Human Eye and Colourful World Science - Human Eye and Colourful World

• A
  Dispersion of light by water droplets.
• ✓
  Refraction of light by different layers of varying refractive indices.
• C
  Scattering of light by dust particles.
• D
  Internal reflection of light by clouds.

Answer: B.

• A
  Is scattered the most by smoke or fog.
• ✓
  Is scattered the least by smoke or fog.
• C
  Is absorbed the most by smoke or fog.
• D
  Moves fastest in air.

Answer: B.

• A
  +0.5D
• ✓
  -0.5D
• C
  +0.2D
• D
  -0.2D

Answer: B.

• A
  Reflection, refraction and dispersion.
• B
  Refraction, dispersion and total internal reflection.
• ✓
  Refraction, dispersion and internal reflection.
• D
  Dispersion, scattering and total internal reflection.

Answer: C.

• ✓
  Are relaxed and lens becomes thinner.
• B
  Contract and lens becomes thicker.
• C
  Are relaxed and lens becomes thicker.
• D
  Contract and lens becomes thinner.

Answer: A.

• ✓
  1. She is suffering from myopia.
  2. $\text{f}=\frac{1}{\text{P}}=-\frac{1}{4.5}=-0.22\text{m}=-22\text{cm}.$
  3. Concave lens.

Answer: A.

• ✓
  No. Light emitted by distant stars (act as point sources of light) passes through the atmosphere of the earth before reaching our eyes. The atmosphere of the earth is not uniform but consists of many layers of different densities. The layers close to the surface of the earth are optically denser. As we go higher and higher, the density of layers and refractive index decreases progressively. As the light from a star enters the upper­most layer of the atmosphere, it bends towards the normal as it enters the next layer. This process continues till the light enters our eyes. So due to refraction of light, the apparent position of the star is different from the actual position of the star (Figure).
  

Answer: A.

• ✓
  
  

Answer: A.

• ✓
  For this, one prism is placed near another prism so that one prism is in erect position and another prism is in inverted position. When ray of white light enters the first prism, dispersion of light takes place. When lights of different colours pass through the second prism, they recombine to make a ray of white light.

Answer: A.

• ✓
  Human eyes have power of accommodation. When we have to see distant objects, the eye muscles relax and lens becomes thin. Due to this, the focal length of the lens increases and the eye is able to see distant objects. When we have to see nearby objects, the eye muscles contract and lens becomes thick. Due to this, the focal length of the lens decreases and the eye is able to see nearby objects.

Answer: A.

• ✓
  When sunlight enters the earth’s atmosphere, the atoms or molecules of the gases present in the atmosphere scatter this light. Since wavelength of red colour is larger than the wavelengths of other colours in sunlight, so red colour is scattered least. Violet colour is scattered the most followed by blue, green, yellow, orange and red colours respectively. Our eye is more sensitive to the blue light than the violet light. Therefore, scattered light in the sky contains blue colour in plenty and hence the clear sky appears blue.
  Note: Sky appears greyish over cities having industrial units. The smoke and dust particles in the atmosphere over such cities scatter red, orange and yellow colours more than other colours of small wavelengths. Hence, the sky appears greyish.
  

Answer: A.

• ✓
  No. Light emitted by distant stars (act as point sources of light) passes through the atmosphere of the earth before reaching our eyes. The atmosphere of the earth is not uniform but consists of many layers of different densities. The layers close to the surface of the earth are optically denser. As we go higher and higher, the density of layers and refractive index decreases progressively. As the light from a star enters the upper­most layer of the atmosphere, it bends towards the normal as it enters the next layer. This process continues till the light enters our eyes. So due to refraction of light, the apparent position of the star is different from the actual position of the star (Figure).
  
  

Answer: A.

• ✓
  For this, one prism is placed near another prism so that one prism is in erect position and another prism is in inverted position. When ray of white light enters the first prism, dispersion of light takes place. When lights of different colours pass through the second prism, they recombine to make a ray of white light.

  

Answer: A.

• ✓
  Human eyes have power of accommodation. When we have to see distant objects, the eye muscles relax and lens becomes thin. Due to this, the focal length of the lens increases and the eye is able to see distant objects. When we have to see nearby objects, the eye muscles contract and lens becomes thick. Due to this, the focal length of the lens decreases and the eye is able to see nearby objects.
  

Answer: A.

• ✓
  
  

  The light ray PE enters from air to glass (rarer to denser medium) at surface AB and therefore, bends towards the normal. The refracted ray EF now exits from glass and enters air (from denser to rarer medium) and therefore, bends away from the normal. Extrapolation of incident and emergent ray gives the angle of deviation.

Answer: A.