Electric Fields

Question 1

What is a force field ?

Answer 1

A field is a region where each point is affected by a non- contact force.

Question 2

What did Richard Feynman describe a field to be ?

Answer 2

Something that has the potential to produce a force.

Question 3

What is an electric field ?

Answer 3

A region where a charge is affected by the electrostatic force

Question 4

What is a difference between the gravitational field and electric field ?

Answer 4

Gravitational fields are always attractive unlike electric fields which are attractive and repulsive depending on the charges in the field

Question 5

What does Coulomb’s law state ?

Answer 5

Any two objects with a charge will experience a force inversely proportional to the square of the distance between them and directly proportional to the product of the two charges

Question 6

Which fields follow the inverse square law ?

Answer 6

Gravitational and electric fields

Question 7

What is the force produced when there are two objects ?

Answer 7

F= k Qq/ r^2

Question 8

What is the constant k in F = k Qq/r^2 ?

Answer 8

1/4 pi epsilon0 = 8.99*10 ^9

Question 9

What is permittivity ?

Answer 9

A measure of how difficult it is to generate an electric field within a material

Question 10

If a material has a higher permittivity would it be harder or easier to generate an electric field?

Answer 10

It would be harder to generate an electric field as they are better insulators

Question 11

What is the permittivity of free space?

Answer 11

The permittivity of the air

Question 12

How can you calculate the electric field strength ?

Answer 12

E= kQ/r^2

Question 13

What is the electric field strength ?

Answer 13

The electric force exerted per unit positive charge at a point within the field

Question 14

What do you get when you substitute E (electric field strength) within columbs law equation ?

Answer 14

F=Eq

Question 15

What do electric field lines show ?

Answer 15

They convey the direction of force experienced by a positive charge placed in the field

Question 16

What will the resultant field be when the electric fields are in the same direction ?

Answer 16

E1 +E2

Question 17

What will the resultant field be if the electric fields are in opposite directions ?

Answer 17

E1-E2

Question 18

What are the factors that impact the direction of the resultant field ?

Answer 18

-the type of charge (like charge .. )
- the magnitude of the charges

Question 19

Where to radial electric fields exist ?

Answer 19

Between point charges and around uniform spheres

Question 20

How can you tell that the fields get weaker as the distance increases from point charges ?

Answer 20

The field lines separation increases (weaker )

Question 21

Where do uniform electric fields typically exist ?

Answer 21

Between charges metal plates and electrodes

Question 22

What are the field lines like in a uniform electric field?

Answer 22

They would be parallel lines that are equally spaced

Question 23

What is the difference in force experienced within a radial and uniform field.

Answer 23

The force experienced in a uniform electric field is constant throughout whereas in a radial field the force decreases as the distance increases

Question 24

How do you dare field lines in an electric field ?

Answer 24

From the positive to negative and perpendicular to the component

Question 25

What is the null point ?

Answer 25

A point within the field where the resultant force and the field strength is 0

Question 26

What happens when a charged particle (an electron) interacts with an uncharged particle?

Answer 26

The electron would repel the negative charges pushing them away and the positive charges closer to the surface

Question 27

How can you calculate the electric field strength for a uniform field ?

Answer 27

E=V/d - Work done by the field from moving the charge from one plate to another (W=Fd ) -electric potential difference ( the work done per unit charge in moving the charge between two points (W/q =V ) (w= qV ) - Fd =qV Sub F = Eq gives us E= v/d

Question 28

What are the two units for the electric field strength ?

Answer 28

Vm^-1 and Nc^-1 (newtons per columb )

Question 29

What happens if a charged particle is placed in an electric field ?

Answer 29

The particle will experience a force that will cause it to accelerate

Question 30

What happens if a positive charge at rest had been placed in a uniform electric field ?

Answer 30

It will move parallel along the field line

Question 31

What happens if a negative particle at rest had been placed in a uniform field ?

Answer 31

It will accelerate in parallel against the field lines

Question 32

What happens if a charged particle in motion is placed within a uniform field ?

Answer 32

It will experience a constant electric force (uniform ) travelling in a parabolic shape (trajectory ) depending on the charge of the particle

Question 33

What are the factors affecting the deflection when a charged particle in motion travels through a uniform electric field ?

Answer 33

- greater mass - smaller deflection -greater the charge - the greater deflection - greater speed - less deflection

Question 34

What is electric potential ?

Answer 34

The work done /potential energy per unit positive charge to move a positive charge from infinity to a point within the field (against the field )

Question 35

What is the electric potential at a distance of infinity?

Answer 35

0

Question 36

How can you work out the electric potential of a point ?

Answer 36

V= W / q = kQ/ r

Question 37

When is the electric potential positive ?

Answer 37

When work is done against the field ( like charges reppel) positive charge

Question 38

When is the electric potential negative ?

Answer 38

When work is done by the field ( opposite charges attracting ) negative charge

Question 39

What is the gradient of a v against r graph ?

Answer 39

The electric field strength

Question 40

For a negative charge as r increases what happens to the potential ?

Answer 40

The potential increases

Question 41

What does the area under an electric field strength against r graph give ?

Answer 41

The electric potential -change in potential from r1 to r2