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

Mention the two characteristic properties of the material suitable for making core of a transformer.

State the underlying principle of a transformer. How is the large scale transmission of electric energy over long distances done with the use of transformers?

 Identify the equivalent gate for the following circuit and write its truth table.

A magnetic needle, free to rotate in a vertical plane, orients itself vertically at a certain place on the Earth. What are the values of (i) Horizontal component of Earth’s magnetic field and (ii) angle of dip at this place?

Name the electromagnetic waves which (i) maintain the Earth’s warmth and (ii) are used in aircraft navigation.

Define dipole moment of an electric dipole. Is it a scalar or a vector?

Calculate the quality factor of a series LCR circuit with L = 2.0 H, C = 2μF and R = 10 Ω. Mention the significance of quality factor in LCR circuit.

A conducting rod held horizontally along East- West direction is dropped from rest from a certain height near the Earth’s surface. Why should there be an induced emf across the end of the rod? Draw a plot showing the instantaneous variation of emf as a function of time from the instant it begins to fall.

State the principle of a step-up transformer. Explain, with the help of a labeled diagram, its working ?

Describe briefly and two energy losses, giving the reasons for their occurrence in actual transformers ?

What is the angle of dip at a place where the horizontal and vertical components of the Earth’s magnetic field are equal?

Calculate the quality factor of a series LCR circuit with L = 4.0 H, C = 1, μF and R = 20 Ω.

Mention the significance of quality factor in LCR circuit.

Define electric dipole moment. 

Where on the surface of Earth is the angle of dip zero?

State the principle of working of a transformer. Can a transformer be used to step up or step down a d.c. voltage? Justify your answer.

Draw a labeled diagram of a full wave rectifier circuit. State its working principle. Show the input-output waveforms ?

A horizontal straight wire of length L extending from east to west is falling with speed v at right angles to the horizontal component of Earth’s magnetic field B. 

(i) Write the expression for the instantaneous value of the e.m.f. induced in the wire. 

(ii) What is the direction of the e.m.f.?

(iii) Which end of the wire is at the higher potential?

In what respect is a toroid different from a solenoid? 

 Draw and compare the pattern of the magnetic field lines in the two cases ?

How is the magnetic field inside a given solenoid made strong?