Define electric potential .

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

Is electric potential a scalar or a vector quantity?

Scalar — it has no direction.

Even though electric potential is a scalar quantity, it can still take a positive or negative sign. What does this sign indicate?

Whether positive work is done moving a test charge from infinity to that point (around a positive charge) or negative work is done (around a negative charge) — not a direction.

Electric potential is positive around an isolated positive charge and .......... around an isolated negative charge.

Electric potential is positive around an isolated positive charge and negative around an isolated negative charge.

True or False? As a positive test charge moves closer to a negative charge, its electric potential increases.

False. As a positive test charge moves closer to a negative charge, its electric potential decreases .

How is the total electric potential at a point due to multiple point charges found?

By adding the potentials due to each individual charge — since potential is a scalar , the total is the simple sum (taking sign into account).

As the distance r from a positive point charge decreases, what happens to the potential V , and why?

V increases — more work must be done on a positive test charge to overcome the repulsive force as it gets closer.

As the distance r from a negative point charge decreases, what happens to the potential V , and why?

V decreases (becomes more negative) — less work is needed on a positive test charge since the attractive force helps it move closer.

Electric potential varies with distance according to 1/ r , whereas electric field strength varies according to .......... .

Electric potential varies with distance according to 1/ r , whereas electric field strength varies according to 1/r 2 .

True or False? The point-charge equation for electric potential cannot be applied to a charged conducting sphere.

False. The equation still applies — the charge on the sphere is treated as if it were concentrated at a point at its centre.

Define the capacitance of a charged sphere.

The charge per unit potential at the surface of the sphere.

In C = Q / V for an isolated sphere, what does the charge Q actually represent?

The charge stored on the surface of the spherical conductor — not the charge of a capacitor pair.

The charge on the surface of a spherical conductor can be treated as a point charge located at its .......... .

The charge on the surface of a spherical conductor can be treated as a point charge located at its centre .

True or False? The capacitance of an isolated sphere increases as its radius increases.

True. Since C = 4π ε 0 R , capacitance is directly proportional to radius R .

If the distance r between two point charges increases by a factor of two, the force F decreases by a factor of .......... .

If the distance r between two point charges increases by a factor of two, the force F decreases by a factor of four .

Name two methods used to estimate the area under a force-distance graph.

Counting squares (if plotted on squared paper), or splitting the area into trapeziums and summing them.

True or False? On a force-distance graph for a point charge, some values of F are negative.

False. All values of F on this graph are positive .

How does the shape of the F - r graph differ from the V - r graph for the same point charge?

The F - r graph starts steeper and declines more rapidly , since force follows an inverse square law (1/ r 2 ) while potential follows a simple inverse law (1/ r ).

What quantity is equal to the change in electric potential energy of a moving charge?

The work done in moving it, Δ W = q Δ V .

When the electric potential V = .......... , the electric potential energy is also zero.

When the electric potential V = zero , the electric potential energy is also zero.

Under what condition is positive work done on a positive charge moving through an electric field?

When it moves against the electric field lines.

Under what condition is positive work done on a negative charge moving through an electric field?

When it moves with the electric field lines.

True or False? In Δ W = q Δ V , Q represents the charge producing the potential.

False. q is the charge being moved ; Q is the (different) charge producing the potential.

A LevelPhysicsOCRFlashcards6. Particles & Medical PhysicsElectric Potential & Energy

Electric Potential & Energy (OCR A Level Physics): Flashcards

Exam code: H556

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FrontElectric Potential
Define electric potential.

