Important Questions and Answers: Solids and Semiconductor Devices

Solid and Semiconductors

1. Define conductor and semi-conductor on the basis of band theory.

Ans: The solid in which valance and conduction bands are overlapped to each other is called conductors. . Due to overlapping, even a slight potential difference across the conductor can cause the free electron to move and to generate current. There is very low resistance in semiconductor.

The solid in which width of forbidden band is small and the valance band is almost filled with electron while the conduction band is empty is called semiconductor.  The resistance of semiconductor is more than that of conductor.

2. Why is silicon preferred to germanium in manufacturing semiconductors?

Ans: Silicon is preferred to germanium in manufacturing semiconductors because of the following reasons:

  • Silicon has high temperature coefficient than germanium.
  • Silicon can operate at high temperature than germanium.
  • Silicon is comparatively cheaper.

3. What do you mean by hole in semi-conductor?

Ans: If an electron gets sufficient energy to jump from the valence band to the conduction band, the free electron moves from valence band to conduction band, the vacancy is left in the valance band. The vacancy left is called hole. It carries no charge but behaves like positive charge.

4. What is P-N junction diode ?

Ans: The device in which p-type semiconductor is in contact with n-type semiconductor is known as P-N Junction diode. It is also known as semiconductor diode or simple crystal diode.

P-N Junction Diode and its Representation

5. Why is semiconductor electrically neutral ?

Ans: A semiconductor contains equal number of electrons and holes in it. So,  it is electrically neutral.

6. How it is possible to rectify a.c.?

Ans: We know that a p-n junction act as a closed switch when it  is forward biased and as a open switch when it is reverse biased. This unidirectional property of the p-n junction makes possible to rectify a.c.

7. Why  is semiconductor damaged by a strong current?

Ans: When strong current is passed through a conductor, it heats up crystals and the covalent bonds are broken. Due to breaking of bonds,  semiconductor loses the property of low conductor creating large number of free electrons.

8. What is zener diode? What is its significance ?

Ans: A zener diode is an electronic component that allows the flow of current in only one direction. It is the properly crystal diode which works in reverse breakdown region. It is used to regulate voltage in electronic device.

9. What is filter circuit? Name the types of filter circuits.

Ans: The device which allows only DC components to reach the load by removing any AC component is known as filter circuit. A filter circuit is needed to get steady voltage with minimum ripple. The filter circuit consists of passive elements like inductor, capacitor and a resistor on their combination. There are four types of filter circuits.

  1. Capacitor filter circuit
  2. inductor filter circuit
  3. LC filter circuit
  4. Pi () filter circuit

10. What is logic gate? Explain its types.

Ans: A logic gate is an electric circuit which operates on one or more input signal to produce some specific output. The inputs and the outputs will be the logic value such as true/false, 1/0 etc. It is used for designing and developing IC, VLSI, Microprocessor, and different electronic circuits. Different logic gates used are:

  • AND Gate
  • OR gate
  • NOT gate
  • NAND gate
  • NOR gate
  • XOR gate
  • XNOR gate

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