Class 9 General Science Chapter 9 Question Answer

Complete Notes of Class 9 General Science Chapter 9 Question Answer Basic Electronics Notes in 9th Class General Science Urdu Medium by Sir Usman Lateef Suib. These computerized notes are very helpful in the preparation of the Basic Electronics Notes for students of the Class 9 General Science Chapter 9 Question Answer these are according to the new paper patterns of all Punjab boards.

• Important Multiple Choice Questions (MCQs) and Short Questions of Chapter No.9: Basic Electronics in General Science 9th class Urdu Medium.
• 1. Semi-conductors, 2. Semi-conductor Diode, 3. Radiowaves, 4. Radio System, 5. Televison, 6. Satellite T. V.  7. Computer, 8. Analogue/Digital Converters, 9. Telecommunication, 10. Communication System
• Revolutionary changes have occurred in the world during the last fifty years. Specially, there has been much progress in the field of electronics. Early radio set was so big that two persons could hardly move it. People used to have huge gramophones to enjoy music. Conquest of space was confined to only imagination. In the beginning, big valves were used in the T.V. set. Computer occupied many rooms. 
• But today is the age of microchips. By the use of chips, T.V. and computers are reduced in size to such extent that they can be easily shifted from one place to another. Their efficiency has increased to many folds. Communication through satellites has become very common. Transmission from any place can be watched all over the world. This is all by virtue of electronics.
• "Electronics is the knowledge of behaviour and control of electric current".
• Electronics uses the electric current to convert information into signals. These signals could be of sound, picture, number or other informations.
• Semi-conductors: Electronic devices are used to control the electric current. Modern electronic devices mostly consist of semi- conductors. The major function of electronic devices is to amplify the week electric signals.
• Semi-conductor is such a substance which has the ability to conduct current in between conductors and insulators. Silicon and germanium are two common semi-conductors which belong to the fourth group of periodic table.
• In pure semi-conductors, no free electrons are available to conduct electric current at very low temperature but at ordinary temperature, some of the electrons get free. This makes it possible to conduct some current through the semi- conductor.
• Semi-conductors are made more useful by increasing their conductivity. This is done by adding some quantity of trivalent or pentavalent atoms as impurity while growing the cyrstals of silicon or germanium. This process is called doping. This addition is usually done in the ratio of one to 10^8 atoms.
• N-type Semi-conductor: When a pentavalent impurity such as arsenic (As) is added to silicon crystals, then due to this process the number of free electrons in the semi-conductor increases. Such a material is called as N-type semi-conductor. Most of the current flow through N-type semi-conductors is due to free electrons.
• P-type Semi-conductor: If a trivalent impurity such as aluminium (Al) is doped in silicon crystal, then there is a deficiency of an electron in the outermost orbit of silicon atom. This deficiency of electron is called a hole. Thus this type of doping increases the number of holes in the semi-conductor. Such material is known as P-type semi- conductor. The current flow through it is mostly due to the holes.
• Semi-conductor Diode: If the silicon crystal is doped in such a way that its one end becomes N-type and the other P-type then it is called a P-N junction diode or semi-conductor diode. The P part of diode is known as anode and N part as cathode.
• Forward Biased Diode: The symbol of diode. When the anode of a diode is connected to the positive terminal of the battery and the cathode to the negative terminal, the current starts flowing through the diode from p-type to n-type of the junction. This is known as forward biased diode.