20 Optical Instruments Quiz Questions and Answers

Question 1:
What is the primary function of a convex lens in optical instruments?
A) To diverge light rays
B) To converge light rays
C) To reflect light rays
D) To absorb light rays
Answer: B
Explanation: A convex lens converges parallel light rays to a focal point, which is essential for forming real images in instruments like cameras and magnifiers.

Question 2:
In a compound microscope, which lens provides the initial magnification?
A) Eyepiece lens
B) Objective lens
C) Condenser lens
D) Projector lens
Answer: B
Explanation: The objective lens is closest to the specimen and produces a magnified real image, which is then further enlarged by the eyepiece.

Question 3:
What type of telescope uses a concave mirror as its primary optical element?
A) Refracting telescope
B) Reflecting telescope
C) Galilean telescope
D) Chromatic telescope
Answer: B
Explanation: Reflecting telescopes, like Newtonian ones, use a concave mirror to collect and focus light, reducing chromatic aberration compared to refracting telescopes.

Question 4:
Which optical instrument is used to measure the refractive index of a material?
A) Spectrometer
B) Microscope
C) Periscope
D) Binoculars
Answer: A
Explanation: A spectrometer analyzes the spectrum of light to determine properties like the refractive index by measuring how light bends through the material.

Question 5:
What is the role of the aperture in a camera?
A) To focus the image
B) To control the amount of light entering
C) To magnify the subject
D) To store the image
Answer: B
Explanation: The aperture adjusts the size of the lens opening, controlling light exposure and depth of field in photography.

Question 6:
In fiber optics, what principle allows light to travel through the fiber?
A) Reflection
B) Refraction
C) Total internal reflection
D) Diffraction
Answer: C
Explanation: Total internal reflection occurs when light hits the fiber’s boundary at an angle greater than the critical angle, allowing it to propagate along the fiber with minimal loss.

Question 7:
Which lens is used in a simple magnifying glass?
A) Concave lens
B) Convex lens
C) Plano-convex lens
D) Double-concave lens
Answer: B
Explanation: A convex lens bends light rays to converge, creating a virtual, enlarged image when an object is placed within its focal length.

Question 8:
What corrects myopia in eyeglasses?
A) Convex lenses
B) Concave lenses
C) Cylindrical lenses
D) Bifocal lenses
Answer: B
Explanation: Concave lenses diverge light rays, helping to focus the image on the retina for nearsighted individuals by counteracting the eye’s excessive convergence.

Question 9:
In a prism spectrometer, what does the prism do?
A) Amplify light
B) Disperse light into its spectrum
C) Reflect light directly
D) Absorb ultraviolet light
Answer: B
Explanation: A prism refracts light at different angles based on wavelength, separating it into a spectrum for analysis of light sources.

Question 10:
What is the function of the eyepiece in a telescope?
A) To gather light from distant objects
B) To magnify the image formed by the objective
C) To stabilize the telescope
D) To filter out colors
Answer: B
Explanation: The eyepiece acts as a magnifying lens, enlarging the real image produced by the objective lens for the observer.

Question 11:
Which optical instrument uses a combination of lenses and mirrors to view objects around corners?
A) Microscope
B) Periscope
C) Telescope
D) Spectrometer
Answer: B
Explanation: A periscope uses mirrors or prisms at 45-degree angles to reflect light, allowing users to see over obstacles or around corners.

Question 12:
What type of mirror is used in a reflecting telescope’s primary mirror?
A) Plane mirror
B) Convex mirror
C) Concave mirror
D) Parabolic mirror
Answer: D
Explanation: A parabolic mirror is used to focus incoming parallel rays to a single point, minimizing spherical aberration in telescopes.

Question 13:
In photography, what does the shutter speed control?
A) The color of the image
B) The duration of light exposure
C) The lens focus
D) The image size
Answer: B
Explanation: Shutter speed determines how long the camera’s sensor is exposed to light, affecting motion blur and overall brightness.

Question 14:
What is the purpose of a Nicol prism in polarimeters?
A) To produce polarized light
B) To magnify small objects
C) To reflect infrared light
D) To disperse white light
Answer: A
Explanation: A Nicol prism polarizes light by allowing only one vibration direction to pass, which is used to measure the rotation of polarized light in solutions.

Question 15:
Which optical instrument is essential for viewing microorganisms?
A) Telescope
B) Microscope
C) Binoculars
D) Camera
Answer: B
Explanation: A microscope uses lenses to magnify tiny objects, allowing detailed observation of microorganisms that are invisible to the naked eye.

Question 16:
What causes chromatic aberration in lenses?
A) Uneven reflection
B) Different wavelengths refracting at different angles
C) Light absorption
D) Lens scratching
Answer: B
Explanation: Chromatic aberration occurs because shorter wavelengths (like blue light) bend more than longer ones (like red light) in a lens, causing color fringing.

Question 17:
In a camera obscura, how is an image formed?
A) By digital sensors
B) By light passing through a small hole and projecting an inverted image
C) By mirrors only
D) By laser beams
Answer: B
Explanation: A camera obscura uses a pinhole to allow light to enter and form an inverted real image on a surface inside the darkened box.

Question 18:
What is the key advantage of a zoom lens over a fixed focal length lens?
A) It is lighter
B) It allows variable magnification without changing lenses
C) It produces only black and white images
D) It requires less light
Answer: B
Explanation: A zoom lens changes its focal length, enabling different magnifications while keeping the camera focused, which is useful in varying shooting conditions.

Question 19:
Which part of the human eye acts like the aperture in a camera?
A) Retina
B) Iris
C) Lens
D) Cornea
Answer: B
Explanation: The iris controls the size of the pupil, regulating the amount of light entering the eye, similar to a camera’s aperture.

Question 20:
What principle explains how a diffraction grating separates light?
A) Reflection
B) Interference and diffraction of light waves
C) Total internal reflection
D) Refraction only
Answer: B
Explanation: A diffraction grating uses the wave nature of light, where interference from closely spaced slits creates a spectrum by diffracting light at different angles for each wavelength.