6.2 Electric Fields

Question 1

Define Electric Field

Answer 1

A region of space in which charged particles
are subject to an electrostatic force

Question 2

What shape of field do point charges
have?

Answer 2

Radial fields.

Question 3

How can you model uniformly charged
spheres?

Answer 3

As a point charge at the centre of the sphere.

Question 4

What do field lines show?

Answer 4

The path a positive test charge would take
when placed in an Electric Field.

Question 5

What do field lines show?

Answer 5

The path a positive test charge would take
when placed in an Electric Field.

Question 6

Which direction do the field lines point?

Answer 6

Positive to negative – the lines always point
away from a positive charge and towards a
negative charge

Question 7

What effect does distance have on the
strength of the electrostatic force?

Answer 7

The greater the distance, the weaker the
force.

Question 8

How is the strength of an Electric Field
represented in a diagram?

Answer 8

By how close together the field lines are – the
closer the lines, the stronger the field.

Question 9

Define Electric Field Strength

Answer 9

Force per unit charge on a positive test
charge placed in the field

Question 10

What is the formula for Electric Field
Strength?

Answer 10

E = F ÷ Q

Question 11

What is Coulomb’s Law?

Answer 11

The force between any two point charges is
proportional to the product of their charges
and inversely proportional to the square of the
distance between them.

Question 12

What is the formula for the force
between two point charges?
(Coulomb’s Law)

Answer 12

F= (Qq)/4pi(epsilon)r^2

Question 13

Define permittivity

Answer 13

The ability of a material to transmit an Electric
Field (how easily the atoms become
polarised).

Question 14

What is the formula for the Electric Field
Strength of a point charge?

Answer 14

E=Q/(4pi(epsilon)r^2)

Question 15

What is the formula for the Electric Field
Strength of a point charge?

Answer 15

E=Q/(4pi(epsilon)r^2)

Question 16

Name some similarities between
Gravitational and Electric Fields

Answer 16

● Both follow the inverse square law for the force.
● Point masses and point charges both produce a radial field.
● Newton’s law and Coulomb’s law formulae for force are very
similar:
● Field strength is defined by
force per unit charge/mass

Question 17

Name some differences between
Gravitational and Electric Fields

Answer 17

● Gravitational fields are always attractive, Electric Fields
can be attractive or repulsive (depending on the charge).
● The constants of proportionality in Newton’s Law and
Coulomb’s Law are different:

Question 18

Name some differences between
Gravitational and Electric Fields

Answer 18

● Gravitational fields are always attractive, Electric Fields
can be attractive or repulsive (depending on the charge).
● The constants of proportionality in Newton’s Law and
Coulomb’s Law are different:

Question 19

What is the formula for the work done
when moving a charge in an Electric
Field?

Answer 19

Work done = Force x Distance moved

Question 20

Define potential at a point in an Electric
Field

Answer 20

The work done per unit charge in moving a
positive test charge from infinity to that point
in the Electric Field.

Question 21

What is the formula for the potential at a
point in an Electric Field?

Answer 21

V=E/Q

Question 22

What is the formula for the potential
between two parallel plates?

Answer 22

E=V/d

Question 23

What can the motion of charged particles
in an Electric Field be modelled as?

Answer 23

Projectile motion: the two components of
velocity are independent of each other.
Velocity perpendicular to the field is not
affected, velocity parallel to the field is.

Question 24

How do you calculate the parallel
component of velocity for a charged
particle in a uniform Electric Field?

Answer 24

1. First, calculate the time the particle is in the field (using time
   = distance/speed, where distance = length of charged
   plates and speed = velocity perpendicular to the field).
2. Use a = F/m and F=Eq to calculate the acceleration of the
   particle while it is in the field (a = Eq / m).
3. Substitute these values into V = u + at where u is the initial
   parallel velocity and V is the final parallel velocity

Question 25

What is the formula for the potential near
a point charge?

Answer 25

V=Q/(4pi(epsilon)r)

Question 26

What does the force-distance graph for a
point/spherical charge look like?

Answer 26

Force is inversely
proportional to the
square of the
distance.

Question 27

What does the area under a
force-distance graph for a point/spherical
charge represent?

Answer 27

The work done
in moving the
charge.

Question 28

What is the formula for electric potential
energy near a point charge?

Answer 28

E=Vq

Question 29

What is the formula for electric potential
energy near a point charge?

Answer 29

E=Vq

Question 30

What is the formula for the capacitance
of an isolated sphere?

Answer 30

Isolated spheres can store charge, so technically they can
be classed as capacitors.
Using C = Q ÷ V and the
formula for V (in terms of
Coulomb’s law), you can
derive the formula for
capacitance:

Question 31

What is the formula for electric potential
energy near a point charge?
(Coulomb’s Law)

Answer 31

E=(Qq)/(4pi(epsilon)r)