Electric Field | Electric Field Intensity

Electric Field-

 

Electric Field is defined as-

 

The space around an electric charge in which its effect can be experienced is called as its electric field.

OR

It is the space around an electric charge in which any other charge experiences the coulomb force.

 

  • The charge which produces the electric field is called as a source charge.
  • The charge which tests the effect of source charge is called as a test charge.

 

Types of Electric Field-

 

There are following 4 types of electric field-

 

 

  1. Uniform Electric Field
  2. Non-Uniform Electric Field
  3. Variable Electric Field
  4. Constant Electric Field

 

1. Uniform Electric Field-

 

It is an electric field at every point of which a unit positive charge experiences the same electric force.

OR

It is an electric field at every point of which the intensity of electric field remains constant in magnitude and direction.

 

 

In uniform electric field, the electric lines of force are parallel and equidistant.

 

2. Non-Uniform Electric Field-

 

It is an electric field at different points of which a unit positive charge experiences the different electric force.

OR

It is an electric field at different points of which the intensity of electric field is different in magnitude and direction.

 

 

In non-uniform electric field,  the electric lines of force are non-parallel and non-equidistant.

 

3. Variable Electric Field-

 

The electric field which changes with respect to time is called as variable electric field.

E = f(t)

 

4. Constant Electric Field-

 

The electric field which does not depend upon time is called as constant or non-variable electric field.

E ≠ f(t)

 

Electric Field Intensity-

 

Electric Field Intensity is defined as-

 

Electric field intensity at any point is the strength of electric field at that point.

OR

Electric field intensity at any point is the force experienced by a unit positive charge placed at that point.

 

If \overrightarrow{F} is the force acting on a small test charge q0 at any point in the electric field, then electric field intensity \overrightarrow{E} at that point is given by-

 

 

It is important to note that-

  • The test charge q0 may have its own electric field.
  • This may modify the electric field of the source charge.
  • So to minimize this effect, we write \overrightarrow{E} as-

 

 

From the above relation,

Force experienced by any point charge q0 in the electric field of intensity \overrightarrow{E} may be calculated as-

\overrightarrow{F} = q0 . \overrightarrow{E}

 

We know F = ma.

So, acceleration of electric charge q0 having mass m in electric field \overrightarrow{E} may be given as-

 

 

Electric Field Intensity Due To Point Charge-

 

Consider-

  • A point charge Q is placed at any point O.
  • Electric field intensity due to charge Q has to be calculated at any point P.
  • The distance between point O and point P is r units.

 

To calculate the electric field intensity at point P, we place a point charge q0 at point P.

 

 

According to Coulomb’s law,

Force \overrightarrow{F} at point P is given by-

 

 

Also, we know \overrightarrow{E} = \overrightarrow{F} / q0

So,

 

 

This formula gives the electric field intensity due to a point charge Q at distance ‘r’ units from it.

 

This formula shows-

  • Electric field intensity due to any point charge is inversely proportional to the square of the distance from it.
  • As the distance from charge increases, its electric field intensity decreases.
  • Electric field intensity becomes zero at infinity.

 

 

Electric Field Intensity Due To System Of Point Charges-

 

According to principle of superposition of electric charges,

Electric field intensity at a point due to a system of charges is the vector sum of the field intensities due to individual point charges.

 

Hence, the electric field intensity at any point P due to the system of N charges is-

\overrightarrow{E} = \overrightarrow{{E}_1} + \overrightarrow{{E}_2} + \overrightarrow{{E}_3} + ……. + \overrightarrow{E{_N}}

 

Important Points-

 

Point-01:

 

  • Every charge creates an electric field in the space around itself.
  • This electric field extends till infinity.
  • Electric field due to a point charge at its own location is undefined.

 

Point-02:

 

  • Electric field is a vector quantity since it possess both magnitude and direction.
  • The electric field due to a positive point charge is radially outwards away from the charge.
  • The electric field due to a negative point charge is radially inwards towards the charge.

 

Point-03:

 

  • Electric field intensity is a vector quantity since it possess both magnitude and direction.
  • The direction of \overrightarrow{E} is same as that of \overrightarrow{F}.
  • The SI unit of electric field intensity is N/C (Newton per Coulomb).
  • The dimensions of electric field intensity are [MLT-3A-1].

 

Point-04:

 

The value of electric field intensity due to point charge at any point P depends on-

  • Magnitude of the charge
  • Distance of point P from the charge

 

 

It does not depend upon the test charge.

 

Point-05:

 

  • Positive charges like alpha, proton, deutron etc experiences forces in the direction of the electric field.
  • Negative charges like electron experiences force in the direction opposite to the electric field.
  • Neutron experiences no force.

 

Point-06:

 

A point charge q0 is kept in an electric field of strength E and experiences a force F, then-

  • E < F / q0 if field is diverging
  • E = F / q0 if field is uniform
  • E > F / q0 if field is converging

 

To gain better understanding about Electric Field & Electric Field Intensity,

Watch this Video Lecture

 

Next Article- Problems On Electric Field

 

Get more notes and other study material of Class 11 Physics.

Get more notes and other study material of Class 12 Physics.

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Electric Field | Electric Field Intensity
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Electric Field | Electric Field Intensity
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Electric Field is the space around an electric charge in which its effect can be experienced. Electric field intensity at any point is the strength of electric field at that point. Electric Field Intensity Due to Point Charge.
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