Assertion (A): When white light passes successively through two identical prisms, one inverted with respect to other, then in emergent side, again white light is obtained.
Reason (R): Prism has no ability to create colour but it only separates the colours already present in white light.
1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (3) (A) is true but (R) is false
4. (4) Both (A) and (R) are false
View Answer
Assertion (A) is true; the second inverted prism recombines the dispersed light back into white light. Reason (R) is true; prisms only disperse existing colours, they do not create new ones. Reason (R) correctly explains Assertion (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): 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): A rectangular glass slab produces no deviation and no dispersion.
Reason (R): Dispersive power of glass slab is zero.
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
A rectangular glass slab causes no net angular deviation but does produce lateral shift. It causes dispersion for polychromatic light. So (A) is false. Glass, being a dispersive medium, has a non-zero dispersive power. So (R) is false. Thus, both (A) and (R) are false.
Assertion (A): A prism of refracting angle \(60^{\circ}\) is made of a material of refractive index \(\sqrt{2}\) for a certain wavelength. As light of this wavelength passes through the prism, the prism, angle of minimum deviation is \(30^{\circ}\).
Reason (R): At minimum deviation, angle of refraction of the first face is \(r_1 = A/2 = 30^{\circ}\).
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
For a prism at minimum deviation, the angle of refraction at the first face is \(r_1 = A/2\), where \(A\) is the prism angle. Given \(A = 60^{\circ}\), \(r_1 = 30^{\circ}\). This makes Reason (R) true. Using the prism formula \(n = \frac{sin((A + \delta_m)/2)}{sin(A/2)}\), with \(n=\sqrt{2}\) and \(A=60^{\circ}\), we find \(\delta_m = 30^{\circ}\). Thus, Assertion (A) is also true. Reason (R) provides a key condition used in calculating the minimum deviation, hence it is the correct explanation for (A).
Assertion (A): When a glass prism is immersed in water, the deviation caused by prism decrease.
Reason (R): Refractive index of glass prism relative to water is less than relative to air.
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
Deviation is given by (delta = (mu-1)A), where (mu), is the relative refractive index. When immersed in water, (mu_{gw} = mu_g/mu_w), which is less than (mu_{ga} = mu_g), (refractive index w.r.t. air). A smaller (mu), leads to a smaller deviation. Both assertion and reason are true, and R correctly explains A.
Assertion (A): Consider a prism A of refracting angle \(5^0\), and another prism B of refracting angle \(10^0\), . Both prisms are made of crown glass. If white light is incident on each prism, angular dispersion caused by prism B will be more.
Reason (R): Dispersive power depends on the nature material.
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
Angular dispersion is given by \(\delta = (\mu_v - \mu_r)A\), . Since both prisms are of the same material, \((\mu_v - \mu_r\),), is constant. Prism B has a larger angle (A), \((10^\circ\), vs \(5^\circ\),), so it will cause more angular dispersion, making A true. Dispersive power is indeed a property of the material, so R is true. However, R does not explain why prism B has more dispersion than A, which is due to its larger refracting angle.