
Define electrostatic potential and its unit. Obtain expression for electrostatic potential at a point P in the field due to a point charge.
Answer
484.5k+ views
Hint: To answer this question, we have to use the concept of the potential energy for a system of two charges. One of the two charges should be taken as unit positive charge.
Formula Used:
, where is the electrostatic force between the two charges and separated by a distance .
Complete step by step answer:
The electrostatic potential at a point in an electric field is defined as the work done to bring a unit positive charge from infinity to that point without acceleration. For determining the unit of the electrostatic potential, we focus on its definition. It is the work done per unit charge. We know that the SI unit of work is Joule, and that of the charge is Coulomb. So, the unit of electrostatic potential becomes Joule per Coulomb, or .
Let a point charge be fixed at a point A. We consider the electrostatic potential at the point B, at a distance from the point A, as shown below.
Now, as per the definition of the electrostatic potential, we need to bring a unit positive test charge from infinity to the point B without acceleration. The work done in this process will be equal to the electrostatic potential at point B. There are two forces are acting on :
- Electrostatic force due to the point charge
- Force applied externally
Since the test charge should not have acceleration, the net force acting on it must be equal to zero. So
(i)
For the test charge at a distance of from the point A, the electrostatic force on is given by the Coulomb’s law as
From (i)
(ii)
Now, work done in displacing the test charge by
Since the force is parallel to the displacement , so .
From (ii)
As the test charge is brought from infinity to point A, varies from to . Integrating between these limits, we get
Taking the constant outside the integral
Substituting the limits, we get
As the test charge is a unit positive charge, so .
Formula Used:
Complete step by step answer:
The electrostatic potential at a point in an electric field is defined as the work done to bring a unit positive charge from infinity to that point without acceleration. For determining the unit of the electrostatic potential, we focus on its definition. It is the work done per unit charge. We know that the SI unit of work is Joule, and that of the charge is Coulomb. So, the unit of electrostatic potential becomes Joule per Coulomb, or
Let a point charge
Now, as per the definition of the electrostatic potential, we need to bring a unit positive test charge
- Electrostatic force due to the point charge
- Force applied externally
Since the test charge should not have acceleration, the net force acting on it must be equal to zero. So
For the test charge
From (i)
Now, work done in displacing the test charge by
Since the force
From (ii)
As the test charge is brought from infinity to point A,
Taking the constant outside the integral
Substituting the limits, we get
As the test charge
Therefore,
By definition, this is the potential at the point A. Hence the potential due to a point charge at a distance is given by
.
Note: While deriving the expression for the electrostatic potential, do not consider the electrostatic force due to the point charge in the calculation of the work done. The force which is considered is the force applied by an external agent, which is equal and opposite to the electrostatic force.
By definition, this is the potential at the point A. Hence the potential due to a point charge
Note: While deriving the expression for the electrostatic potential, do not consider the electrostatic force due to the point charge in the calculation of the work done. The force which is considered is the force applied by an external agent, which is equal and opposite to the electrostatic force.
Recently Updated Pages
Master Class 12 Economics: Engaging Questions & Answers for Success

Master Class 12 Maths: Engaging Questions & Answers for Success

Master Class 12 Biology: Engaging Questions & Answers for Success

Master Class 12 Physics: Engaging Questions & Answers for Success

Master Class 12 Business Studies: Engaging Questions & Answers for Success

Master Class 12 English: Engaging Questions & Answers for Success

Trending doubts
Which one of the following is a true fish A Jellyfish class 12 biology CBSE

a Tabulate the differences in the characteristics of class 12 chemistry CBSE

Why is the cell called the structural and functional class 12 biology CBSE

Which are the Top 10 Largest Countries of the World?

Differentiate between homogeneous and heterogeneous class 12 chemistry CBSE

Write the difference between solid liquid and gas class 12 chemistry CBSE
