Diffraction Grating

1) Define Diffraction?
Ans: The phenomenon of bending of light waves around the edges of obstacles and their spreading into the geometrical shadow of the obstacle is called diffraction of light.


2) Mention the two types of diffraction?
Ans: i) Fresnel diffraction
        ii)Fraunhofer diffraction


3) What is the type of diffraction in the diffraction grating experiment?
Ans: Fraunhofer diffraction is involved because the source and the screen are effectively at infinite distance.


4) What is grating?
Ans: A grating is a plane glass plate on which a large number of opaque rulings are drawn at equidistance with a diamond head.

Ultrasonic Interferometer

1) What are ultrasonic waves?
Ans: Ultrasonic waves are sound waves, whose frequencies are greater than 20KHz. Their wavelength is less than 1.65cm. They exhibit all the properties of sound waves and some additional properties.

2) What are the properties of ultrasonic waves?
Ans:
i)Ultrasonic waves are longitudinal waves of high frequency(greater than 20KHz). Owing to their short wave length they can travel long distances as a sharp beam.
ii) They undergo reflection and refraction.
iii) They produce heating effect, mechanical effect & chemical effect.
iv) They produce biological effect. Animals such as frogs and rats are killed when subjected to ultrasonic waves.


3) How are ultrasonic are produced?
Ans: Ultrasonic are produced by
i) Galton's whistle.
ii) Magnetostriction oscillator
iii) Piezo-electric generator

Galton'd whistle is primarily a mechanical device based on the principle of resonance of air column. It can produce ultrasonic waves about 30KHz.

A magnetostriction oscillator is based on the property of magnetostriction exhibited by ferromagnetic materials. It can produce ultrasonic waves of 25KHz.

Piezo-electic oscillator is also an electrical device, which makes use of the piezo-electric property of quartz. It generators ultrasonic waves of high frequencies.

Fermi Energy

1) What is meant by Fermi Energy and Fermi Level?

Ans: In a metal, the quantised energy levels are filled up by free electrons in accordance with Pauli's exclusive principle. The energy of the highest occupied level at absolute zero temperature is called the fermi energy and the corresponding energy level is known as the Fermi level.

2) What is meant by Fermi factor?

Ans: The probabilityof finding an electron having an particular value of energy E at a temperature T is given by Fermi-Dirac probability distribution function.

3) What is meant by thermionic emmision and thermionic work function?

Ans: The phenomenon of emission of electrons from a metal surface by supplying thermal energy to the metal is called thermionic emmision.

According to quantum free electron theory at absolute zero temperature energy levels EF are filled and the energy levels above EF are empty.With the increase of temperature, the electrons are thermally exicted and move to higher energy states. The minimum energy that an electron should posses in order to come out of  the surface of a metal is called thermionic work function.

Transistor Characteristics

1) What is transistor? what are the types of transistors?
Ans: Transistor is a three terminal semiconductor device.
 There are two types of semiconductor i.e,. n-p-n and p-n-p.

2) Define n-type and p-type semiconductors.
Ans: If an intrinsic semiconductoris doped with pentavalent impurity. Then it is called n-type semiconductors.
If it is doped with trivalent impurity then it is called p-type semiconductor.
 
3) What is doping?
Ans: Adding trivalent or pentavalent impurity to an intrinsic semiconductor is called doping.

4. What are three basic transistor connection modes? Which mode is most preferred? Why?
Ans: Common-Emitter, Common-Base & Common-Collector connections.
 CE mode is most preffered because CE modes gives Highest voltage gain.

5. Define current amplification factor of a transistor?
Ans: It is defined as ratio of change in collector current to change in base current.

7. What is the biasing rule of transistor?
Ans: Emitter base junction should be forward biased and collector base junction should be reversed biased.

8. What is semiconductor?
Ans: Semiconductor is a substancewhich has the resistivityin between that of conductor and insulator. semiconductor has negative temperature coefficient of resistance.

9) Which are the commonly used semiconductors?
Ans: Germanium & Silicon