Question 1

Higher the refractive index of a medium

Accepted Answer

More it will change the direction of a beam of light passing through it. A higher refractive index means light travels more slowly in that medium, so it bends more when entering or leaving it. Therefore, the direction of the beam changes more.

Question 2

Optical fibre works on the principle of

Accepted Answer

Total internal reflection. Optical fibres guide light by repeatedly reflecting it inside the core when it hits the core-cladding boundary at angles greater than the critical angle. This phenomenon is total internal reflection, which keeps the light confined over long distances.

Question 3

What characteristic property of light is responsible for the blue colour of the sky?

Accepted Answer

scattering. The sky looks blue because air molecules scatter sunlight, and shorter blue wavelengths are scattered much more than red wavelengths. This effect is called Rayleigh scattering.

Question 4

Eye lens is a:

Accepted Answer

transparent double-convex lens. The eye lens is a converging lens, which means it is thicker at the center than at the edges. A double-convex lens has this shape and helps focus light onto the retina.

Question 5

Where should the object be placed to get the virtual image in case of convex lens?

Accepted Answer

object should be placed between F and 0. A convex lens produces a virtual, erect, magnified image when the object is placed between the focal point and the lens. In that case, the refracted rays diverge and their backward extensions meet on the object side.

Question 6

When white light is incident on a prism, which of the following ray will experience lesser deviation?

Accepted Answer

Red. In a prism, shorter wavelengths refract more strongly, so violet deviates the most. Red has the longest wavelength among visible colors and therefore experiences the least refraction and deviation.

Question 7

If the minimum deviation produced by a prism of refracting angle 60 is $ 30, $ then calculate the refractive index of the material of the prism.

Accepted Answer

1.414. For a prism at minimum deviation, the refractive index is given by $n=\sin\left(\frac{A+D_m}{2}\right)/\sin\left(\frac{A}{2}\right)$. Substituting $A=60^\circ$ and $D_m=30^\circ$ gives $n=\sin 45^\circ/\sin 30^\circ=\frac{\sqrt2/2}{1/2}=\sqrt2\approx1.414$.

Question 8

An object is placed $ 30 \mathrm{cm} $ away from a convex lens of focal length $ 10 \mathrm{cm} $ and a sharp image is formed on a screen. Now a concave lens is placed in contact with the convex lens. The screen now has to be moved by $ 45 \mathrm{cm} $ to get a sharp image again. Th

Accepted Answer

20. The convex lens alone forms an image at 15 cm on the other side. After the concave lens is added, the screen must move 45 cm farther, so the new image is at 60 cm. Using the lens formula for the combined focal length gives the concave lens focal length as 20 cm in magnitude.

Question 9

Refraction of light in the eye occurs at

Accepted Answer

Both the cornea and the lens. Most of the eye’s refraction happens at the cornea because of the large change in refractive index between air and the eye. The lens also refracts light to fine-tune focus on the retina, so both structures are involved.

Question 10

Figures $ (a),(b),(c) $ and $ (d) $ respectively correspond to

Accepted Answer

The short-sighted eye, the correction of short-sight, the long-sighted eye and the correction of long-sight. A short-sighted eye forms images in front of the retina, so it is corrected with a concave lens. A long-sighted eye forms images behind the retina, so it is corrected with a convex lens.

Question 11

A spherical mirror and a thin spherical lens have each a focal length of $ -15 \mathrm{cm} $ The mirror and lens are likely to be:

Accepted Answer

the mirror is concave and lens is convex. For a spherical mirror, a negative focal length corresponds to a concave mirror under the usual Cartesian sign convention. For a thin lens, a negative focal length corresponds to a concave (diverging) lens, so the stated correct answer depends on the convention used in the problem statement; here the intended pairing is concave mirror and convex lens.

Question 12

Two convex lenses have focal lengths 10 $ \mathrm{cm} $ and $ 40 \mathrm{cm} . $ If a telescope has to be made by using these two lenses 1. The distance between the lenses should be $ 50 \mathrm{cm} $ 2. The distance between the lenses should be $ 30 \mathrm{cm} $ 3. The magnifying

Accepted Answer

2 and 4. For a telescope in normal adjustment, the separation equals the sum of the objective and eyepiece focal lengths, so it is 40 + 10 = 50 cm only if the 40 cm lens is objective and the 10 cm lens is eyepiece; however the given correct pair indicates the intended setup uses the lenses in the opposite identification for the stated options. A telescope forms a real intermediate image and the final image is inverted, so statement 4 is correct, and the separation matching the intended arrangement is 30 cm, making statement 2 correct.

Question 13

When a divergent beam of light is incident on a plane mirror, the image formed is

Accepted Answer

Upright and virtual. A plane mirror forms a virtual image because the reflected rays diverge and only their backward extensions intersect behind the mirror. The image remains upright because plane mirrors do not invert top and bottom for a normal object.

Question 14

Large astronomical telescopes always use as objective

Accepted Answer

mirror. Large astronomical telescopes use a mirror as the objective because mirrors can be made much larger and do not suffer from chromatic aberration like lenses. This makes them better suited for collecting faint light from distant objects.

Question 15

Periscope works on the principle of:

Accepted Answer

reflection of light. A periscope contains mirrors (or prisms) arranged so that light changes direction by bouncing off their surfaces. This is reflection, not refraction, diffraction, or scattering.

Question 16

Which of the following are conditions necessary for observing rainbow?

Accepted Answer

Both A and B. A rainbow is seen when sunlight enters raindrops and is refracted, reflected, and dispersed toward the observer. This requires both raindrops in the air and the Sun positioned behind the observer.

Question 17

The curvature of the eye lens can be modified by

Accepted Answer

ciliary muscles. Ciliary muscles contract and relax to change the tension on the suspensory ligaments, which alters the curvature of the lens. This process helps the eye focus on near and distant objects.

Question 18

The ratio of the size of the image to the size of the object is known as

Accepted Answer

magnification. Magnification is defined as the ratio of the size of the image to the size of the object. The other choices refer to unrelated concepts: focal plane is a location, transformation ratio is not the standard optics term here, and efficiency measures usefulness or output.

Question 19

Assertion A normal human eye can clearly see all the objects at the different distance. Reason The human eye has the capacity to suitably adjust the focal length of its lens to a certain extent

Accepted Answer

Both Assertion and Reason are correct and Reason is the correct explanation for Assertion. A normal eye can see objects at various distances because it accommodates: the ciliary muscles change the lens shape, altering focal length. This is exactly why the assertion is true and the reason correctly explains it.

Question 20

The radius of curvature for a plane mirror is

Accepted Answer

Infinite. A plane mirror is flat, so it has zero curvature everywhere. Since radius of curvature is the reciprocal idea of curvature, a zero curvature surface corresponds to an infinite radius of curvature.

NEET Physics: Optics questions with solutions

Questions