The phenomenon of diffraction was discovered by ...... .

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)?

For the visibility of a diffraction pattern of a wave of light,the size of the slit or obstacle should be

For a parallel beam of monochromatic light of wavelength $\lambda$,diffraction is produced by a single slit whose width $a$ is of the order of the wavelength of the light. If $D$ is the distance of the screen from the slit,the width of the central maxima will be

$A$ slit of width $a$ is illuminated by red light of wavelength $6500 Å$. If the first diffraction minimum falls at $30^{\circ}$,then the value of $a$ is

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 ...... $\mathring A$.