Question: 9 For Young’s double slit experiment, two statements are given below:
Statement I: If screen is moved away from the plane of slits, angular separation of the fringes remains constant.
Statement II : If the monochromatic source is replaced by another monochromatic source of larger wavelength, the angular separation of fringes decreases.
In the light of the above statements, choose the correct answer from the options given below:
(1) Statement I is true but Statement II is false.
(2) Statement I is false but Statement II is true.
(3) Both Statement I and Statement II are true.
(4) Both Statement I and Statement II are false.
Answer: Option (1)
Explanation:
In Young’s double slit experiment, the angular separation of fringes is given by
\theta=\frac{\lambda}{d},
where \lambda is the wavelength and d is the separation between the slits.
The angular separation does not depend on the distance of the screen from the slits.
Therefore, even if the screen is moved away, the angular separation of fringes remains constant.
Hence, Statement I is true.
If the monochromatic source is replaced by another source of larger wavelength,
the value of \lambda increases.
From \theta=\frac{\lambda}{d},
an increase in \lambda leads to an increase in angular separation, not a decrease.
Therefore, Statement II is false.
Hence, the correct answer is Option (1).