Diffraction

A parallel beam of fast-moving electrons is incident normally on a narrow slit. A fluorescent screen is placed at a large distance from the slit. If the speed of the electrons is increased, which of the following statements is correct?

1.	The angular width of the central maximum of the diffraction pattern will increase.
2.	The angular width of the central maximum will decrease.
3.	The angular width of the central maximum will be unaffected.
4.	A diffraction pattern is not observed on the screen in the case of electrons.

At the first minimum adjacent to the central maximum of a single slit diffraction pattern, the phase difference between the Huygen’s wavelet from the edge of the slit and the wavelet from the midpoint of the slit is:

1.		2.
3.		4.

A linear aperture whose width is cm is placed immediately in front of a lens of focal length cm. The aperture is illuminated normally by a parallel beam of wavelength cm. The distance of the first dark band of the diffraction pattern from the centre of the screen is:

1.	cm	2.	cm
3.	cm	4.	cm

The ratio of resolving powers of an optical microscope for two wavelengths ${\mathrm{\backslash lambda}}_1$=4000 $\stackrel{0}{A}$ and ${\mathrm{\backslash lambda}}_2=6000$ $\stackrel{0}{A}$ is:

1. 9:4

2. 3:2

3. 16:81

4. 8:27