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.
Assertion (A): If an object is placed between (f) and (2f) of a convex lens, a real image can be seen on a screen placed at image location. If the screen is removed then image will not be seen.
Reason (R): Real image of a object can not formed in 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
A real image is formed by the actual intersection of light rays and exists in space independently of a screen. It can be viewed by the eye even without a screen. Real images are formed in the medium where rays converge, typically air. Therefore, both assertion and reason are false.
Assertion (A): Optical fibre communication is fastest way of communication.
Reason (R): Optical interference between fibres 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
Optical fiber communication offers very high bandwidth and speed due to light's high frequency and minimal signal loss via total internal reflection. The design ensures minimal to effectively zero optical interference between fibers, which is crucial for maintaining signal integrity and enabling high data rates. Thus, both A and R are true, and R explains A.
Assertion (A): The formula \(\frac{1}{v} + \frac{1}{u} = \frac{1}{f}\) connecting u and v for a spherical mirror is valid only for mirrors whose sizes are very small compared to their radii of curvatures.
Reason (R): Laws of reflection are strictly valid for smaller size of optical system.
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
Mirror formula \(\frac{1}{v} + \frac{1}{u} = \frac{1}{f}\) is valid under paraxial approximation, which requires small aperture mirrors. Laws of reflection are fundamental, and their simplified application in the mirror formula relies on paraxial rays. Thus, both (A) and (R) are true, and (R) correctly explains (A).
Assertion (A): A point object is placed at a distance of \(26 \text{ cm}\) from a convex mirror of focal length \(26 \text{ cm}\). The image will form at infinity.
Reason (R): For above given system the equation \(\frac{1}{v} – \frac{1}{u} = \frac{1}{f}\) gives position of image.
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 convex mirror, focal length \(f = +26 \text{ cm}\). Object distance \(u = -26 \text{ cm}\). Using mirror formula \(\frac{1}{v} + \frac{1}{u} = \frac{1}{f}\) gives \(\frac{1}{v} = \frac{1}{26} - \frac{1}{-26} = \frac{2}{26} = \frac{1}{13}\) so \(v = 13 \text{ cm}\). (A) is false. The correct mirror formula is \(\frac{1}{v} + \frac{1}{u} = \frac{1}{f}\) not \(\frac{1}{v} - \frac{1}{u} = \frac{1}{f}\). (R) is false. Thus, both (A) and (R) are false.