Science (English Medium) Class 12 - CBSE Important Questions for Physics

Draw V-I characteristics of a p-n Junction diode.

Differentiate between the threshold voltage and the breakdown voltage for a diode.

Two crystals C₁ and C₂, made of pure silicon, are doped with arsenic and aluminium respectively.

Identify the extrinsic semiconductors so formed.

Two crystals C₁ and C₂, made of pure silicon, are doped with arsenic and aluminium respectively.

Why is doping of intrinsic semiconductors necessary?

Give two differences between a half-wave rectifier and a full-wave rectifier.

Briefly explain how emf is generated in a solar cell.

Draw solar cells of I-V characteristics.

Draw the circuit diagram of an illuminated photodiode and its I-V characteristics.

How can a photodiode be used to measure light intensity?

Draw the energy band diagrams for conductors, semiconductors and insulators. Which band determines the electrical conductivity of a solid? How is the electrical conductivity of a semiconductor affected with rise in its temperature? Explain.

Name the extrinsic semiconductors formed when pure germanium is doped with a trivalent impurity. Draw the energy band diagram of extrinsic semiconductors so formed.

Name the extrinsic semiconductors formed when pure germanium is doped with a Pentavalent impurity. Draw the energy band diagram of extrinsic semiconductors so formed.

A semiconductor device is connected in series with a battery, an ammeter and a resistor. A current flows in the circuit. If. the polarity of the battery is reversed, the current in the circuit almost becomes zero. The device is a/an ______.

With the help of a circuit diagram, explain how a full wave rectifier gives output rectified voltage corresponding to both halves of the input ac voltage.

• Assertion (A): The resistance of an intrinsic semiconductor decreases with an increase in its temperature.
• Reason (R): The number of conduction electrons as well as hole increase in an intrinsic semiconductor with the rise in its temperature.

• Assertion (A): In insulators, the forbidden gap is very large.
• Reason (R): The valence electrons in an atom of an insulator are very tightly bound to the nucleus.

The energy required by an electron to jump the forbidden band in silicon at room temperature is about ______.

Which one of the following elements will require the highest energy to take out an electron from them?

Pb, Ge, C and Si

• Assertion (A): Putting the p-type semiconductor slab directly in physical contact with the n-type semiconductor slab cannot form the pn junction.
• Reason (R): The roughness at contact will be much more than inter atomic crystal spacing and continuous flow of charge carriers is not possible.

Name the device which utilizes the unilateral action of a pn diode to convert ac into dc.