Electric Charges and Fields 2

Question 1

what are point charges

Answer 1

If the sizes of charged bodies are very small as compared to the
distances between them, we treat them as point charges. All the
charge content of the body is assumed to be concentrated at one point
in space.

Question 2

what are the basic properties of charge

Answer 2

i) Charges are additive in nature. It is a scalar like mass but mass is always +ve while charge canbe -ve/+ve.

ii) Conservation of charges:
Total electric charge of an isolated system, remains constant, regardless of charges within the system itself.

This means that charges cannot be created or destroyed. It can only be transferred from one body to another by certain methods like induction, conduction

Question 3

charges are quantised. justify

Answer 3

Experimentally it is established that all free charges are integral multiples
of a basic unit of charge denoted by e. Thus charge q on a body is always
given by
q = ne

This basic unit of charge is the charge that an electron or proton carries.

Question 4

what is the reason behind quantisationof charged

Answer 4

The reason behind quantisation is that when electrons are transferred from one body to another, only an integral multiple of them will get transferred.

quantisation of charge is possible only at the microscopic level and can be ignored at the macroscopic level because there is a large charge at the level of macroscopic systems due wto which quantised charge is negligible.

Question 5

what are the similarities and differences between mass and charge

Answer 5

similarities
- both are scalar
- both are conserved

differences
- mass can only be +ve while charge can be +ve/-ve/o
- mass varies with velocity while charge is independent of speed.
- charge cannot exist without mass but mass can exist without charge.

Question 6

state coulomb’s law of electrostatic force

Answer 6

The force of attraction or repulsion between 2 stationary charges is directly proportional to the product of the 2 charges and iversely proprtional to the square of the distance between them. The force acts along the line joining their centres.

Question 7

what is electrostatic force constant

Answer 7

F α q1q2
F α ⅟r^2

combining
Fα q1q2/r^2
F= kq1q2/r^2

K is the electrostatic force constant. It depends on the nature of the medium and the system of units.

k=1/4πε₀

Question 8

what is epsilon not?

Answer 8

epsilon not is called the permittivity of free space. Permittivity is the property of charges which determined the electric force of 2 charges situated in a given medium/

Question 9

what is relative permittivity

Answer 9

Relative permittivity is the ratio of the forces between 2 charges in free space to the force between the same in charges in any other medium, placed at the same distance.
F₀/Fm= E/E₀= Er

Question 10

what is principle of super position

Answer 10

force on any
charge due to a number of other charges is the vector
sum of all the forces on that charge due to the other
charges, taken one at a time. The individual forces
are unaffected due to the presence of other charges.
This is termed as the principle of superposition.

Question 11

define electric field

Answer 11

the
electric field due to a charge Q at a point in space may be defined
as the force that a unit positive charge would experience if placed at that point.

Question 12

what is source charge and test charge

Answer 12

The charge Q, which is producing the electric field, is
called a source charge and the charge q, which tests the effect of a
source charge, is called a test charge

Question 13

what are the features of a test charge

Answer 13

The test charge should be too small for not disturbing the source charge and the ratio F/q should be finite.

Question 14

what is the electric field depend upon

Answer 14

Electric field at a point is dependent to the magnitude of the source charge and is independent of the test charge. It is inversely dependent on distance r from the source to charge.

Question 15

what is the direction of electric field

Answer 15

For a positive charge, the electric field will be directed radially
outwards from the charge. On the other hand, if the source charge is
negative, the electric field vector, at each point, points radially inwards.

Question 16

electric field has spherical symmetry

Answer 16

at equal distances from the charge Q, the magnitude
of its electric field E is same. The magnitude of electric field E due to
a point charge is thus same on a sphere with the point charge at its
centre; in other words, it has a spherical symmetry.

Question 17

what is the physical significance of electric field

Answer 17

It characterises the electrical environment of a system of charges. It gives information of the force on a unit +ve charge placed at that point and is idendpendent of the test charge.

The true physical significance of the concept of electric field, however,
emerges only when we go beyond electrostatics and deal with timedependent electromagnetic phenomena.