| Directions (Q. No. 1 to 7): In the following questions, A statement of Assertion is followed by a statement of Reason (R). Mark the correct choice as. |
| Assertion (A): According to Huygens theory no back-ward wavefront is possible. |
| Reason (R): Amplitude of secondary wavelets is proportional to\[\left( 1+\cos \theta \right)\], where \[\theta \] is the angle between the ray at the point of consideration and direction of secondary wavelet. |
A) Both A and R are true and R is the correct explanation of A
B) Both A and R are true but R is NOT the correct explanation of A
C) A is true but R is false
D) A is false and R is true
Correct Answer: A
Solution :
| Option [a] is correct |
| Explanation: According to Huygens theory each and every point on a wavefront is the source of secondary wavelets. Secondary wavelets do not proceed backward. So the assertion is true. |
| Kirchhoff's explained that amplitude of secondary wavelets is proportional to (1 + cos \[\theta \]), where 9 is the angle between the ray at the point of consideration and direction of secondary wavelets. In the backward direction \[\theta \] = \[{{180}^{o}}\]; so 1 + cos \[\theta \] = 0; so there secondary wavelets do not proceed backward. |
| Hence assertion and both are true and the reason properly explains the assertion. |
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