30 important MCQs on the topic "Optics" for Class 12 students with answers and brief explanations below each answer:

 

Which of the following lights deviates the most when it passes through a prism?
a) Red Light
b) Violet Light
c) Neither (a) nor (b)
d) Both (a) and (b)
Answer: b) Violet Light
Explanation: Violet light has the shortest wavelength and hence suffers the greatest refraction and deviation.

When light travels from one medium to another, which of the following does not change?
a) Frequency
b) Refractive index
c) Velocity
d) Wavelength
Answer: a) Frequency
Explanation: Frequency remains constant when light passes from one medium to another.

For which of the following is the field of view maximum?
a) Concave mirror
b) Convex mirror
c) Plane mirror
d) Cylindrical mirror
Answer: b) Convex mirror
Explanation: Convex mirrors have a wider field of view which is why they are used as rearview mirrors.

Which of the following cannot be polarized?
a) Radiowaves
b) Transverse waves
c) Sound waves
d) X-rays
Answer: c) Sound waves
Explanation: Sound waves are longitudinal waves and cannot be polarized.

What happens when light is refracted into a denser medium?
a) Wavelength decreases but frequency remains the same
b) Both wavelength and frequency increase
c) Both wavelength and frequency decrease
d) Wavelength increases but frequency remains constant
Answer: a) Wavelength decreases but frequency remains the same
Explanation: Frequency stays constant but wavelength decreases when light enters a denser medium.

The phenomenon responsible for mirage is:
a) Reflection
b) Refraction
c) Total internal reflection
d) Diffraction
Answer: c) Total internal reflection
Explanation: Mirage occurs due to total internal reflection of light in layers of hot air.

The focal length of a convex lens dipped in a liquid of the same refractive index as the lens would be:
a) Zero
b) Infinite
c) Reduced
d) Unchanged
Answer: b) Infinite
Explanation: When lens and medium refractive indices are same, lens effect vanishes and focal length becomes infinite.

The ratio of sine of angle of incidence to sine of angle of refraction is called:
a) Refractive index
b) Critical angle
c) Angle of minimum deviation
d) None of these
Answer: a) Refractive index
Explanation: This ratio defines the refractive index according to Snell's law.

Light travels from denser to rarer medium during:
a) Refraction
b) Diffraction
c) Total internal reflection
d) Polarization
Answer: c) Total internal reflection
Explanation: Total internal reflection occurs only when light passes from a denser to a rarer medium.

The focal length of a lens depends on:
a) The power of the lens
b) The refractive index of the material
c) The shape of the lens
d) All of the above
Answer: d) All of the above
Explanation: Focal length is related to the lens's power, material refractive index, and curvature.

When white light passes through a prism, which color deviates the least?
a) Red
b) Green
c) Blue
d) Violet
Answer: a) Red
Explanation: Red light has the longest wavelength and deviates the least through a prism.

The power of a lens is measured in:
a) Diopters
b) Watts
c) Newtons
d) Meters
Answer: a) Diopters
Explanation: Power of a lens is the reciprocal of focal length in meters, measured in diopters.

A ray of light falls on a mirror normally. What are the angles of incidence and reflection?
a) 0°, 0°
b) 45°, 45°
c) 90°, 90°
d) 30°, 30°
Answer: a) 0°, 0°
Explanation: Normally incident light has zero angles of incidence and reflection.

A concave lens always produces an image that is:
a) Real and inverted
b) Virtual and erect
c) Real and erect
d) Virtual and inverted
Answer: b) Virtual and erect
Explanation: Concave lenses always form virtual, erect, and diminished images.

In Young’s double-slit experiment, fringe width on the screen increases by:
a) Increasing wavelength
b) Decreasing slit separation
c) Increasing distance between slits and screen
d) All of the above
Answer: d) All of the above
Explanation: Fringe width depends directly on wavelength and screen distance, inversely on slit separation.

When light passes from air to glass, its wavelength:
a) Increases
b) Decreases
c) Remains same
d) Becomes zero
Answer: b) Decreases
Explanation: Wavelength decreases in denser media as velocity decreases.

The critical angle for glass-air interface is approximately:
a) 30°
b) 42°
c) 60°
d) 90°
Answer: b) 42°
Explanation: Critical angle is where light undergoes total internal reflection.

The image formed by a plane mirror is always:
a) Real
b) Virtual
c) Enlarged
d) Inverted
Answer: b) Virtual
Explanation: Plane mirrors produce virtual, erect, and laterally inverted images.

Lenses with focal length 50 cm and 20 cm are placed in contact. The equivalent focal length is:
a) 14.3 cm
b) 70 cm
c) 100 cm
d) 30 cm
Answer: a) 14.3 cm
Explanation: 1f=1f1+1f2⇒f=14.3 cm\frac{1}{f} = \frac{1}{f_1} + \frac{1}{f_2} \Rightarrow f = 14.3 \text{ cm}f1=f11+f21⇒f=14.3 cm.

The image formed by a convex mirror is always:
a) Real and inverted
b) Virtual and erect
c) Real and erect
d) Virtual and inverted
Answer: b) Virtual and erect
Explanation: Convex mirrors form virtual, erect, and diminished images.

When light passes through a polarizer, the transmitted intensity is:
a) Equal to incident intensity
b) Half of incident intensity
c) Zero
d) Twice the incident intensity
Answer: b) Half of incident intensity
Explanation: Ideal polarizer transmits half the unpolarized light intensity.

The phenomenon of splitting of a beam of light into colors is called:
a) Diffraction
b) Dispersion
c) Interference
d) Polarization
Answer: b) Dispersion
Explanation: Dispersion separates white light into constituent colors by refraction.

The laws of refraction were discovered by:
a) Newton
b) Huygens
c) Snell
d) Maxwell
Answer: c) Snell
Explanation: Snell's law quantifies refraction angles for different media.

The refractive index of diamond is:
a) 1.33
b) 1.5
c) 2.42
d) 1.0
Answer: c) 2.42
Explanation: Diamond has a high refractive index making it sparkle intensely.

Total internal reflection occurs only if the angle of incidence is:
a) Less than critical angle
b) Equal to critical angle
c) Greater than critical angle
d) Zero
Answer: c) Greater than critical angle
Explanation: Total internal reflection happens only beyond the critical angle.

The focal length of a concave mirror is:
a) Negative
b) Positive
c) Zero
d) Infinite
Answer: a) Negative
Explanation: Focal length of a concave mirror is considered negative by sign convention.

The virtual image produced by a diverging lens is always:
a) Real
b) Smaller than the object
c) Larger than the object
d) Same size as object
Answer: b) Smaller than the object
Explanation: Diverging (concave) lenses produce smaller virtual images.

The phenomenon responsible for the blue color of the sky is:
a) Reflection
b) Scattering
c) Refraction
d) Dispersion
Answer: b) Scattering
Explanation: Rayleigh scattering of sunlight by air molecules causes the blue sky.

A telescope forms an image at infinity for relaxed eye when:
a) Object is at infinity
b) Object is at finite distance
c) Eyepiece is removed
d) Objective lens is removed
Answer: a) Object is at infinity
Explanation: Telescope is adjusted for infinity for comfortable viewing by relaxed eye.

Which optical instrument is used to produce a virtual, magnified image of small objects?
a) Microscope
b) Telescope
c) Spectrometer
d) Periscope
Answer: a) Microscope
Explanation: Microscope uses lenses to produce magnified virtual images of small objects.