15 extra multiple-choice questions for Optics (10th Standard Science, Samacheer Kalvi), beyond the ones printed in the textbook — each with the correct option highlighted and a clear, worked explanation. Free to read in English and Tamil.
Q1
When a ray of light passes from a medium of refractive index 1.5 into a medium of refractive index 1.3, how does its speed and direction change?
- A. Its speed decreases and it bends towards the normal
- B. Its speed increases and it bends away from the normalCorrect
- C. Its speed decreases and it bends away from the normal
- D. Its speed increases and it bends towards the normal
Explanation. When light travels from a denser medium to a rarer medium, its speed increases because the refractive index of the second medium is lower. Consequently, the refracted ray bends away from the normal.
Q2
According to Rayleigh's scattering law, if the wavelength of light is reduced to half of its original value, by what factor will the amount of scattering change?
- A. It will decrease to 1/16 of its original value
- B. It will increase by a factor of 4
- C. It will increase by a factor of 16Correct
- D. It will decrease to 1/4 of its original value
Explanation. According to Rayleigh's law, scattering is inversely proportional to the fourth power of the wavelength. Reducing the wavelength by half increases the scattering by 2 to the power of 4, which is 16 times.
Q3
Which type of scattering is primarily responsible for the white appearance of clouds when sunlight falls on water droplets?
- A. Rayleigh scattering
- B. Mie scatteringCorrect
- C. Tyndall scattering
- D. Raman scattering
Explanation. Mie scattering occurs when the size of the scatterer is larger than or equal to the wavelength of light. It equally scatters all colors of light, making clouds appear white.
Q4
In Raman scattering, the scattered light contains additional spectral lines of frequencies other than the incident frequency. This phenomenon is observed when monochromatic light passes through which of the following?
- A. Only gases
- B. Only liquids
- C. Only transparent solids
- D. Gases, liquids, or transparent solidsCorrect
Explanation. Raman scattering occurs when monochromatic light passes through a gas, a liquid, or a transparent solid, resulting in scattered light with frequencies different from the incident light.
Q5
According to the Cartesian sign convention, which of the following distances is always taken as negative for spherical lenses?
- A. Focal length of a convex lens
- B. Distance of the object from the lensCorrect
- C. Distance of a real image formed behind the lens
- D. Height of an erect object placed above the principal axis
Explanation. Since the object is always placed on the left side of the lens, the object distance is measured against the direction of incident light, which is always negative according to the sign convention.
Q6
If the magnification produced by a spherical lens is -0.5, what is the nature and size of the image formed?
- A. Real, inverted and enlarged
- B. Real, inverted and diminishedCorrect
- C. Virtual, erect and enlarged
- D. Virtual, erect and diminished
Explanation. A negative magnification indicates that the image formed is real and inverted. An absolute value of magnification less than 1 indicates that the image is diminished in size.
Q7
Which part of the human eye acts as the main refracting surface where most of the refraction of entering light occurs?
- A. Iris
- B. Pupil
- C. CorneaCorrect
- D. Retina
Explanation. The cornea is the thin, transparent front layer of the eyeball and serves as the primary refracting surface for light entering the eye.
Q8
The power of accommodation of the human eye is achieved by changing the focal length of the eye lens. This is done with the help of which of the following?
- A. Optic nerves
- B. Ciliary musclesCorrect
- C. Iris muscles
- D. Sclera
Explanation. Ciliary muscles contract or relax to adjust the curvature and focal length of the flexible eye lens, allowing the eye to focus on both near and distant objects.
Q9
What is the maximum time interval between two consecutive light pulses below which the human eye cannot distinguish them separately?
- A. 1/10 second
- B. 1/16 secondCorrect
- C. 1/25 second
- D. 1/50 second
Explanation. The persistence of vision of the human eye is 1/16 of a second, meaning that any light pulses repeating faster than this interval will appear continuous.
Q10
A person suffering from myopia can see objects clearly only up to a distance of 5 meters. To see distant objects at infinity, what should be the focal length of the correcting lens?
- A. +5 meters
- B. -5 metersCorrect
- C. -2.5 meters
- D. +2.5 meters
Explanation. To correct myopia for seeing objects up to infinity, the required concave lens must have a focal length equal to negative of the person's far point, which is -5 meters.
Q11
An eye defect where a person cannot see parallel and horizontal lines clearly is called astigmatism. This defect can be corrected by using which type of lens?
- A. Bifocal lenses
- B. Cylindrical lensesCorrect
- C. Convex lenses
- D. Concave lenses
Explanation. Astigmatism, which is caused by imperfect structure of the refracting surfaces, is corrected by using cylindrical lenses.
Q12
A simple microscope consists of which of the following optical components?
- A. A concave lens of short focal length
- B. A convex lens of short focal lengthCorrect
- C. A concave lens of long focal length
- D. A convex lens of long focal length
Explanation. A simple microscope uses a single convex lens of short focal length to produce an erect, virtual, and magnified image of a tiny object.
Q13
In a compound microscope, how do the focal lengths of the objective lens and the eye lens compare?
- A. Objective lens has larger focal length, eye lens has shorter focal length
- B. Objective lens has shorter focal length, eye lens has larger focal lengthCorrect
- C. Both lenses have equal and short focal lengths
- D. Both lenses have equal and long focal lengths
Explanation. In a compound microscope, the objective lens has a shorter focal length to create a high linear magnification, while the eyepiece has a larger focal length.
Q14
If a lens has a focal length of -25 centimeters, what is its power?
- A. +4 D
- B. -4 DCorrect
- C. +0.04 D
- D. -0.04 D
Explanation. The power of a lens is the reciprocal of its focal length in meters. Since f is -0.25 meters, the power is 1 divided by -0.25, which equals -4 D.
Q15
When white light is refracted through a glass prism, why does a spectrum form?
- A. Because different colored lights travel with the same velocity in glass
- B. Because the refractive index of glass is different for different wavelengthsCorrect
- C. Because red light has the highest angle of refraction and violet has the smallest
- D. Because the prism reflects only certain colors of the white light
Explanation. A spectrum forms because different colors of light have different wavelengths, and the refractive index of glass depends on the wavelength. Thus, each color refracts at a different angle.
