Light appears to travel in straight lines since

$A$ slit of width $a$ is illuminated by light of wavelength $\lambda$. The linear separation between $1^{st}$ and $3^{rd}$ minima in the diffraction pattern produced on a screen placed at a distance $D$ from the slit system is . . . . . . .

For Bragg's diffraction by a crystal to occur,the $X$-ray of wavelength $\lambda$ and interatomic distance $d$ must satisfy which condition?

Red light of wavelength $5400 \ \mathring{A}$ from a distant source falls on a slit $0.80 \ mm$ wide. Calculate the distance between the first two dark bands on each side of the central bright band in the diffraction pattern observed on a screen placed $1.4 \ m$ from the slit. (in $mm$)

The angular width of the central maxima in the Fraunhofer diffraction pattern of a slit is measured. The slit is illuminated by light of wavelength $6000 \ \mathring A$. When the slit is illuminated by light of another wavelength,the angular width decreases by $30\%$. The wavelength of this light will be ...... $\mathring A$.

$A$ parallel beam of monochromatic light falls normally on a single narrow slit. The angular width of the central maximum in the resulting diffraction pattern