Assertion (A): Blue colour of sky is due to scattering.
Reason (R): According to Rayleigh blue colour shows more scattering as compare to violet colour.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Assertion (A) is true, blue sky is a result of Rayleigh scattering. Reason (R) is false; Rayleigh scattering is inversely proportional to the fourth power of wavelength (\(1/lambda^4\)), meaning violet light (shorter wavelength) scatters more than blue light. Thus, A is true and R is false.
Assertion (A): A convex lens of glass \(\mu = 1.5\) behave as a diverging lens when immersed in carbon disulphide of higher refractive index \(\mu = 1.65\).
Reason (R): A diverging lens is thinner in the middle and thicker at the edges.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Assertion (A) is true; a lens acts as a diverging lens if the surrounding medium's refractive index is greater than the lens material's. Reason (R) is true; a concave lens (a common diverging lens) has this shape. R describes the shape of a diverging lens, not why a convex lens changes its behavior in a different medium. Thus, both are true, but R does not explain A.
Assertion (A): A ray of white light shows no dispersion on emerging from a glass slab although there occurs dispersion inside the glass slab.
Reason (R): The velocity of light inside the glass slab is same for all different colours.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Assertion (A) is true; due to the parallel surfaces of the glass slab, the dispersed colors recombine upon emerging, showing no net dispersion. Reason (R) is false; dispersion occurs precisely because the velocity of light (and thus refractive index) varies for different colors within the medium. Thus, A is true and R is false.
Assertion (A): A completely transparent material will be invisible in vacuum, when the refractive index is unity.
Reason (R): The ratio of the refractive index of red light to blue light in vacuum is less than unity.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Assertion (A) is true; if a material's refractive index matches the surrounding (vacuum, \(\mu=1\)), light passes through without deviation or reflection, making it invisible. Reason (R) is false; in vacuum, the refractive index is \(1\) for all colors, so their ratio is \(1\), not less than unity. Thus, A is true and R is false.
Assertion (A): For every observer rainbow is a personal one.
Reason (R): Every observer intercepts light from same water drops.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Assertion (A) is true; a rainbow's apparent position depends on the observer's location and the specific light rays from water droplets they intercept. Reason (R) is false; different observers see rainbows formed by light from *different* sets of water drops at different angles. Thus, A is true and R is false.
Assertion (A): The persistence of vision \(1/16\) second is used in cinematography.
Reason (R): The human eye forms the real image of an object at its retina.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Assertion (A) is true; the brain's retention of images for about \(1/16\) second creates motion from rapid stills. Reason (R) is true; the eye's lens system forms a real, inverted image on the retina. R describes a fundamental eye function, which is a prerequisite for A but not its direct explanation. Thus, both are true, but R does not explain A.
Assertion (A): Warning signals installed at the top of tall buildings and monuments employ red light.
Reason (R): Human eye is most sensitive to red colour.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Red light has the longest wavelength and scatters least, making it visible from a distance. Thus, (A) is true. However, the human eye is most sensitive to yellow-green light (approximately \(555\text{ nm}\)), not red. Thus, (R) is false. So, (A) is true but (R) is false.
Assertion (A): A single lens cannot be free from chromatic aberration.
Reason (R): When light passes through single lens dispersion must occur.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Chromatic aberration occurs because the refractive index of a lens material varies with wavelength (dispersion). A single lens always causes dispersion, leading to different focal points for different colors. Thus, both (A) and (R) are true, and (R) explains (A).
Assertion (A): When white light passes through a prism, deviation of violet light is more than green light.
Reason (R): In a prism average deviation is measured as deviation of yellow light.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Violet light has the highest refractive index in a prism, so it deviates most, hence (A) is true. Yellow light is generally used for average deviation calculations in dispersion, so (R) is true. However, (R) does not explain (A).
Assertion (A): Law of reflection is applicable for all type of mirrors.
Reason (R): Rays which are parallel to principal axis are known as paraxial rays.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Laws of reflection are fundamental and apply to all mirrors, so (A) is true. Paraxial rays are rays close and parallel to the principal axis, so (R) is true. (R) defines a term, it does not explain the universality of reflection laws.