Physics 22.3 Electric Potential

Question 1

Define electric potential

Answer 1

The electric potential (V) at any point in an electric field is the work done per unit charge on a positive test charge when it is moved from infinity to that position.

Question 2

What are the “important notes” about electric potential?

Answer 2

• The electrical potential at infinity is zero
• Electrical potential is measured in joules per coulomb [J C^-1] or more commonly volts [V]
• Electrical potential is a scalar quantity

Question 3

What is the equation for electric potential?

Answer 3

V=Ep/Q

• V is the electric potential at the position in volts [V]
• Q is the charge of the positive test charge in coulombs [C]
• Ep is the electric potential energy of the charge in joules [J]

Question 4

Define electric potential difference

Answer 4

An electric potential difference (ΔV) is the energy needed to move a unit charge between two points.

Question 6

What is the equation for electric potential difference?

Answer 6

ΔW=QΔV

Question 7

What is the electric potential for a point charge equation?

Answer 7

V=(Q/(4πε0r))

• V is the absolute electric potential in volts [V]
• Q is the charge creating the electric field in coulombs [C]
• r is the distance from the charge in metres [m]
• ε0 is the permittivity of free space in [F m^-1]

Question 9

What are equipotential surfaces?

Answer 9

Equipotential surfaces are locations within a field that have the same electric potential, and as a result no work is done in moving a charge on an equipotential surface.

Question 10

What are the “important notes” for equipotential surfaces?

Answer 10

• Equipotential surfaces are perpendicular to field lines
• Any electrical conductor is an equipotential surface

Question 11

What is a potential gradient?

Answer 11

At any point on an electric field, the potential gradient is the change of potential per unit change of distance in a given direction

Question 12

What is the relation between electric field strength and potential gradient?

Answer 12

The electric field strength is equal to the negative of the potential gradient

Question 13

What is the equation for the relation between electric field strength and potential gradient?

Answer 13

E=-(ΔV/Δx)

• Δv is thee change of potential between two points in volts [V]
• Δx is the distance between the two points in metres [m]
• E is the electric field strength in volts per metre [V m^-1]

Question 14

What is the gradient of a V-r graph?

Electric fields topic

Answer 14

Since E=(Δv/Δx), the electric field strengh can be found from the gradient of a V-r graph.

Question 15

How can ΔV be determined from an E-r graph?

Answer 15

Δv can be determined graphically by finding the area underneath an E-r graph