7.3 Electric Fields

Question 1

Coulomb’s Law

Answer 1

states that the magnitude of the force between two point charges is
directly proportional to the product of their charges, and inversely proportional to the
square of the distance between the charges.

Question 2

When is the force attractive?

Answer 2

When both charges are different

Question 3

When is the force repulsive?

Answer 3

When both charges are the same

Question 4

Electric field strength

Answer 4

is the force per unit charge experienced by an object in an electric field.

Question 5

How to find out whether a
particle is charged, and whether its charge is negative or positive ?

Answer 5

• This is done by firing the particle
  at right angles to the field and observing its path
• A charged particle will experience a constant
  electric force either in or opposite to the direction of the field (depending on its charge), this
  causes the particle to accelerate and so it follows a parabolic shape

Question 5

Difference between radial field and uniform field

Answer 5

• A uniform field exerts
  that same electric force everywhere in the field, as shown by the parallel and equally spaced field
  lines
• whereas in a radial field the magnitude of electric force depends on the distance between
  the two charges.

Question 6

How do you know if the particle has a positive charge from a graph?

Answer 6

The parabolic shape must be in the direction of the field.

Question 7

How do you know if the particle has a negative charge from a graph?

Answer 7

The parabolic shape must move opposite to the
direction of the field.

Question 8

How do you know if the charge (Q) is positive from radial field

Answer 8

Electric field lines point away from Q

Question 9

How do you know if the charge (Q) is negative from radial field

Answer 9

Electric field lines point towards Q

Question 10

electric potential (V)

Answer 10

is electric potential energy per unit positive charge

Question 11

At an infinite distance from Q

Answer 11

A charged particle q would have zero potential energy

Question 12

What does the gradient of a tangent give you

Answer 12

gives the electric point at that point

Question 13

What happens to the charge in a repulsive field

Answer 13

The charge q gains potential energy as r decreases

Question 14

What happens to the charge in a attractive field

Answer 14

The charge q gains potential energy as r increases

Question 15

What does the value of potential ( positive or negative) depend on

Answer 15

depends on the sign of the charge (Q),

Question 16

when the charge is positive

Answer 16

potential is positive and the charge is repulsive,

Question 17

when the charge
is negative

Answer 17

potential is negative and the force is attractive

Question 18

What is the gradient of a tangent to a potential (V) against distance (r) graph

Answer 18

gives the value of
electric field strength (E) at that point

Question 19

Electric potential difference

Answer 19

is the energy needed to move a unit charge between two
points.

Question 20

What surfaces to electric fields have

Answer 20

equipotential surfaces

Question 21

what is the potential on an
equipotential surface

Answer 21

the same everywhere, therefore when a charge moves along an
equipotential surface, no work is done.

Question 22

How is a uniform field strength produced

Answer 22

by connecting two parallel plates to the opposite poles of a battery

Question 23

what do you get under the area of a graph of electric field strength (E) against distance (r)

Answer 23

you can find the electric potential difference

Question 24

when is the absolute magnitude of electric potential at its greatest

Answer 24

at the surface of a charge, and as the distance from the charge increases, the potential decreases
so electric potential at infinity is zero.

Question 25

Define electric potential at a point in an electric field

Answer 25

The electric potential at a point in an electric field is the work done per unit charge when a point positive charge is moved from infinity to the point.