Electric fields

Question 1

Electric field strength

Answer 1

the force experienced per unit positive charge at that point in space
E=F/Q

Question 2

Electric field lines

Answer 2

Arrow on an electric field show direction of field - they show the direction positive charge will be pulled
Lines are always at right angles to the surface of a conductor
Closer lines represent greater electric field strength and equally spaced parallel lines represent uniform field

Question 3

Coulomb’s law

Answer 3

Any two point charges exert an electrostatic force on each other that is directly proportional to the product of their charges and inversely proportional to the square of the distance between them
F=K Qq/r^2
K= 1/4piƐ0 where Ɛ0 is 8.85 x10^-10

F= Qq/(4piƐ0r^2)

Question 4

Electric field strength between parallel plates (equation and derrivation)

Answer 4

W=Fd
W=QV and F=EQ
QV =(EQ)d
E=V/d

Question 5

Capacitance between parallel plates

Answer 5

C is proportional to A/d
C= ƐA/d
where Ɛ is Ɛ0Ɛr

Question 6

Milikan oil drop experiment

Answer 6

Oil droplets are charged with a small electric charge and allowed to fall under gravity in a vertical uniform electric field
The voltage can be changed to adjust the force
When the air drop hovers mid-air, mg =EQ=VQ/v
Q=ne where n is the elementary charge
V = mgd/ne and only certain values of voltage will be measured as n must be an integer

Question 7

work done on electron in uniform electric field

Answer 7

E= V/d
F=EQ
W=Fd=EQd
W=Vq=Ve

Question 8

Electric potential energy

Answer 8

the total work done to bring the particles from infinity to a separation
energy =Qq/4piƐ0r

Question 9

Electric potential

Answer 9

The work done per unit charge in bringing a positive charge from infinity to that point
V =E/q = Q/4piƐ0r

Question 10

Electrical potential difference

Answer 10

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

Question 11

Capacitance of isolated sphere

Answer 11

C=Q/V
= 4piƐ0rV/V
=4piƐ0r