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Red colour light has maximum wavelength, it does not scatter due to atmosphere and reaches our eyes, travels fast and hence used for danger signals.

The sun is visible to us 2 minutes before the actual sunrise because of atmospheric refraction. When the sun is below the horizon, the light travelling from rarer to denser medium bends and reaches our eyes creating an impression that it is above the horizon.

The molecules of air and other fine particles in the atmosphere have sizesmaller than the wavelength of the visible light. 

These are more effective in scattering light of shorter wavelength at the blue end than the light of a longer wavelength at the red end. Thus, the blue colouris due to the scattering of sunlight through fine particles in the air.

Clear sky appears blue because the white light of sun when enters the earth’s atmosphere the large number of molecules present in the earth’s atmosphere scatter the light. As blue light scatters the maximum it reaches our eyes.

Myopia is a defect in which the image is formed in front of retina. We need to use diverging lens so that it can further diverge the light rays before it enters our eye and make it possible to meet on the retina. 

In case of hypermetropia, the image is formed beyond retina, we need to use convex lens so as to converge the rays and make it possible for the rays to meets on the retina.

• Blue is the colour in visible spectrum which is having maximum scattering.
• This makes the blue colour to reach us and the sky appears blue.

Clear sky appears blue. 

Reason: When sunlight passes through the atmosphere having the molecules of air and other fine particles, whose size is smaller than the wavelength of visible light, these molecules and particles scatter the blue colour more strongly than the other colours of spectrum as the wavelength of blue colour is more. This scattered blue light enters our eye. So, the colour of sky appears blue to us during day time

Sky appears dark. 

Reason: In the absence of atmosphere, there would have been no scattering of sunlight at all.

The focal length of the eye lens will be more in case 

(a), i.e. when ciliary muscles of a normal eye is most relaxed. 

(b) Reason: When ciliary muscles are relaxed, the eye lens becomes thin. Thus, its focal length increases. In case when ciliary muscles is in most contracted state, radius of curvature of eye lens increases. Lens becomes thicker. This decreases the focal length of eye lens.

The near point of hypermetropic eye is shifted farther away from the normal near point.

C) beyond the retina

1. B. Fear

2. C. As her father hit on her palm with a ruler.

3. B. Kezia’s hatred for her father 

4. C. She tried to explain the things to Kezia’s father that Kezia had not done anything deliberately.

The rays coming from the face of person, sitting across the camp fire, suffer refraction on passing through hot air. Thus, we see apparent image of person. Since hot air is in motion, therefore its optical density changes, which in turn shifts the image rapidly. This rapidly shifting image gives a shimmering effect.

Yes, we can derive the relation between angle of incidence and angles of refraction theoretically. We can get nt sin i = n₂ sin r.

1. 90° 

2. Snell’s law 

3. 3 × 10⁸ m/s 

4. denser, rarer 

5. 2 × 10⁸ m/s 

6. optical illusion / total internal reflection.

(i) Refraction of light. (ii) Refraction of light.

1. (ii) Another thief lady is speaking to Horace Danby.

2. (ii) Yes, there is truth in what the lady said.

3. (iii) Yes, there is truth in what the lady said because she interrupted Horace's robbery and startled him.

4. (iv) The familiar way Sherry - the dog of the house, followed her, the confidence, the authoritative voice and the reason for opening the safe - all made her look like the real mistress of the house.

5. (i) The house was Shotover Grange.

Horace Danby liked to collect rare and expensive books.

Refractive index depends on (1) Nature of material and (2) Wavelength of light used.

₂n₁ = sin i, where i is the critical angle.

It is a phenomenon in which a ray of light deviates from its original path, while travelling from one optical medium to another optical medium. 

1. (i) Horace felt sure of his success because he had planned his work carefully.

2. (ii) He had been studying Shotover Grange because it was his next target to be burgled.

3. (iii) The servants were at the movies.

