## Electric Charges And Fields

- Get to know usually which areas are frequently asked in the CBSE exam
1

## Quantum nature of charge

The smallest charge that can exist is the charge of an electron. Therefore electric charge always exist as an integral multiple of electronic charge (). This is also known as the quantum nature of the charge.

where n = 0, 1, 2, 3 ...................
Find the charge in coulomb on of .
On removing electrons from a metal sheet,then the charge on metal sheet is
A
B
C
D
2

## Electric field due to a charged semicircle

Where
Find force on semicircular ring due to point charge .
3

## Electric field lines

An electric field line is, in general, a curve drawn in such a way that the tangent to it at each point is in the direction of the net field at that point. An arrow on the curve is obviously necessary to specify the direction of electric field from the two possible directions indicated by a tangent to the curve. A field line is a space curve, i.e., a curve in three dimensions.
Why do the electric field lines never cross each other?
4

## Electric field due to a dipole

where is the  angle between the distance vector and dipole.
If be the electric field intensity due to a short dipole at a point on the axis and be that on the right bisector at the same distance from the dipole, then
A
B
C
D
Electric charges and are placed at the corners of an equilateral triangle ABC of side . The magnitude of electric dipole moment of the system is
A
B
C
D
5

## Electric flux through a closed surface in uniform electric field

According to Gauss's Law, flux through a closed surface is given by:

Since electric field is uniform, it is created by a source very far from the closed surface. Or there is no charge enclosed within the closed surface. Hence, net flux through it is zero.
Note:
This argument does not hold true for an open surface as an open surface can be arbitrarily extended to  a closed surface enclosing a non-zero charge in which case the electric flux through the surface may become non-zero.
Which of the following statements are correct?
A
Electric field calculated by Gauss law is the field due to only those charges which are enclosed inside the Gaussian surface
B
Gauss law is applicable only when there is a symmetrical distribution of charge
C
Electric flux through a closed surface will depends only on charges enclosed within that surface only
D
None of these
6

## Electric field due to a conducting cylinder

For

For
A sphere of radius has a volume density of charge . Find the electric field intensity at the surface of the sphere.
A
B
C
D
7

## Electric field due to a uniformly charged thin spherical shell

Figure shows a charged spherical shell of total charge q and radius R and two
concentric spherical Gaussian surfaces, S1 and S2.  as we applied Gauss law to surface S2,for which ,we would find that

Applying Gauss law to surface S1, for which r
where r is the distance from the centre to outside of the shell.
A small conducting sphere carrying charge is surrounded by a spherical uncharged conducting shell. A small charge is placed between the sphere and the shell, then the net charge on the
inner surface of the shell is :
A
B
C
D
none of the above