Question

In the Davisson and Germer experiment, the tungsten filament is coated with:
A) Aluminum oxide
B) Barium chloride
C) Titanium oxide
D) Barium oxide.

Answer 1

Hint: The additional energy required by an electron to overcome the surface barrier of the metal is called the work function of the metal. It is the minimum energy required for an electron to just escape from the metal surface. Consider the work function of the given metals in the options to solve this question.

Complete step by step solution:
Barium oxide reduces the work function of the filament, which results in the ease ejection of electrons during thermionic emission, and hence the tungsten filament is coated with barium oxide.
At room temperature in metals, the electrons in the outer orbit of an atom are loosely bound to the nucleus and these are called “free electrons”. These electrons cannot leave the metal surface on their own. For that, we need to supply a certain amount of energy to the electrons to escape from the metal surface.

 $\therefore$ The correct option is (D).

Note:
This experiment proves the wave nature of matter. Clinton Davisson and Lester Germer performed an experiment where they let the filament beam fall on a nickel crystal, due to these electrons scattering which then is collected with help of a moving collector. This moving collector is connected with a galvanometer which shows the current production.
The experiment set up consists of:
- Evacuated chamber: so that electrons can move freely without air resistance.
- Electron gun: it comprises tungsten filament coated with barium oxide which is heated at low voltage, due to this it can be used to emit electrons.
- Battery: as high voltage supply used to accelerate electron
- Cylinder with a fine hole connected with a battery: this is connected to a battery to accelerate the electron and due to the hole in the cylinder sprays electrons in the form of a beam.
- Nickel target: electron beam falls on it and spreads.
- Movable detector: to detect the electron's intensity once it falls on nickel and spreads.
- Galvanometer: it is used to measure small current which is created when an electron hits the detector. The amount of current produced shows us the intensity of an electron in a particular area.