JEE Advanced (Assertion-Reason Type): Ray & Wave Optics | Chapter-wise Tests for JEE Main & Advanced PDF Download

Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses.
Q.1. Assertion: When a light wave travels from a rarer to a denser medium, it loses speed. The reduction in speed imply a reduction in energy carried by the light wave.
Reason:  The energy of a wave is proportional to velocity of wave.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (d)
When a light wave travel from a rarer to a denser medium it loses speed, but energy carried by the wave does not depend on its speed. Instead, it depends on the amplitude of wave.

Q.2. Assertion: A narrow pulse of light is sent through a medium. The pulse will  retain its shape as it travels through the medium.
Reason: A narrow pulse is made of harmonic waves with a large range of wavelengths.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (e)
A narrow pulse is made of harmonic waves with a large range of wavelength. As speed of propagation is different for different wavelengths, the pulse cannot retain its shape while travelling through the medium.

Q.3. Assertion: No interference pattern is detected when two coherent sources are infinitely close to each other.
Reason: The fringe width is inversely proportional to the distance between the two slits.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (b)
When d is negligibly small, fringe width β which is proportional to 1/d may become too large. Even a single fringe may occupy the whole screen. Hence the pattern cannot be detected.

Q.4. Assertion: Newton's rings are formed in the reflected system. When the space between the lens and the glass plate is filled with a liquid of refractive index greater than that of glass, the central spot of the pattern is dark.
Reason: The reflection is Newton?s ring cases will be from a denser to a rarer medium and the two interfering rays are reflected under similar conditions.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (a)
The central spot of Newton's rings is dark when the medium between plano convex lens and plane glass is rarer than the medium of lens and glass. The central spot is dark because the phase change of π is introduced between the rays reflected from surfaces of denser to rarer and rarer to denser media.

Q.5. Assertion: The film which appears bright in reflected system will appear dark in the transmitted light and vice-versa.
Reason: The conditions for film to appear bright or dark in reflected light are just reverse to those in the transmitted light.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (a)
For reflected system of the film, the maxima or constructive interference is  while the maxima for transmitted system of film is given by equation 2μtcosr = nλ where t is thickness of the film and r is angle of reflection. From these two equations we can see that condition for maxima in reflected system and transmitted system are just opposite.

Q.6. Assertion: In Young's double slit experiment, the fringes become indistinct if one of the slits is covered with cellophane paper.
Reason: The cellophane paper decrease the wavelength of light.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (c)
 When one of slits is covered with cellophane paper, the intensity of light emerging from the slit is decreased (because this medium is translucent). Now the two interfering beam have different intensities or amplitudes. Hence intensity at minima will not be zero and fringes will become indistinct.

Q.7. Assertion: The unpolarised light and polarised light can be distinguished from each other by using polaroid.
Reason: A polaroid is capable of producing plane polarised beams of light.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (a)
When a polaroid is rotated in the path of unpolarised light, the intensity of light transmitted from polaroid remains undiminished (because unpolarised light contains waves vibrating in all possible planes with equal probability). However, when the polaroid is rotated in path of plane polarised light, its intensity will vary from maximum (when the vibrations of the plane polarised light are parallel to the axis of the polaroid) to minimum (when the direction of the vibrations becomes perpendicular to the axis of the crystal). Thus using polaroid we can easily verify that whether the light is polarised or not.

Q.8. Assertion: Nicol prism is used to produce and analyse plane polarised light.
Reason: Nicol prism reduces the intensity of light to zero.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (c)
 The nicol prism is made of calcite crystal. When light is passed through calcite crystal, it breaks up into two rays (i) the ordinary ray which has its electric vector perpendicular to the principal section of the crystal and (ii) the extra ordinary ray which has its electric vector parallel to the principal section.The nicol prism is made in such a way that it eliminates one of the two rays by total internal reflection, thus produces plane polarised light. It is generally found that the ordinary ray is eliminated and only the extra ordinary ray is transmitted through the prism. The nicol prism consists of two calcite crystal cut at ? 68° with its principal axis joined by a glue called Canada balsam.

Q.9. Assertion: In everyday life the Doppler's effect is observed readily for sound waves than light waves.
Reason: Velocity of light is greater than that of sound.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (b)
Doppler's effect is observed readily in sound wave due to larger wavelengths. The same is not the case with light due to shorter wavelength in everyday life.

Q.10. Assertion: In Youn's experiment, the fringe width for dark fringes is different from that for white fringes.
Reason: In Youn's double slit experiment the fringes are performed with a source of white light, then only black and bright fringes are observed.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (d)
 In Young' s experiments fringe width for dark and white fringes are same while in Young?s double slit experiment when a white light as a source is used, the central fringe is white around which few coloured fringes are observed on either side.

Q.11. Assertion: A red object appears dark in the yellow light
Reason: A red colour is scattered less.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (b)
 If both assertion and reason are true but reason is not the correct explanation of the assertion.

Q.12. Assertion: The stars twinkle while the planets do not.
Reason: The stars are much bigger in size than the planets.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (b)
The stars twinkle while the planets do not. It is due to variation in density of atmospheric layer. As the stars are very far and giving light continuously to us. So, the light coming from stars is found to change their intensity continuously. Hence they are seen twinkling. Also stars are much bigger in size than planets but it has nothing to deal with twinkling phenomenon

Q.13. Assertion: Owls can move freely during night.
Reason: They have large number of rods on their retina.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (c)
 Owls can move freely during night, because they have large number of cones on their retina which help them to see in night.

Q.14. Assertion: The air bubble shines in water.
Reason: Air bubble in water shines due to refraction of light

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (c)
Shining of air bubble in water is on account of total internal reflection.

Q.15. Assertion: In a movie, ordinarily 24 frames are projected per second from one end to the other of the complete film.
Reason: The image formed on retina of eye is sustained upto 1/10 second after the removal of stimulus.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (c)
After the removal of stimulus the image formed on retina is sustained up to 1/6 second.

Q.16. Assertion: Blue colour of sky appears due to scattering of blue colour.
Reason: Blue colour has shortest wave length in visible spectrum.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (a)
Because of smallest wavelength of blue colour it is scattered to large extent than other colours, so the sky appears blue.

Q.17. Assertion: Different colours travel with different speed in vacuum.
Reason: Wavelength of light depends on refractive index of medium.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (e)
The velocity of light of different colours (all wavelengths) is same in vacuum and

Q.18. Assertion: The colour of the green flower seen through red glass appears to be dark.
Reason: Red glass transmits only red light.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (a)
  The red glass absorbs the radiations emitted by green flowers; so flower appears black.

Q.19. Assertion: The fluorescent tube is considered better than an electric bulb.
Reason: Efficiency of fluorescent tube is more than the efficiency of electric bulb.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (a)
The efficiency of fluorescent tube is about 50 lumen/watt, whereas efficiency of electric bulb is about 12 lumen/watt. Thus for same amount of electric energy consumed, the tube gives nearly 4 times more light than the filament bulb.

Q.20. Assertion: The polar caps of earth are cold in comparison to equatorial plane.
Reason: The radiation absorbed by polar caps is less than the radiation absorbed by equatorial plane.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (c)
Polar caps receives almost the same amount of radiation as the equatorial plane. For the polar caps angle between sun rays and normal (to polar caps) tends to 90°. As per Lambert's cosine law, E ∝ cosθ, therefore E is zero. For the equatorial plane, q  = 0°, therefore E is maximum. Hence polar caps of earth are so cold. (where E is radiation received).