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

A thin straight infinitely long conducting wire having charge density λ is enclosed by a cylindrical surface of radius r and length l, its axis coinciding with the length of the wire. Find the expression for the electric flux through the surface of the cylinder.

Figure shows three point charges +2q, −q and + 3q. Two charges + 2q and −q are enclosed within a surface ‘S’. What is the electric flux due to this configuration through the surface ‘S’?

In which orientation, a dipole placed in a uniform electric field is in (i) stable, (ii) unstable equilibrium?

A thin conducting spherical shell of radius R has charge Q spread uniformly over its surface. Using Gauss’s law, derive an expression for an electric field at a point outside the shell.

Draw a graph of electric field E(r) with distance r from the centre of the shell for 0 ≤ r ≤ ∞.

Draw the pattern of electric field lines, when a point charge –Q is kept near an uncharged conducting plate.

State Gauss’s law for magnetism. Explain its significance. 

Answer the following question.
Draw the pattern of electric field lines when a point charge +q is kept near an uncharged conducting plate.

Answer the following question.
Derive an expression for the electric field due to a dipole of dipole moment `vec"p"` at a point on its perpendicular bisector.

Answer the following question.
State Gauss's law for magnetism. Explain its significance.

Deduce the expression for the torque `vec"τ"` acting on a planar loop of area `vec"A"` acting on a planar loop of area `vec"B"`. If the loop is free to rotate, what would be its orientation in stable equilibrium?

State Gauss's law in electrostatics. Show, with the help of a suitable example along with the figure, that the outward flux due to a point charge 'q'. in vacuum within a closed surface, is independent of its size or shape and is given by `q/ε_0`

State Gauss’s law on electrostatics and drive expression for the electric field due to a long straight thin uniformly charged wire (linear charge density λ) at a point lying at a distance r from the wire.

An electric dipole is placed at an angle of 30° with an electric field intensity of 2 × 10⁵ N/C. It experiences a torque equal to 4 Nm. The charge on the dipole, if the dipole length is 2 cm, is ______.

According to Coulomb's law, which is the correct relation for the following figure?

Which of the following statements about nuclear forces is not true?

The electric potential V as a function of distance X is shown in the figure.

The graph of the magnitude of electric field intensity E as a function of X is ______.

1. Obtain the expression for the electric field intensity due to a uniformly charged spherical shell of radius R at a point distant r from the centre of the shell outside it.
2. Draw a graph showing the variation of electric field intensity E with r, for r > R and r < R.

Two large, thin metal plates are parallel and close to each other. On their inner faces, the plates have surface charge densities of opposite signs and of magnitude 17.7 × 10^–22 C/m². What is electric field intensity E:

1. in the outer region of the first plate, and
2. between the plates?

An isolated point charge particle produces an electric field `vecE` at a point 3 m away from it. The distance of the point at which the field is `vecE/4` will be ______.