7.4 - Electric Fields

Question 1

What produces an electric field?

Answer 1

All charged particles produce an electric field around them.

Question 2

What is a point charge?

Answer 2

For a point outside a spherical conductor, its charge may be considered to be a point charge at its centre. The electric field lines are radial.

Question 3

What is Coulomb’s law?

Answer 3

The electrostatic force between 2 point charges is proportional to the product of the charges and inversely proportional to the square of their separation.

Question 4

What is the Coulomb equation?

Answer 4

Fₑ = Q1Q2/4πε₀r²
Fₑ = electrostatic force between 2 charges (N)
Q1 and Q2 = 2 point charges (C)
ε₀ = permittivity of free space
r = distance between the centre of the charges (m)

Question 5

what is ε₀?

Answer 5

A constant which represents the capability of an electric field to permeate a vacuum.

Question 6

If there is a positive and negative charge, is the electrostatic force positive or negative and how would this force be interpreted?

Answer 6

Negative, therefore interpreted as an attractive force (since opposite charges attract).

Question 7

If the charges are the same, is the electrostatic force positive or negative and how is this force interpreted?

Answer 7

Positive, interpreted as a repulsive force (as same charges repulse)

Question 8

What is an example of a spherical conductor?

Answer 8

A charged metal sphere.

Question 9

Which direction do the electric field lines of a uniform conductor with a positive charge go?

Answer 9

Outwards

Question 10

Which direction do the electric field lines of a uniform conductor with a negative charge go?

Answer 10

Inwards.

Question 11

What is electric field strength?

Answer 11

The electrostatic force per unit positive charge acting on a charge at that point.
(E=F/Q)

Question 12

What is a non-uniform electric field?

Answer 12

An electric field with varying electric field strength throughout.

Question 13

In terms of electric field lines, what represents a stronger and weaker field?

Answer 13

Stronger - lines are closer together
Weaker - lines are further apart.

Question 14

What do 2 charged parallel plates that make an electric field look like?

Answer 14

Uniform field lines (if charge is equal) and going from the positive to negative plate?

Question 15

Why is a radial field considered a non-uniform field?

Answer 15

The electric field strength E is different depending on how far you are from a charged particle.

Question 16

What do the electric field lines around 2 point charges of opposite charge look like?

Answer 16

Describe and search it up.

https://study.com/skill/learn/how-to-draw-electric-field-lines-for-two-particles-with-equal-opposite-charges-explanation.html

Question 17

What is the equation for the electrostatic force on a charge?

Answer 17

F = EQ
E = electric field strength (N/C)
F = electrostatic force on the charge (N)
Q = charge (C)

Question 18

What is a test charge?

Answer 18

A charge with a magnitude so small that placing it at a point has a negligible affect on the field around the point.

Question 19

Is electric field strength a vector or scalar?

Answer 19

Vector (away = positive, towards = negative)

Question 20

What is the equation that finds the magnitude of the electric field strength in a UNIFORM field between 2 charges parallel plates?

Answer 20

E = V/d
E = electric field strength (V/m)
V = potential difference between the plates (V)
d = separation of plates (m)

Question 21

What are the units of electric field strength?

Answer 21

both N/C and V/m

Question 22

What are 2 facts that can be derived from the ‘field strength for a uniform field’ equation?

Answer 22

• The greater the voltage between the plates, the stronger the field
• The greater the separation between the plates, the weaker the field.

Question 23

Why can’t the equation E = V/d be used to find the electric field strength around a point charge?

Answer 23

Field around point charge is radial, so not uniform.

Question 24

What is the voltage of an earthed plate?

Answer 24

0V

Question 25

What is the derivation of the electric field strength between plates to find the work done?

Answer 25

E = F/Q = ΔV/d
Fd = ΔVQ
W = Fd
W = ΔVQ

Question 26

What does the motion of a charged particle between 2 charged parallel plates compare to?

Answer 26

It is the same as a projectile under the influence of gravity (if negative plate is at the bottom and particle is positive)

Question 27

How will a non-charged act if it projected through 2 charged parallel plates?

Answer 27

It will travel in a straight line through?

Question 28

What does the amount of deflection (of the charged particle moving through the 2 charged parallel plates) depend on?

Answer 28

mass - the greater the mass, the smaller the deflection
charge - the greater the magnitude of the charge of the particle, the greater the deflection
speed - the greater the speed of the particle, the smaller the deflection

Question 29

What is the equation for the electric field strength of a point charge?

radial field

Answer 29

E = Q/4πε₀r²

Question 30

What does the equation of the electric field strength of a point charge show?

Answer 30

• E in a radial field is not constant
• As distance from r increases, E decreases by 1/r² (when E decreases by 4, r x2)

Question 31

What is the origin of the force for electric fields?

Answer 31

Charge