Science (English Medium) Class 12 - CBSE Important Questions

Explain, giving reasons, the basic difference in converting a galvanometer into (i) a voltmeter and (ii) an ammeter?

Two long straight parallel conductors carrying steady currents I₁ and I₂ are separated by a distance 'd'. Explain briefly, with the help of a suitable diagram, how the magnetic field due to one conductor acts on the other. Hence deduce the expression for the force acting between the two conductors. Mention the nature of this force.

Draw a labelled diagram of a moving coil galvanometer and explain its working. What is the function of radial magnetic field inside the coil?

Define the term ‘current sensitivity’ of a moving coil galvanometer.

Beams of electrons and protons move parallel to each other in the same direction. They ______.

A long straight wire of radius 'a' carries a steady current 'I'. The current is uniformly distributed across its area of cross-section. The ratio of the magnitude of magnetic field `vecB_1` at `a/2` and `vecB_2` at distance 2a is ______.

Two long parallel wires kept 2 m apart carry 3A current each, in the same direction. The force per unit length on one wire due to the other is ______.

Give two points to distinguish between a paramagnetic and a diamagnetic substance ?

State Gauss’s law in electrostatics. A cube which each side ‘a’ is kept is an electric field given by `vecE` = C × l. (as is shown in the figure where C is a positive dimensional constant. Find out

(i) The electric flux through the cube, and

(ii) The net charge inside the cube.

Answer the following question.
Write three points of differences between para-, dia- and ferromagnetic materials, giving one example for each. 

• Assertion (A): Diamagnetic substances exhibit magnetism.
• Reason (R): Diamagnetic materials do not have a permanent magnetic dipole moment.

Which of the following has a permeability less than that of free space?

A horizontal straight wire 10 m long extending from east to west is falling with a speed of 5.0 m s⁻¹, at right angles to the horizontal component of the earth’s magnetic field, 0.30 × 10⁻⁴ Wb m⁻².

1. What is the instantaneous value of the emf induced in the wire?
2. What is the direction of the emf?
3. Which end of the wire is at the higher electrical potential?

A circular coil of cross-sectional area 200 cm² and 20 turns is rotated about the vertical diameter with angular speed of 50 rad s⁻¹ in a uniform magnetic field of magnitude 3.0 × 10⁻²T. Calculate the maximum value of the current in the coil.

When Puja, a student of 10^th class, watched her mother washing clothes in the open, she observed coloured soap bubbles and was curious to know why the soap bubbles appear coloured. In the evening when her father, an engineer by profession, came home, she asked him this question. Her father explained to her the basic phenomenon of physics due to which the soap bubbles appear coloured.
(a) What according to you are the values displayed by Puja and her father?
(b) State the phenomenon of light involved in the formation of coloured soap bubbles.

A bar magnet is moved in the direction indicated by the arrow between two coils PQ and CD. Predict the directions of induced current in each coil.

Answer the following question.
When an inductor is connected to a 200 V dc voltage, a current at 1A flows through it. When the same inductor is connected to a 200 V, 50 Hz ac source, only 0.5 A current flows. Explain, why? Also, calculate the self-inductance of the inductor. 

Define 'quality factor' of resonance in a series LCR circuit. What is its SI unit?

Write the function of a transformer.

A device 'X' is connected to an ac source V = V₀ sin ωt. The variation of voltage, current and power in one cycle is shown in the following graph:

(a) Identify the device 'X'.
(b) Which of the curves A, B and C represent the voltage , current and the power consumed in the circuit? Justify your answer.
(c) How does its impedance vary with frequency of the ac source? Show graphically.
(d) Obtain an expression for the current in the circuit and its phase relation with ac voltage.