Science (English Medium) Class 12 - CBSE Question Bank Solutions for Physics

A current of 0.8 A flows in a conductor of 40 Ω for 1 minute. The heat produced in the conductor will be ______.

Answer the following giving reasons:

Impurities are added to intrinsic semiconductors.

• 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.

An ideal inductor is connected across an AC source of voltage. The current in the circuit ______.

What is the ratio of inductive and capacitive reactance in an ac circuit?

In a coil of resistance 100 Ω a current is induced by changing the magnetic flux through it. The variation of current with time is shown in the figure. The magnitude of change in flux through the coil is ______.

Using Huygens’s construction of secondary wavelets draw a diagram showing the passage of a plane wavefront from a denser to a rarer medium. Using it verifies Snell’s law.

Define the term drift velocity.

Derive an expression for  drift velocity of free electrons.

What is its relation with relaxation time?

Write its (‘mobility’ of charge carriers) S.I. unit

Distinguish between 'intrinsic' and 'extrinsic' semiconductors

Estimate the average drift speed of conduction electrons in a copper wire of cross-sectional area 2.5 × 10⁻⁷ m² carrying a current of 1.8 A. Assume the density of conduction electrons to be 9 × 10²⁸ m⁻³.

Estimate the average drift speed of conduction electrons in a copper wire of cross-sectional area 1.0 × 10⁻⁷ m² carrying a current of 1.5 A. Assume the density of conduction electrons to be 9 × 10²⁸ m⁻³

Estimate the average drift speed of conduction electrons in a copper wire of cross-sectional area 2·5 × 10⁻⁷ m² carrying a current of 2·7 A. Assume the density of conduction electrons to be 9 × 10²⁸ m⁻³

Two charges 5 × 10⁻⁸ C and −3 × 10⁻⁸ C are located 16 cm apart. At what point(s) on the line joining the two charges is the electric potential zero? Take the potential at infinity to be zero.

The number density of free electrons in a copper conductor is 8.5 × 10²⁸ m⁻³. How long does an electron take to drift from one end of a wire 3.0 m long to its other end? The area of cross-section of the wire is 2.0 × 10⁻⁶ m² and it is carrying a current of 3.0 A.

In a p-type semiconductos, which of the following statement is true:

The number of silicon atoms per m³ is 5 × 10²⁸. This is doped simultaneously with 5 × 10²² atoms per m³ of Arsenic and 5 × 10²⁰ per m³ atoms of Indium. Calculate the number of electrons and holes. Given that n_i= 1.5 × 10¹⁶ m⁻³. Is the material n-type or p-type?

How does drift velocity of electrons in a metallic conductor vary with increase in temperature? Explain.