4. (iv) The owners had a dog.

5. (i) The owners had two servants.

A lady standing in the doorway was speaking to Horace Danby. She was young and pretty and was dressed in red. She said she had come just in time, or else her family would have been robbed by Horace. She, thus, pretended to be one of the members of the family living at Shot over Grange.

A) low refractive index

Formula:

₂n₁ = v₁/v₂, ₁n₂ = v₂/v₁

The change in the direction of propagation of light when it passes obliquely from one transparent medium to another is called refraction of light.

A) optic centre

1. (i) Horace had an allergy and suffered from fever. The pollen grains in the flowers made him sneeze again and again and were hindering him in his work.

2. (ii) Horace had gone there to rob a safe as there was no one in the house.

3. (iii) Horace is a thief.

4. (iv) The author is Victor Canning.

5. (ii) The extract is taken from 'A Question of Trust'.

The seagull was afraid of flying over the sea, because he thought that he would drown. His family decided to teach him a lesson. They left him unattended. The mother tore at a piece of fish that lay at her feet now and then in his front. Since the seagull was hungry too much, he was compelled to attempt his first flight in order to get food. He was successful. This is when he got over his fear flying over the sea.

Correct option is (B)water droplets

i. False. 

(In dispersion of white light by a glass prism, red colour is deviated the least.)

ii. True.

iii. True.

iv. True.

v. True.

vi. True.

[Note: The frequency of light remains the same in reflection and refraction.]

Mirage and twinkling of a star.

The velocity of light is different in different media. Hence, there is a change in the direction of propagation of light when it passes obliquely from one transparent medium to another.

i. (c) the speed of light changes

ii. (a) 1.5

iii. (a) light amplification by stimulated emission of radiation

iv. (b) diamond

v. (d) has no unit

Correct option is  B) Refraction

Correct option is  C) 4/6

1. d. The young seagull's father flew over him.

2. a. The young seagull was near the sea now.

3. b. The young seagull's two brothers and sister were flying around him curveting and banking and soaring and diving.

4. c. The young seagull commended himself to dive and soar and curve.

5. a. FALSE

Neutralization. It is associated with a chemical reaction between an acid and an alkali; others are phenomena associated with light.

i. (a) \(\frac{c}{n}\)

ii. (b) 2.4 × 10⁸ m/s

iii. (c) Violet

iv. (a) Red

v. (a) 50°

vi. (a) moves away from the slab

vii. (c) parallel to each other

viii. (b) the angle of deviation decreases but after certain value of incident angle, deviation angle increases

i. (c) refraction

ii. (c) passes unbent

iii. (a) 0°

iv. (a) 50°

v. (b) less than 30°

B) relative refractive index

The young seagull had two brothers and a sister. His parents flew with them to leave him alone on the ledge as he could not muster up the courage to fly with them. His parents could have fed him. But, they refused to give him any food. They wanted him to fly and dive for his food. They threatened to let him starve. They did so because they loved him.

The parents were right in what they did because they wanted to teach him the importance of confidence and self-reliance. One can’t depend on their parents all his life to be fed. Thus, it was important, for him to learn to fly dive and search his own food. So, the attitude the seagull family showed to him was actually their love, care and concern for him.

The woman in the control room was shocked when the writer asked about another aeroplane because there was no such plane flying in the sky that night as she saw on the radar.

i. Refractive index depends on the velocity of light. 

It is an experimental fact.

ii. The change in the direction of propagation of light rays while going from one medium to another is called refraction. This is definition of refraction. It is assumed that the ray of light passes obliquely from one medium to another.

1. b. The pilot could not .y over on either side of storm clouds because he had limited fuel, just enough to reach England by a straight route.

2. b. The pilot of the Dakota plane was flying from Paris to England.

3. c. The pilot did not go back to Paris because he was anxious to reach home.

4. c. Them' refers to the stormy clouds.

5. b. FALSE