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.
Assertion (A): A convex lens suffers from chromatic aberration.
Reason (R): All parallel rays of monochromatic light passing through a convex lens do not come to a focus at the same point.
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 single convex lens suffers from chromatic aberration due to dispersion, so (A) is true. For monochromatic light, ideal parallel rays passing through a convex lens *do* converge at a single focal point (ignoring spherical aberration). Hence, (R) is false.
Assertion (A): If an object moves in front of a concave mirror parallel to principal axis. The angle between the object velocity and image velocity can never be acute.
Reason (R): Object velocity and image velocity perpendicular to principal axis for spherical mirror is not same.
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
If an object moves along the principal axis, its image also moves along it, with velocities always anti-parallel (angle \(180^\circ\)), so (A) is true. Perpendicular components of velocity are related by \(v_{iy} = m v_{oy}\), where magnification \(m\) is generally not 1, so (R) is true. (R) does not explain (A).
Assertion (A): The Focal length of lens is same for all colours of light
Reason (R): The focal length depends only upon the material of the lens
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
The focal length of a lens is given by \(1/f = (n-1)(1/R_1 - 1/R_2)\). Since the refractive index \(n\) varies with the color of light, focal length is different for different colors. Thus (A) is false. Focal length depends on \(n\), \(R_1\), \(R_2\), and the surrounding medium, not only the material. Also, \(n\) for a material depends on color. So (R) is false. Both (A) and (R) are false.
Assertion (A): When light moves from a denser medium to rarer medium then Snell’s law can’t satisfied for all angle of incidence.
Reason (R): When light moves from denser to rarer medium, for angle of incidence greater than the critical angle, no refraction is possible.
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
Total internal reflection occurs when light travels from a denser to a rarer medium, and the angle of incidence (theta_i) is greater than the critical angle (theta_c). In this case, (sintheta_r) from Snell's law becomes greater than 1, implying no refraction is possible. Thus, Snell's law is not satisfied for all incidence angles, and the reason correctly explains this phenomenon.
Assertion (A): On hot summer days, optical density of different layer of air increases with height from ground.
Reason (R): Refractive index of air increases with its density.
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
On hot summer days, air near the ground is hotter and less dense. As height increases, air becomes cooler and denser. Since refractive index (and thus optical density) increases with density, the optical density of air layers increases with height. Therefore, both assertion and reason are true, and the reason explains the assertion.
Assertion (A): For observing a rainbow, sun should be shining in one part of the sky and it is raining in the opposite part of sky, and observer should stand with his back towards raining side.
Reason (R): Rainbow appears due to directly reflection of sunlight from water drops of rain.
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 rainbow, the sun must be behind the observer, and the rain in front. This means the observer's back should be towards the sun, not the raining side. Rainbow formation involves dispersion, total internal reflection, and refraction, not just direct reflection.