LIGHT – REFLECTION AND REFRACTION Rising Star Question and Answers

LIGHT – REFLECTION AND REFRACTION Rising Star Question and Answers

Answers

LEVEL–1: RISING STAR

4 Marks Questions

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1. Concave mirror – object at different positions

a) Object at infinity

• Image position: At focus F
• Size: Highly diminished / point-sized
• Nature: Real and inverted

b) Object between C and F

• Image position: Beyond C
• Size: Enlarged
• Nature: Real and inverted

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2. Concave mirror

a) Object beyond C

• Image position: Between C and F
• Size: Diminished
• Nature: Real and inverted

b) Object at C

• Image position: At C
• Size: Same size
• Nature: Real and inverted

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3. Bi-convex (convex) lens

a) Object at infinity

• Image position: At F₂
• Size: Highly diminished / point-sized
• Nature: Real and inverted

b) Object at F₁

• Image position: At infinity
• Size: Highly enlarged
• Nature: Real and inverted

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4. To obtain a virtual and erect image

Lens/Mirror	Position of object
Concave mirror	Between P and F
Convex mirror	Any position in front of the mirror
Concave lens	Any position in front of the lens
Convex lens	Between optical centre O and F₁

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5. Four applications of refraction in daily life

1. Spectacles for correcting vision.
2. Camera lenses for forming images.
3. Microscopes for magnifying tiny objects.
4. Telescopes for viewing distant objects.

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6. Correcting Hanok's misconceptions

Statement (i): “The light ray doesn't undergo any refraction during this experiment.”

Probing question:
➡️ When light passes obliquely from air into the glass slab, does its direction change at the first surface? Why?

Statement (ii): “The emergent ray always comes out in a different direction from the incident ray.”

Probing question:
➡️ When the incident ray and emergent ray are compared, are they parallel or do they have different directions? Under what condition can they be parallel?

Correct concept: In a rectangular glass slab, the emergent ray is generally parallel to the incident ray, but it is laterally displaced.

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7. Refractive index and speed of light

 

(iii) In which medium does light travel fastest?

Answer: Air

(iv) In which medium is the speed of light least?

The highest refractive index is Ruby (1.71).

Answer: Ruby

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8. Concave Mirror – Fill the Table

No.	Position of object	Position of image	Size	Nature
1	At infinity	At focus F	Highly diminished	Real and inverted
2	Beyond C	Between C and F	Diminished	Real and inverted
3	Between C and F	Beyond C	Enlarged	Real and inverted
4	Between P and F	Behind the mirror	Enlarged	Virtual and erect

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2 Marks Questions

1. Probing questions for Varun

Question 1: Does the speed of light remain the same when it travels from air into water or glass?

Question 2: What relationship exists between the refractive index of a medium and the speed of light in that medium?

Correct concept:

 n=c/v

So, the speed of light varies from one medium to another.

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2. Simple experiment to show refraction at home

Materials: Glass/tumbler, coin and water.

Procedure:

1. Place a coin at the bottom of a cup.
2. Move backward until the coin just disappears from view.
3. Without changing your position, ask someone to pour water into the cup.
4. The coin becomes visible again.

Conclusion: Light changes its direction when it passes from one medium to another. This phenomenon is called refraction of light.

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3. Why is a convex mirror preferred as a rear-view mirror?

A convex mirror:

• provides a wide field of view, and
• forms an erect and diminished image.

Therefore, the driver can see a larger area behind the vehicle.

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4. Two applications of concave mirrors

1. Shaving/makeup mirrors
2. Reflectors in vehicle headlights and torches

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5. Two applications of convex mirrors

1. Rear-view mirrors of vehicles
2. Security mirrors in shops, parking areas and roads

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6. World without lenses

Without lenses, many important devices would be affected, such as:

• Spectacles
• Cameras
• Microscopes
• Telescopes
• Projectors

Scientific observation, photography and correction of vision would become much more difficult.

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1 Mark Questions

1. Statement Analysis

Keerthi: Concave mirror will be used as a rear-view mirror. ❌

Vasu: Convex mirror will be used as a rear-view mirror. ✅

Answer:

Vasu's statement is correct

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2. A point on a lens through which a ray passes without deviation

Answer:

Optical Centre (O)

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3. Radius of curvature of a convex mirror

Given:

 f=16

Relation:

R=2f 

Therefore,

R=2(16)=32

Answer: 32 cm

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4. Power of a convex lens

Given:

f=50cm=0.50

Formula:

 P=1/f

P={1}/{0.50}=+2D 

Answer:

+2 D

Note: The power is positive because it is a convex (converging) lens.

LIGHT – REFLECTION AND REFRACTION Rising Star Question and Answers