If work function of a metal is 4.2 eV, the cut off wavelength is

• 8000 A^o

• 7000 A^o

• 1472 A^o

• 2950 A^o

Why are infra-red waves often called heat waves? Explain.

What do you understand by the statement, 'Electromagnetic waves transport momentum'?

Wave property of electrons implies that they will show diffraction effects. Davisson and Germer demonstrated this by diffracting electrons from crystals. The law governing the diffraction from a crystal is obtained by requiring that electron waves reflected from the planes of atoms in a crystal interfere constructively (see in the figure).



If a strong diffraction peak is observed when electrons are incident at an angle ‘i’ from the normal to the crystal planes with distance’ between them (see figure), de Broglie wavelength λdB of electrons can be calculated by the relationship (n is an integer) 

Wave property of electrons implies that they will show diffraction effects. Davisson and Germer demonstrated this by diffracting electrons from crystals. The law governing the diffraction from a crystal is obtained by requiring that electron waves reflected from the planes of atoms in a crystal interfere constructively (see in the figure).



In an experiment, electrons are made to pass through a narrow slit of width’ 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 graph 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 time by a photoelectron to come out after the photon strikes is approximately

An alpha nucleus of energy 1 /2 mv² bombards a heavy nuclear target of charge Ze. Then the distance of closest approach for the alpha nucleus will be proportional to 

If I₀ is the intensity of the principal maximum in the single slit diffraction pattern, then what will be its intensity when the slit width is doubled?