Define electric potential .

Electric potential at a point is the work done per unit charge in taking a small positive test charge from infinity to that point.

What are the units of electric potential ?

Electric potential is measured in J C -1 or V (volts).

Is electric potential a scalar or vector quantity, and what does its sign indicate?

Electric potential is a scalar quantity, but it carries a positive or negative sign that indicates the sign of the charge producing it.

Electric potential has a value of .......... at infinity.

Electric potential has a value of zero at infinity.

How does the electric potential around an isolated positive charge change as a positive test charge moves closer to it?

The potential increases (becomes more positive) as the test charge moves closer.

True or False? Like gravitational potential, electric potential is always negative.

False. Electric potential takes the sign of the charge producing it — it is positive around a positive charge and negative around a negative charge, unlike gravitational potential, which is always negative.

Define potential gradient .

The potential gradient of an electric field is the rate of change of electric potential with respect to displacement in the direction of the field.

As distance r increases, electric field strength E against r follows a .......... relation.

As distance r increases, electric field strength E against r follows a 1/r 2 relation.

True or False? For a point charge, the V - r graph is steeper than the corresponding E - r graph.

False. The V - r graph is shallower than the corresponding E - r graph, which is the steeper of the two.

How do the key features of a potential-distance ( V - r ) graph differ between a positive and a negative point charge?

For a positive charge: all values of V are positive, following a 1/ r relation For a negative charge: all values of V are negative, following a -1/ r relation

Under what conditions is work done when a charge moves in an electric field?

Work is done when a positive charge moves against the electric field lines, or when a negative charge moves with the electric field lines.

What does the gradient of a graph of electric potential energy E p against distance r represent?

The gradient of an E p - r graph at any point is equal to the electric force F at that point.

True or False? For two like point charges, electric potential energy increases as their separation increases.

False. For two like charges, electric potential energy decreases with separation. It is for two opposite charges that electric potential energy increases with separation.

Define equipotential surfaces .

Equipotential surfaces (or lines in 2D) join together points that have the same electric potential. They are always perpendicular to the electric field lines and are represented by dotted lines.

Describe the shape of the equipotential lines around an isolated point charge.

Concentric circles around the charge, which become progressively further apart with distance.

In a uniform field, such as between two parallel plates, the equipotential lines are horizontal, parallel and .......... .

In a uniform field, such as between two parallel plates, the equipotential lines are horizontal, parallel and equally spaced .

How can the equipotential surface between two like charges be distinguished from that between two opposite charges?

Between two like charges: a region of empty space where the resultant field is zero Between two opposite charges: a central line at a potential of 0 V , where the opposing potentials cancel

A LevelPhysicsAQAFlashcardsFields & Their ConsequencesElectric Potential

Electric Potential (AQA A Level Physics): Flashcards

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Define electric potential.

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Define electric potential.
Electric potential at a point is the work done per unit charge in taking a small positive test charge from infinity to that point.
What are the units of electric potential?
Electric potential is measured in J C^-1 or V (volts).
Is electric potential a scalar or vector quantity, and what does its sign indicate?
Electric potential is a scalar quantity, but it carries a positive or negative sign that indicates the sign of the charge producing it.
Electric potential has a value of .......... at infinity.
Electric potential has a value of zero at infinity.
How does the electric potential around an isolated positive charge change as a positive test charge moves closer to it?
The potential increases (becomes more positive) as the test charge moves closer.
True or False?
Like gravitational potential, electric potential is always negative.
False.
Electric potential takes the sign of the charge producing it — it is positive around a positive charge and negative around a negative charge, unlike gravitational potential, which is always negative.
State the equation for the electric potential V due to a point charge, and define each symbol.
$V = \frac{Q}{4 π ϵ_{0} r}$
- V = electric potential (V)
- Q = magnitude of the charge producing the potential (C)
- r = distance from the centre of the point charge (m)
- ε₀ = permittivity of free space (F m^-1)
How is the total electric potential at a point due to multiple point charges found?
The potentials due to each charge are added together, since electric potential is a scalar quantity, e.g. $V = \frac{Q_{1}}{4 π ϵ_{0} r_{1}} + \frac{Q_{2}}{4 π ϵ_{0} r_{2}}$
Define potential gradient.
The potential gradient of an electric field is the rate of change of electric potential with respect to displacement in the direction of the field.
What does the gradient of a potential-distance (V-r) graph represent, and what equation links electric field strength E to the potential gradient?
The gradient of a V-r graph is equal to the electric field strength E at that point:
$E = - \frac{Δ V}{Δ r}$
The negative sign shows that E opposes the direction of increasing potential.
What does the area under a field strength-distance (E-r) graph represent, and what equation is this graph a representation of?
The area under an E-r graph between two points is equal to the potential difference ΔV between those points. The graph represents:
$E = \frac{Q}{4 π ϵ_{0} r^{2}}$
As distance r increases, electric field strength E against r follows a .......... relation.
As distance r increases, electric field strength E against r follows a 1/r² relation.
True or False?
For a point charge, the V-r graph is steeper than the corresponding E-r graph.
False.
The V-r graph is shallower than the corresponding E-r graph, which is the steeper of the two.
How do the key features of a potential-distance (V-r) graph differ between a positive and a negative point charge?
- For a positive charge: all values of V are positive, following a 1/r relation
- For a negative charge: all values of V are negative, following a -1/r relation
State the equation for the work done ΔW in moving a charge q through a potential difference ΔV.
$Δ W = q Δ V$
State the equation for the electric potential energy E_p of two point charges, and what is true of E_p and V at infinity?
$E_{p} = \frac{Q_{1} Q_{2}}{4 π ϵ_{0} r}$
At infinity, V = 0, so E_p = 0 as well.
Under what conditions is work done when a charge moves in an electric field?
Work is done when a positive charge moves against the electric field lines, or when a negative charge moves with the electric field lines.
What does the gradient of a graph of electric potential energy E_p against distance r represent?
The gradient of an E_p-r graph at any point is equal to the electric force F at that point.
True or False?
For two like point charges, electric potential energy increases as their separation increases.
False.
For two like charges, electric potential energy decreases with separation. It is for two opposite charges that electric potential energy increases with separation.
Define equipotential surfaces.
Equipotential surfaces (or lines in 2D) join together points that have the same electric potential. They are always perpendicular to the electric field lines and are represented by dotted lines.
Describe the shape of the equipotential lines around an isolated point charge.
Concentric circles around the charge, which become progressively further apart with distance.
In a uniform field, such as between two parallel plates, the equipotential lines are horizontal, parallel and ...........
In a uniform field, such as between two parallel plates, the equipotential lines are horizontal, parallel and equally spaced.
How can the equipotential surface between two like charges be distinguished from that between two opposite charges?
- Between two like charges: a region of empty space where the resultant field is zero
- Between two opposite charges: a central line at a potential of 0 V, where the opposing potentials cancel

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