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): In medical technology endoscopy, optical fibres are used to facilitate visual examination of internal organs of the body.
Reason (R): Optical fibres are fabricated so that there should be very less absorption of light and hence no appreciable loss of light intensity.
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 fibers are indeed used in endoscopy to transmit light for internal examination. This is possible because they are designed for very low light absorption, ensuring minimal loss of light intensity over their length. Both statements are true and R explains A.
Assertion (A): In total internal reflection reflected light is in the phase with incident light.
Reason (R): Reflecting surface is rarer in TIR.
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
In Total Internal Reflection (TIR), light reflects from a denser medium into the same denser medium at the interface with a rarer medium. Reflection at a denser interface causes a \(\pi\) phase change, but in TIR, reflection from an 'optically denser medium-optically rarer medium' boundary results in no phase change in the reflected wave. Thus, (A) is true.
The reflecting surface in TIR is the interface between the denser and rarer media, not 'rarer'. Thus, (R) is false.
Therefore, (A) is true but (R) is false.
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): 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): Diamond in air shine brightly and when dipped in transparent oil, its shine reduces.
Reason (R): Diamond shines due to multiple total internal reflections.
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
Diamond's high refractive index leads to a small critical angle, causing multiple total internal reflections (TIR) and bright shine. When in oil, the refractive index difference with the surroundings decreases, increasing the critical angle, reducing TIR, and thus reducing its shine. Both (A) and (R) are true, and (R) explains (A).