Single Slit Diffraction

Q. The fraunhofer diffraction pattern of a single slit is formed at the focal plane of a lens of focal length $f$. The distance between $1^{st}$ and $2^{nd}$ maxima on screen is $y$ and $a$ is slit width. Then the wave length of light used is

1. $\frac{ay}{3f}$
2. $\frac{3f}{ya}$
3. $\frac{2f}{ay}$
4. $\frac{ay}{f}$

Q. The fraunhofer diffraction pattern of a single slit is formed at the focal plane of a lens of focal length $f$. The distance between $1^{st}$ and $2^{nd}$ maxima on screen is $y$ and $a$ is slit width. Then the wave length of light used is

1. $\frac{ay}{3f}$
2. $\frac{3f}{ya}$
3. $\frac{2f}{ay}$
4. $\frac{ay}{f}$

Q. Light of wavelength $\lambda$ is incident on a slit of width $d$. The resulting diffraction pattern is observed on a screen at a distance $D$. The linear width of the principal maxima is then equal to the width of the slit if $D$ equals

1. $\frac{d}{2\lambda }$
2. $\frac{3\lambda }{d}$
3. $\frac{d^2}{2\lambda }$
4. $\frac{2{\lambda }^2}{7d}$