XII.XV Communication Systems

Out of all the names who contributed in development of communication systems, one name that makes every Indian Student takes pride in is Sir Jagadish Chandra Bose. A crater on the moon has been named in his honour. Bose made his inventions public in order to allow others to further develop his research.

XII.XIV Semiconductor Electronics: Material, Devices And Simple Circuits

The energy band structure in solids may be classified in four broad types as shown in figure. The gap between the top of valence band and bottom of conduction band is called the energy gap.

In a pure semiconductor (intrinsic semiconductor), number of conduction electrons and holes is equal.

Semiconductor with an impurity doped into it is called extrinsic semiconductor

• n-type semiconductor (doped with pentavalent)
• p-type semiconductor (doped with trivalent)

The conductivity of a semiconductor increases as the temperature is increased, as more electrons cross the energy gap and number of electron holes pair increases.

XII.XIII Nuclei

Radioactivity is a nuclear phenomenon in which an unstable nucleus undergoes a decay:

• alpha decay in which a helium nucleus is emitted
• beta decay in which electrons or positrons are emitted
• gamma decay in which high energy photons are emitted

XII.XII Atoms

We did discuss about Thomson's Model of the Atom and Rutherford's model in Class IX. Go to this page if you want to read it again.

XII.X Wave Optics

XII.IX Ray Optics And Optical Instruments

XII.VIII Electromagnetic Waves

Maxwell's equation is a collection of four fundamental equations;

• Gauss' law of electricity
• Gauss' law of magnetism
• Faraday's law
• Ampere-Maxwell law