Light - Shadows and Reflections

 

D. Tick (✓) the odd-one out giving reason.

1.     Sun, Stars, Earth, Firefly (Jugnu)

Ans. Earth – others are luminous.

2.     Wood, Iron sheet, Glass, Rocks

Ans. Glass – transparent; others are opaque.

3.     Rock, Mirror, Iron plate, Plywood

Ans. Mirror – reflects light; others are opaque objects.

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

Ans. Plane mirror – not required for shadow formation.

5.     Solar eclipse, Pinhole camera, Rectilinear propagation of light, Reflection from mirror

Ans. Reflection from mirror – others relate to straight-line propagation of light.

E. Assertion-Reason

For question numbers 1 to 5, two statements are given—one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below : (a) Both Assertion and Reason are true and Reason is the correct explanation of the Assertion. (b) Both Assertion and Reason are true but Reason is not correct explanation of the Assertion. (c) Assertion is true but Reason is false. (d) Assertion is false but Reason is true.

1.     Assertion (A) : Moon is a luminous body.

Reason (R) : Moon reflects the light of the Sun falling on it.

Ans. (d) Assertion false, Reason true

2.     Assertion (A) : A shadow is formed when light is made to fall on an opaque object.

Reason (R) : Light travels in straight lines.

Ans. (b) Both true but reason not correct explanation

3.     Assertion (A) : The shadow is longer in the morning and evening and smaller in the noon.

4.     Reason (R) : If the light falls at a smaller angle, a longer shadow is formed.

Ans. (a) Both true and reason explains assertion

5.     Assertion (A) : An image is formed due to reflection of light.

Reason (R) : Image gives an idea about the colour, structure, etc. of an object.

Ans. (b) Both true but reason not correct explanation

6.     Assertion (A) : Light travels in a straight line.

Reason (R) : Light bounces off on falling on a smooth polished surface.

Ans. (b) Both true but reason not correct explanation

II. LOGIC-BASED QUESTIONS

Short and Long Answer

1.     In the given flow diagram, define X and Y with example. Behaviour of objects towards light X: These objects form a hazy shadow Y: These objects do not form any shadow Ans. Define X and Y

• X -> Translucent objects
• Example: frosted glass, butter paper

• Y -> Transparent objects
• Example: glass, water

2.     Complete the table given below.

Ans: 

3.     You are standing at a distance of 3 m from a plane mirror.

(a) What is the distance of your image from the mirror ?

Ans. Plane mirror distance Distance of image from mirror = 3 m behind mirror

(b) What is the distance between you and your image ?

Ans. Distance between person and image = 6 m

4.     Write down the English alphabet in which the image formed in a plane mirror appears exactly the same as the alphabet. Give reason.

Ans. Letters unchanged in mirror Examples: A, H, I, M, O, T, U, V, W, X, Y Reason: They have vertical symmetry, so they appear the same in a mirror.

5.     Can you 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 ?

Ans. Shape producing circular and rectangular shadows Example: Cylinder (like a tin can)

• From top -> circular shadow
• From side -> rectangular shadow

6.     A sheet of plywood, a piece of muslin cloth and that of a transparent glass, all of the same size and shape were placed at A one by one in the arrangement shown in Figure. Will the shadow be formed in each case. If yes, how will the shadow on the screen be different in each case ? Give reasons for your answer.

Ans. Shadow formation for different materials

Material: Plywood, Muslin cloth, Transparent glass

Shadow: Dark and clear shadow, Faint shadow, No shadow

Reason: Different materials allow different amounts of light to pass.

III. HIGHER ORDER THINKING SKILLS

1.     Is it possible to see through a sheet that does not permit light to pass through it ? How is the material of such a sheet classified ?

 Ans. No. Such a sheet is opaque.

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

Ans. Because glass is transparent, most light passes through instead of reflecting.

3.     Is air around us always transparent ?

Ans. No. Air becomes translucent when dust, smoke, or fog is present.

4.     Is the nature of a mirror luminous or nonluminous? Give reason.

Ans. Non-luminous. A mirror is non-luminous because it reflects light but does not emit its own light.