Chapter 22 Electric Fields

Question 1

What is the definition of electric field strength?

Answer 1

The electric field at a point in space is the force experienced per unit of positive charge at that point

Question 2

What is the equation for electric field strength?

Answer 2

E = F / Q
E = electric field strength
F = force
Q = the amount of positive charge

Question 3

How are electric fiend patterns mapped?

Answer 3

• Arrows on the lines show the direction of the field
• Electric field lines are always at 90* to the surface of the conductor
• Equally spaced lines indicate a uniform field
• Closer electric field lines represent greater electric field strength

Question 4

Is electric field strength a scalar or a vector?

Answer 4

vector, it has a direction

Question 5

What is coulombs law?

Answer 5

Any two point charges exert an electrostatic force which is proportional to the product of their charges and inversely proportional to the square of their distances

Question 6

What is the equation for coulombs law?

Answer 6

F = Qq / 4πε0r^2

Question 7

How can coulombs law be investigated?

Answer 7

Two spheres are given each the same charge
One is hung from an insulated rod and the other is held up with an insulating support on top of a balance. They are brought close together a known distance and the change in mass is calculated. And coulombs law equation is used

Question 8

What is the equation for the electric field strength for radial fields?

Answer 8

E = Q / 4πε0r^2

Question 9

Why is the equation for a radial field different?

Answer 9

Because as you move further away from a radial field the field lines spread out so the force experienced becomes reduced so the charge of the other charge does not need to be factored in.

Question 10

What is ε0?

Answer 10

It is the permittivity of free space

Question 11

What is the main difference between gravitational fields and electric fields?

Answer 11

Gravitational fields are always attractive

Question 12

What type of field is produced between parallel plates?

Answer 12

A uniform field

Question 13

What is the equation for electric fields between two parallel plates?

Answer 13

E = V / d 
E = Electric field strength
V = Potential difference
d = Distance between the two parallel plates

Question 14

How is E = V / d derived?

Answer 14

W = Fd
VQ = (EQ)d
E = V / d

Question 15

What is the equation for a parallel plate capacitor?

Answer 15

C = εA / d
C = Capacitance
ε = The relative permittivity
A = Area of plate
d = Distance between plates

Question 16

What relative permittivity?

Answer 16

This is the relative permittivity to ε0.
ε = εr x ε0
εr for a vacuum is defined as 1 because ε0 is for a vacuum

Question 17

What is the equation for the work done on an electron moving through a uniform field?

Answer 17

Work done = Ve
V = Voltage
e = Elementary charge

Question 18

What happens when a charged particle enter a uniform field perpendicular to the direction of the electric fields?

Answer 18

It moves toward the plate with the oposite charge. It follows a parabolic path

Question 19

How can the path of a charge particle in a uniform field be calculated?

Answer 19

The path can be broken down into vertical and horizontal components.

Horizontal has no acceleration so the distance moved(L) = Vt

For vertical we can use F=ma and E = F/Q
Rearranged and combined: a = EQ / m
and v = u + at can also be used
All combined is EQL / mv

Question 20

What is the area under a force distance graph equal to?

Answer 20

It is equal to the work done

Question 21

What is the are under a force distance graph equal to for two oposite charges?

Answer 21

It is equal to the work done to separate the charges

Question 22

What is electric potential?

Answer 22

It is defined as the work done per unit charge in bringing the positive charge from infinity to that point

Question 23

What is electric potential difference?

Answer 23

It is the work done per unit of charge between two points around the particle of charge

Question 24

What is the equation for the capacitance of charged spheres?

Answer 24

C = 4πε0R