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

Which of the following figures represent the electric field lines due to a single negative charge?

1 volt is equivalent to ______.

The work done in bringing a unit positive charge from infinite distance to a point at distance x from a positive charge Q is W. Then the potential at that point is ______.

Consider a uniform electric field in the z-direction. The potential is a constant ______.

The resistivity of alloy manganin is ______.

A short bar magnet has a magnetic moment of 0. 65 J T^-1, then the magnitude and direction of the magnetic field produced by the magnet at a distance 8 cm from the centre of magnet on the axis is ______.

A solenoid is connected to a battery so that a steady current flows through it. If an iron core is inserted into the solenoid, the current will ______.

If number of turns in primary and secondary coils is increased to two times each, the mutual inductance ______.

We use alloys for making standard resistors because they have ____________.

Two coils are placed close to each other. The mutual inductance of the pair of coils depends upon the ______.

• Assertion (A): An electron has a high potential energy when it is at a location associated with a more negative value of potential, and a low potential energy when at a location associated with a more positive potential.
• Reason (R): Electrons move from a region of higher potential to region of lower potential.

Select the most appropriate answer from the options given below:

"If the slits in Young's double slit experiment are identical, then intensity at any point on the screen may vary between zero and four times to the intensity due to single slit".

Justify the above statement through a relevant mathematical expression.

Draw the intensity distribution as function of phase angle when diffraction of light takes place through coherently illuminated single slit.

In figure, two positive charges q₂ and q₃ fixed along the y axis, exert a net electric force in the + x direction on a charge q1 fixed along the x-axis. If a positive charge Q is added at (x, 0), the force on q₁

(a)

(b)

Figure shows the electric field lines around three point charges A, B and C.

1. Which charges are positive?
2. Which charge has the largest magnitude? Why?
3. In which region or regions of the picture could the electric field be zero? Justify your answer.

(i) near A, (ii) near B, (iii) near C, (iv) nowhere.

In the circuit shown in figure initially, key K₁ is closed and key K₂ is open. Then K₁ is opened and K₂ is closed (order is important). [Take Q₁′ and Q₂′ as charges on C₁ and C₂ and V₁ and V₂ as voltage respectively.]

Then

1. charge on C₁ gets redistributed such that V₁ = V₂
2. charge on C₁ gets redistributed such that Q₁′ = Q₂′
3. charge on C₁ gets redistributed such that C₁V1 + C₂V₂ = C₁E
4. charge on C1 gets redistributed such that Q₁′ + Q₂′ = Q

Calculate potential energy of a point charge – q placed along the axis due to a charge +Q uniformly distributed along a ring of radius R. Sketch P.E. as a function of axial distance z from the centre of the ring. Looking at graph, can you see what would happen if – q is displaced slightly from the centre of the ring (along the axis)?

1. In a quark model of elementary particles, a neutron is made of one up quarks [charge (2/3) e] and two down quarks [charges –(1/3) e]. Assume that they have a triangle configuration with side length of the order of 10^–15 m. Calculate electrostatic potential energy of neutron and compare it with its mass 939 MeV.
2. Repeat above exercise for a proton which is made of two up and one down quark.

Consider a circular current-carrying loop of radius R in the x-y plane with centre at origin. Consider the line intergral

`ℑ(L ) = |int_(-L)^L B.dl|` taken along z-axis.

1. Show that ℑ(L) monotonically increases with L.
2. Use an appropriate Amperian loop to show that ℑ(∞) = µ₀I, where I is the current in the wire.
3. Verify directly the above result.
4. Suppose we replace the circular coil by a square coil of sides R carrying the same current I. What can you say about ℑ(L) and ℑ(∞)?