Physics - Light & Optics Questions with Answers

Physics - Light & Optics questions with answers

10 sample questions from this topic with the correct option and the solution.

1. Q1. The blue colour of the sky appears due to:

   1. refraction of light by air molecules
   2. scattering of shorter wavelength of sunlight by air molecules
   3. absorption of blue light by air molecules
   4. reflection of light by air molecules

   Answer: (B) scattering of shorter wavelength of sunlight by air molecules

   Solution

   Sunlight contains all colours, and air molecules are much smaller than the wavelength of light. By Rayleigh scattering, shorter wavelengths such as blue are scattered far more strongly than longer wavelengths (scattering is proportional to 1/wavelength⁴). This scattered blue light reaches our eyes from all directions, so the sky looks blue. Hence the answer is scattering of shorter wavelength of sunlight by air molecules.

2. Q2. The capacity of the lens is defined as the inversion of its ________.

   1. Focal Length
   2. Radius of curvature
   3. Main axis
   4. Curvature

   Answer: (A) Focal Length

   Solution

   The power (capacity) of a lens is its ability to converge or diverge light. It is defined as the reciprocal (inverse) of its focal length, P = 1/f, with f in metres and power in dioptres. So the capacity of a lens is the inverse of its focal length.

3. Q3. The correct relation between v, u, and f for a spherical mirror is:

   1. 1 1 1 f + u = v
   2. 1 1 1 = − f v u
   3. 1 1 1 = + f u v
   4. v = u + f

   Answer: (C) 1 1 1 = + f u v

   Solution

   For a spherical mirror, the mirror formula relates the image distance v, object distance u and focal length f. It states that 1/f = 1/u + 1/v. This is the correct relation among the given choices.

4. Q4. The crystalline lens of the eye mainly helps in:

   1. Detecting colour of objects
   2. Sending signals to the brain
   3. Providing fine adjustment of focal length
   4. Controlling the amount of light entering the eye

   Answer: (C) Providing fine adjustment of focal length

   Solution

   In the eye, most of the bending of light occurs at the cornea. The crystalline lens changes its curvature with the help of ciliary muscles, which alters its focal length slightly. This fine adjustment lets the eye focus objects at different distances sharply on the retina. Hence it provides fine adjustment of focal length.

5. Q5. The defect of hypermetropia can be corrected by using which of the following?

   1. Cylindrical lens
   2. Prism
   3. Concave lens
   4. Convex lens

   Answer: (D) Convex lens

   Solution

   In hypermetropia (far-sightedness), the eye focuses the image of a near object behind the retina because the eyeball is too short or the lens is too weak. A convex lens converges the light rays before they enter the eye, so the image forms on the retina. Hence a convex lens corrects hypermetropia.

6. Q6. The defect in which a person cannot see distant objects clearly but can see nearby objects is called ___________.

   1. myopia
   2. hypermetropia
   3. astigmatism
   4. presbyopia

   Answer: (A) myopia

   Solution

   Myopia (short-sightedness) is the defect in which a person can see nearby objects clearly but cannot see distant objects clearly. The image of a distant object forms in front of the retina. It is corrected using a concave lens.

7. Q7. The danger signal lights are usually red in colour because red is:

   1. not scattered at all by fog or smoke
   2. highest reflected by fog or smoke
   3. least scattered by fog or smoke
   4. highest scattered by fog or smoke

   Answer: (C) least scattered by fog or smoke

   Solution

   Red light has the longest wavelength among visible colours. Since scattering is inversely proportional to the fourth power of wavelength, red is scattered the least by fog or smoke particles. So it travels farthest through them and remains visible from a distance, which is why danger signals are red.

8. Q8. The correct sign conventions for focal length (f) and radius of curvature (R) for the formation of images by spherical mirrors is:

   1. for convex mirror f is negative, R is negative
   2. for concave mirror f is negative, R is negative
   3. for convex mirror f is negative, R is positive
   4. for concave mirror f is positive, R is negative

   Answer: (B) for concave mirror f is negative, R is negative

   Solution

   By the new Cartesian sign convention, distances are measured from the pole, and those in the direction of the incident light are positive, while those opposite to it are negative. The centre of curvature and focus of a concave mirror lie in front of the mirror, against the direction of incident light, so both f and R are negative for a concave mirror. For a convex mirror both are positive.

9. Q9. The area of the retina where the vision is highest is-

   1. Vitreous body
   2. Blind spot
   3. Choroid
   4. Fovea

   Answer: (D) Fovea

   Solution

   The fovea is a small central depression in the macula of the retina. It is packed densely with cone cells and has almost no rods, which gives the sharpest and most detailed vision. The blind spot has no photoreceptors, while the vitreous body and choroid are not light-sensing regions.

10. Q10. The band of seven colours obtained on a screen due to dispersion is called _________.

    1. Shadow
    2. Spectrum
    3. Reflection pattern
    4. Image

    Answer: (B) Spectrum

    Solution

    When white light passes through a prism, it splits into its seven constituent colours (VIBGYOR). This phenomenon is called dispersion. The band of seven colours formed on a screen is called a spectrum.