$A$ light ray of wavelength $\lambda$ is passing through a pinhole of diameter $D$ and the effect is observed on a screen placed at a distance $L$ from the pinhole. The approximations of geometrical optics are applicable,if

Light of wavelength $\lambda$ is incident on a single slit of width $a$,and the distance between the slit and the screen is $D$. In the diffraction pattern,if the slit width is equal to the width of the central maximum,then $D=$

Define diffraction.

In an experiment, electrons are made to pass through a narrow slit of width '$d$' comparable to their de Broglie wavelength. They are detected on a screen at a distance '$D$' from the slit (see figure). Which of the following graphs can be expected to represent the number of electrons '$N$' detected as a function of the detector position '$y$' ($y = 0$ corresponds to the middle of the slit)?

The first diffraction minimum due to the single slit diffraction is seen at $\theta = 30^o$ for a light of wavelength $5000 \,\mathring{A}$ falling perpendicularly on the slit. The width of the slit is

The position of the direct image obtained at $O$,when a monochromatic beam of light is passed through a plane transmission grating at normal incidence,is shown in the figure. The diffracted images $A, B$,and $C$ correspond to the first,second,and third-order diffraction. When the source is replaced by another source of shorter wavelength,then: