Assertion (A): A convex lens of glass \((\mu = 1.5)\) behaves as a diverging lens when immersed in a medium of 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; if \(mu_{medium} > \mu_{lens}\), a convex lens becomes diverging due to sign change in the lens maker's formula. Reason R is true as it describes a typical concave (diverging) lens shape. But the shape of a diverging lens does not explain the behavioral change of a convex lens.
Assertion (A): The Snell’s law \(\mu sin \theta = \text{constant}\) is valid at different boundaries irrespective of the shape of the boundaries.
Reason (R): When light enters from vacuum into a medium of refractive index \(\mu\), its speed and wavelength increases by \(\mu\).
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
Snell's law is valid universally for light refraction. However, when light enters a medium of refractive index \(mu\) from vacuum, its speed and wavelength *decrease* by a factor of \(mu\), not increase. Thus, A is true, but R is false.
Assertion (A): A solid glass sphere is placed in air. A light ray enters into the sphere from outside. The ray cannot undergo total internal reflection inside the sphere.
Reason (R): The angle of incidence at \(\text{1}^ \ext{st}\) surface cannot be greater than the critical angle for air-glass system.
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
A light ray can undergo Total Internal Reflection (TIR) inside a glass sphere if the conditions are met at the glass-air interface. The reason incorrectly relates the critical angle to the first surface incidence and does not explain why TIR could not occur. Both A and R are false.
Assertion (A): Wavelength of light changes on changing medium.
Reason (R): Light ray always deviates from its path when refracted.
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
When light enters a new medium, its speed and wavelength change, while frequency remains constant. Light deviates upon refraction unless it strikes normally. Both A and R are true, but R describes a characteristic of refraction, not the cause of wavelength change.
Assertion (A): Turpentine is denser medium than water for light.
Reason (R): Unit volume of turpentine is heavier than unit volume of water.
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
Turpentine has a higher refractive index (optically denser) than water, so A is true. However, turpentine's mass density is less than water's, meaning a unit volume of turpentine is lighter than water. Therefore, R is false.
Assertion (A): Biconvex lens can form virtual image of a virtual object.
Reason (R): Nature of lens depends on refractive index of surrounding.
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
A biconvex lens can form a virtual image of a virtual object. The nature of a lens (converging/diverging) depends on the refractive index of the lens material relative to the surrounding medium. Therefore, both A and R are true, and R is the correct explanation of A.
Assertion (A): The minimum length of mirror required to form complete image of man of height \(H) is \(H/2\).
Reason (R): Image of an object is obtained if incident light ray reaches the reflecting surface.
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
The minimum length of a plane mirror to see a full image of a person of height \(H) is \(H/2\). Image formation occurs when light rays reach and reflect from a surface. Both statements are true, but R is a general principle and does not explain the specific \(H/2\) relation.
Assertion (A): Concave mirror can not form real image of real object.
Reason (R): Concave mirror behave as a diverging mirror.
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
A concave mirror is a converging mirror and can form real images of real objects when the object is beyond the focal point. Therefore, both Assertion (A) and Reason (R) are false.
Assertion (A): Radius of curvature of a concave mirror is \(20 \text{cm}\). If a real object is placed in front of a mirror at \(10 text{cm}\) from pole of the mirror, image is formed at infinity.
Reason (R): When object is placed at focus of a converging optical system then its image is formed at infinity.
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
For a concave mirror, \(R = 20 \text{cm}\), so \(f = R/2 = 10 \text{cm}\). An object placed at the focal point of a converging mirror forms its image at infinity. Both A and R are true, and R correctly explains A.
Assertion (A): The sun appears oval shape at sunrise.
Reason (R): At the time of sunrise sun appears a little before the actual sunrise.
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
Atmospheric refraction causes sunlight to bend as it passes through Earth's atmosphere. This phenomenon makes the sun appear to rise earlier and distorts its shape into an oval or flattened form at the horizon due to differential refraction. Both Assertion (A) and Reason (R) are true, and (R) provides a correct explanation for (A).