Physics CH # 18


Definitions

1. Electronics

Electronics is a branch of Physics, which deals with the development of electron emitting devices, their utilization and controlling electron flow in electrical circuits designed for various purposes.

2. Semi Conductor

Substances whose electrical resistance lies between those of conductors and insulators are known as semi-conductors.

3. Doping

Mixing of any tetravalent element into a trivalent or pentavalent element so that its electrical conductivity increases is called dopping.

4. N-Type Substance
A pure semiconductor with a valency of three, doped with a pentavalent element is called n-type semiconductor.

5. P-Type Substance
A pure semiconductor with a valency of three doped with a trivalent element is called n-type semiconductor.

6. Diode

The common boundary of n-type and p-type regions in a semiconductor is called p-n junction diode. It allows the current to flow in only one direction.

7. Forward Biased
If the p-type material of a semi conductor diode is at a positive potential and the n-type material is at a negative potential then the diode is forward biased. It has a very low electrical resistance.

8. Reverse Biased
If the p-type material of a semi-conductor diode is at a negative potential and the n-type material is at a positive potential then the diode is reverse biased. It has a very high electrical resistance.

9. Rectification
The process of conversion of alternating current into direct current is known as rectification.

10. Rectifier
A rectifier is a device that converts Alternating current into Direct current.

11. Transistor
A transistor is a semiconductor, which consists of a thin central layer of one type of semiconductor material sandwiched between two relatively thick pieces of the other type of semiconductor. The central part is known as the base (b) and the pieces at either side are called the emitter (e) and the collector (c).


12. Npn Transistor

The npn transistor has a thin piece of p-type substance sandwiched between two pieces of n-type semiconductors.

13. Pnp Transistor
The pnp transistor has a thin piece of n-type substance sandwiched between two pieces of p-type semiconductors.

Radar:

Introduction:

Radar stands for Radio Detection and Ranging. It is used to detect and find out the distance of distant object with the help of radio waves.

Construction:

It consists of a transmitter, a receiver and several indicating devices.

Working:

1. Transmission: The transmitter generates very high frequency electromagnetic waves in the desired direction with the help of a concave antenna.

2. Receiving: These rays after striking an object are reflected back and are received by the radar antenna. The antenna feeds these rays in the indicating devices.

3. Processing: The indicating devices measure the time taken by the waves to return. They calculate the wave velocity and finally the distance of the object.
Radar waves can penetrate fog, clouds, haze and smoke.







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