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Cards in this collection (31)

Define electric potential.
Electric potential at a point is the work done per unit positive charge in bringing a point test charge from infinity to that point.
Is electric potential a scalar or a vector quantity?
Scalar — it has no direction.
Even though electric potential is a scalar quantity, it can still take a positive or negative sign. What does this sign indicate?
Whether positive work is done moving a test charge from infinity to that point (around a positive charge) or negative work is done (around a negative charge) — not a direction.
What is the electric potential at infinity?
Zero.
Electric potential is positive around an isolated positive charge and .......... around an isolated negative charge.
Electric potential is positive around an isolated positive charge and negative around an isolated negative charge.
True or False?
As a positive test charge moves closer to a negative charge, its electric potential increases.
False.
As a positive test charge moves closer to a negative charge, its electric potential decreases.
How is the total electric potential at a point due to multiple point charges found?
By adding the potentials due to each individual charge — since potential is a scalar, the total is the simple sum (taking sign into account).
State the equation for the electric potential V at a distance r from a point charge Q.
$V = \frac{Q}{4 π ϵ_{0} r}$
As the distance r from a positive point charge decreases, what happens to the potential V, and why?
V increases — more work must be done on a positive test charge to overcome the repulsive force as it gets closer.
As the distance r from a negative point charge decreases, what happens to the potential V, and why?
V decreases (becomes more negative) — less work is needed on a positive test charge since the attractive force helps it move closer.
Electric potential varies with distance according to 1/r, whereas electric field strength varies according to ...........
Electric potential varies with distance according to 1/r, whereas electric field strength varies according to 1/r².
True or False?
The point-charge equation for electric potential cannot be applied to a charged conducting sphere.
False.
The equation still applies — the charge on the sphere is treated as if it were concentrated at a point at its centre.
A Van de Graaff dome (radius 15 cm) is charged to a potential of 240 kV. What is the potential at a distance of 30 cm from the dome's surface (i.e. r = 45 cm from the centre)?
Using Q = 4.0 × 10^-6 C found from the dome's own potential, $V = \frac{Q}{4 π ϵ_{0} r}$ at r = 45 × 10^-2 m gives V ≈ 80 kV.
Define the capacitance of a charged sphere.
The charge per unit potential at the surface of the sphere.
State the equation for the capacitance C of an isolated sphere of radius R.
$C = 4 π ϵ_{0} R$
In C = Q/V for an isolated sphere, what does the charge Q actually represent?
The charge stored on the surface of the spherical conductor — not the charge of a capacitor pair.
The charge on the surface of a spherical conductor can be treated as a point charge located at its ...........
The charge on the surface of a spherical conductor can be treated as a point charge located at its centre.
True or False?
The capacitance of an isolated sphere increases as its radius increases.
True.
Since C = 4πε₀R, capacitance is directly proportional to radius R.
Write the general equation relating capacitance, charge and potential difference.
$C = \frac{Q}{V}$
What does the area under a force-distance (F-r) graph for a point charge represent?
The work done, ΔW.
How does the force F between two point charges vary with their separation r?
F follows an inverse square law: $F = \frac{Q q}{4 π ϵ_{0} r^{2}}$
If the distance r between two point charges increases by a factor of two, the force F decreases by a factor of ...........
If the distance r between two point charges increases by a factor of two, the force F decreases by a factor of four.
Name two methods used to estimate the area under a force-distance graph.
Counting squares (if plotted on squared paper), or splitting the area into trapeziums and summing them.
True or False?
On a force-distance graph for a point charge, some values of F are negative.
False.
All values of F on this graph are positive.
How does the shape of the F-r graph differ from the V-r graph for the same point charge?
The F-r graph starts steeper and declines more rapidly, since force follows an inverse square law (1/r²) while potential follows a simple inverse law (1/r).
State the equation for the work done ΔW when a charge q moves through a potential difference ΔV.
$Δ W = q Δ V$
What quantity is equal to the change in electric potential energy of a moving charge?
The work done in moving it, ΔW = qΔV.
When the electric potential V = .........., the electric potential energy is also zero.
When the electric potential V = zero, the electric potential energy is also zero.
Under what condition is positive work done on a positive charge moving through an electric field?
When it moves against the electric field lines.
Under what condition is positive work done on a negative charge moving through an electric field?
When it moves with the electric field lines.
True or False?
In ΔW = qΔV, Q represents the charge producing the potential.
False.
q is the charge being moved; Q is the (different) charge producing the potential.

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