Physics
Assertion (A): The stars twinkle while the planets do not.
Reason (R): Stars are more distant than the planets.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true and R is not the correct explanation of A.
- assertion is false but reason is true.
- assertion is true but reason is false.
Answer
1. Both A and R are true and R is the correct explanation of A.
Explanation
Assertion (A) is true. Planets do not twinkle because, unlike stars, they are seen as extended sources of light. When observing a planet, which appears as a disk rather than a point of light, the combined effect of a large number of point-sized sources averages out the total variation in the amount of light entering the observer's eye. This averaging effect nullifies the twinkling phenomenon, making planets appear steady in brightness.
Reason (R) is true. Planets are much closer to us than stars, so they are not point-sized objects to our eye. Hence, the fluctuations have a negligible effect and they don't seem to twinkle.
Related Questions
Assertion (A): A beam of white light gives a spectrum on passing through a hollow prism.
Reason (R): The speed of light outside the prism is same as the speed of light inside the prism.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true and R is not the correct explanation of A.
- assertion is false but reason is true.
- assertion is true but reason is false.
Assertion (A): If the angles of the base of a prism are equal, then in the position of minimum deviation, the refracted ray will pass parallely to the base of the prism.
Reason (R): For minimum deviation, angle of incidence is equal to the angle of emergence.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true and R is not the correct explanation of A.
- assertion is false but reason is true.
- assertion is true but reason is false.
Assertion (A): An empty test tube placed in water in a beaker with its mouth outside the water surface appears silvery when viewed from a suitable direction.
Reason (R): The substance in water appears silvery due to refraction of light.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true and R is not the correct explanation of A.
- assertion is false but reason is true.
- assertion is true but reason is false.
Assertion (A): Sound waves can travel in vacuum, but light waves cannot.
Reason (R): Light is an electromagnetic wave, but sound is a mechanical wave .
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true and R is not the correct explanation of A.
- assertion is false but reason is true.
- assertion is true but reason is false.