Lesson test: Electric potential

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Electric potential

1.[2p]
Why does a potential exist for the electric force at all?

The force is central and depends only on distance, so the work between two points is independent of the path

Correct

Because charge is quantised

The answer is: The force is central and depends only on distance, so the work between two points is independent of the path

Because the field obeys Gauss's law

The answer is: The force is central and depends only on distance, so the work between two points is independent of the path

Because potential is defined to be zero at infinity

The answer is: The force is central and depends only on distance, so the work between two points is independent of the path

2.[2p]
A charge of $+ 6.0$ nC and a charge of $- 2.0$ nC each sit 5.0 cm from a point P. What is the potential at P, in volts?

CorrectNot quite: 719

3.[1p]
Potentials from several charges add as ordinary numbers, with no components to resolve.

True

Correct

False

The answer is: True

4.[2p]
The field component along a direction equals

minus the rate of change of potential along that direction

Correct

the potential divided by the distance from the charge

The answer is: minus the rate of change of potential along that direction

the rate of change of potential along that direction

The answer is: minus the rate of change of potential along that direction

the potential times the charge

The answer is: minus the rate of change of potential along that direction

5.[3p]
A proton is accelerated from rest through a potential difference of 1.50 kV. What is its final speed, in units of $10^{5}$ metres per second?

CorrectNot quite: 5.36

6.[2p]
Why is a conductor in electrostatic equilibrium an equipotential volume?

The field inside is zero, so no work is done moving a charge anywhere within it

Correct

Because charge sits only on its surface

The answer is: The field inside is zero, so no work is done moving a charge anywhere within it

Because conductors have no resistance

The answer is: The field inside is zero, so no work is done moving a charge anywhere within it

Because the potential at infinity is defined as zero

The answer is: The field inside is zero, so no work is done moving a charge anywhere within it

7.[3p]
Two conducting spheres of radii 10 cm and 5.0 cm are joined by a long wire and given 30 nC in total. How much charge, in nanocoulombs, ends up on the smaller sphere?

CorrectNot quite: 10

8.[2p]
A person charged to 10 kV by walking across a carpet is startled rather than hurt because

the stored energy is tiny, since the total charge involved is tiny

Correct

10 kV is below the threshold at which current can flow through skin

The answer is: the stored energy is tiny, since the total charge involved is tiny

the charge sits on clothing rather than on the body

The answer is: the stored energy is tiny, since the total charge involved is tiny

potential differences are never dangerous, only fields are

The answer is: the stored energy is tiny, since the total charge involved is tiny

9.[3p]
Match each quantity to what it belongs to.

Electric field
Force
Potential
Potential energy

a charge, or a pair of charges
a charge sitting at that point
a point in space, per unit charge
a point in space, energy per unit charge

Show the answer

Electric field: a point in space, per unit charge Force: a charge sitting at that point Potential: a point in space, energy per unit charge Potential energy: a charge, or a pair of charges

1.[2p] Why does a potential exist for the electric force at all?

2.[2p] A charge of +6.0 nC and a charge of −2.0 nC each sit 5.0 cm from a point P. What is the potential at P, in volts?

3.[1p] Potentials from several charges add as ordinary numbers, with no components to resolve.

4.[2p] The field component along a direction equals

5.[3p] A proton is accelerated from rest through a potential difference of 1.50 kV. What is its final speed, in units of 105 metres per second?

6.[2p] Why is a conductor in electrostatic equilibrium an equipotential volume?

7.[3p] Two conducting spheres of radii 10 cm and 5.0 cm are joined by a long wire and given 30 nC in total. How much charge, in nanocoulombs, ends up on the smaller sphere?

8.[2p] A person charged to 10 kV by walking across a carpet is startled rather than hurt because

9.[3p] Match each quantity to what it belongs to.

1.[2p]
Why does a potential exist for the electric force at all?

2.[2p]
A charge of $+ 6.0$ nC and a charge of $- 2.0$ nC each sit 5.0 cm from a point P. What is the potential at P, in volts?

3.[1p]
Potentials from several charges add as ordinary numbers, with no components to resolve.

4.[2p]
The field component along a direction equals

5.[3p]
A proton is accelerated from rest through a potential difference of 1.50 kV. What is its final speed, in units of $10^{5}$ metres per second?

6.[2p]
Why is a conductor in electrostatic equilibrium an equipotential volume?

7.[3p]
Two conducting spheres of radii 10 cm and 5.0 cm are joined by a long wire and given 30 nC in total. How much charge, in nanocoulombs, ends up on the smaller sphere?

8.[2p]
A person charged to 10 kV by walking across a carpet is startled rather than hurt because

9.[3p]
Match each quantity to what it belongs to.