ELECTROSTATIC POTENTIAL AND CAPACITANCE
Electrostatic Potential Energy (U)(PYQ 2020,2018,2014,2010)
Electrostatic potential energy of a body at a point in an electric field can be defined as the work done by external force
in moving a charge (slowly, without acceleration) from infinity to the given point, against the field. SI Unit is Joule.
Derivation (PYQ 2020)
Consider a source charge Q at origin and another charge q at infinity. An external force Fext acts on q such that it is equal
in magnitude but opposite in direction the Coulomb force between Q and q. So the work done by Fext on q on ing it by a
distance dx is-
Note: 1) We cannot calculate absolute potential energy of a body; we can only calculate the difference in potential
energy of the body between two points.
2) Electrostatic force is a conservative force so work done and hence potential energy difference only depends on the
initial and final positions of the object
ELECTROSTATIC POTENTIAL (V) (PYQ 2018, 2016, 2012, 2011)
Electrostatic potential at a point in an electric field is defined as the work done by external force to bring a unit positive
charge (slowly, without acceleration) from infinity to the given point.(SI Unit- joule/coulomb or Volt)
By definition,
,Note: We cannot calculate absolute potential at a point; we can only calculate the potential difference between two
points.
*To derive expression for potential, just substitute Q2 for 1 in the derivation for U.
Ques: Draw a graph showing variation of potential (V) and distance (r) (PYQ 2012)
Ans:
Similar PYQs
POTENTIAL DUE TO AN ELECTRIC DIPOLE (PYQ 2019)
Consider a dipole of dipole moment p and length 2a. Let us calculate the potential at a point O at a distance r from the
center of the dipole.
, Important PYQs
Ques: Derive an expression for the electrostatic potential at any point along the axial line of a dipole (PYQ 2019)
POTENTIAL DUE TO A SYSTEM OF CHARGES
Total potential at a point due to a system of charges
is equal to the algebraic sum of potentials due to all
the individual charges at that point.
Note: In the previous chapter we saw that electric field inside a charged hollow sphere is 0. So potential inside the shell
is constant and is equal to its value at the surface as no work is done on moving a charge inside the shell.
Important PYQs
Ques: The potential at the surface of a spherical hollow metal shell with radius 6cm is 12V. What will be the potential at
its center? (PYQ 2011)
Ans: Since the electric field inside a shell is 0, no work is done to move a charge inside the shell therefore potential at
the center will be the same as the potential at its surface i.e. 12V
EQUIPOTENTIAL SURFACES (PYQ 2020, 2019, 2014, 2013, 2010)
Equipotential surfaces are surfaces which have a
Constant value of potential at all points.
Electrostatic Potential Energy (U)(PYQ 2020,2018,2014,2010)
Electrostatic potential energy of a body at a point in an electric field can be defined as the work done by external force
in moving a charge (slowly, without acceleration) from infinity to the given point, against the field. SI Unit is Joule.
Derivation (PYQ 2020)
Consider a source charge Q at origin and another charge q at infinity. An external force Fext acts on q such that it is equal
in magnitude but opposite in direction the Coulomb force between Q and q. So the work done by Fext on q on ing it by a
distance dx is-
Note: 1) We cannot calculate absolute potential energy of a body; we can only calculate the difference in potential
energy of the body between two points.
2) Electrostatic force is a conservative force so work done and hence potential energy difference only depends on the
initial and final positions of the object
ELECTROSTATIC POTENTIAL (V) (PYQ 2018, 2016, 2012, 2011)
Electrostatic potential at a point in an electric field is defined as the work done by external force to bring a unit positive
charge (slowly, without acceleration) from infinity to the given point.(SI Unit- joule/coulomb or Volt)
By definition,
,Note: We cannot calculate absolute potential at a point; we can only calculate the potential difference between two
points.
*To derive expression for potential, just substitute Q2 for 1 in the derivation for U.
Ques: Draw a graph showing variation of potential (V) and distance (r) (PYQ 2012)
Ans:
Similar PYQs
POTENTIAL DUE TO AN ELECTRIC DIPOLE (PYQ 2019)
Consider a dipole of dipole moment p and length 2a. Let us calculate the potential at a point O at a distance r from the
center of the dipole.
, Important PYQs
Ques: Derive an expression for the electrostatic potential at any point along the axial line of a dipole (PYQ 2019)
POTENTIAL DUE TO A SYSTEM OF CHARGES
Total potential at a point due to a system of charges
is equal to the algebraic sum of potentials due to all
the individual charges at that point.
Note: In the previous chapter we saw that electric field inside a charged hollow sphere is 0. So potential inside the shell
is constant and is equal to its value at the surface as no work is done on moving a charge inside the shell.
Important PYQs
Ques: The potential at the surface of a spherical hollow metal shell with radius 6cm is 12V. What will be the potential at
its center? (PYQ 2011)
Ans: Since the electric field inside a shell is 0, no work is done to move a charge inside the shell therefore potential at
the center will be the same as the potential at its surface i.e. 12V
EQUIPOTENTIAL SURFACES (PYQ 2020, 2019, 2014, 2013, 2010)
Equipotential surfaces are surfaces which have a
Constant value of potential at all points.
