a shadow to form.

Ans. Conditions required for a shadow to form : (i) Shadow is formed when light is made to fall on an opaque object.

(ii) Shadow is formed only if there is a surface or a screen behind the object.

Q.2. What is meant by reflection of light ?

Ans. The phenomenon in which a ray of light after falling on asmooth polished surface or a mirror bounces back to the same medium is called reflection.

Q. 3. Can you think of creating a shape that woul.d give acircular shadow if held in one way and a rectangular shadow if held in another way ?

Ans. Yes, we can think of creating a shape that would give a circular shadow if held in one way and a rectangular shadow if held in another way. If we held a cylindrical cardboard in front of source of light, it will create a round shadow on the ground and if we turn it at some other position, then it creates a rectangular shadow.

(a)  Circular shadow with cylinder

 

(b) Rectangular shadow with cylinder

 

Q.4. Show the reflection of light by a plane mirror.

Ans. 

Q. 5. Differentiate between the image and the shadow of an object.

Ans.

S. No.	Image	Shadow
1	Image is formed due to the reflection or refraction of light	Shadows are formed when opaque objects obstruct the path of light.
2	Image is seen when light comes from the object after reflection or refraction enters the observer's eye.	No light enters the eye from the shadow of the object.
3	Image gives more information such as colour, structure, etc. about the object.	Shadow does not provide any details about the object but it gives an idea about the shape of the object.

 

D. TICK (4) THE ODD-ONE OUT GIVING REASON

1. Sun, Stars, Earth, Jugnu

2. Wood, Iron sheet, Glass, Rocks

3. Rock, Mirror, Iron plate, Plywood

4. A source of light, An opaque object, A plane mirror, A screen

5. Solar eclipse, Pinhole camera, Rectilinear propagation of light,

Reflection from mirror

Ans. 

1. Earth : Others are natural luminous bodies.

2. Glass : Others are opaque objects.

3. Mirror : It reflects light.

4. A plane mirror : Others are required for the formation of

shadow.

5. Reflection from mirror : Others are based on the principle of

rectilinear propagation of light.

E. DEFINE THE FOLLOWING TERMS

1. Luminous and nonluminous bodies.

Ans. 

The bodies which can emit light are called luminous bodies. The

sun, stars, burning candle, hot filament in an electric bulb are luminous

bodies.

The bodies which do not emit light are called nonluminous bodies.

For example : Tables, Chairs, the Earth, the Moon etc. are nonluminous

bodies.

2. Shadow.

Ans. A dark patch formed by obstruction of light by an opaque object

is called the shadow of that object.

3. Mirror.

Ans. A smooth and highly polished reflecting surface is called mirror.

4. Transparent material.

Ans. A material which allows light to pass through it is calledtransparent material.

5. Translucent material.

Ans. A material which allows only a part of light to pass through it iscalled a translucent material.

HIGHER ORDER THINKING SKILLS : Think and Answer

Q. 1. Is it possible to see through a sheet that does notpermit light to pass through it ? How is the material of such a sheet classified ?

Ans. No, it is not possible to see through such sheet which does not allow the light to pass through it. The material of such a sheet is classified as opaque.

Q. 2. Why don’t you see the image of your face when youstand in front of a clear glass window-pane ?

Ans. We cannot see the image of our face on a clear glass window pane because being transparent light passes through it instead of reflecting back.

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