Electric Feilds

Question 1

Describe the electric feild lines on a -ve charge

Answer 1

Acting towards -ve charge
Lines are perpendicular to the surface of a conductor
Closer the lines are the greater the electric feild

Question 2

Is E a vector or scalar

Answer 2

Vector because it has direction, it points away from =ve and towards -ve

Question 3

Define electric feild

Answer 3

A regional of space which a charged particle experiences a force

Question 4

Define electric feild strength

Answer 4

The force per unit =ve charge

Question 5

Define uniform field

Answer 5

The field strength is the same at all points

Question 6

Define electric potential

Answer 6

The work done to move a unit of =ve charge from infinity to that point

Question 7

Give 2 differences and similarities between electric and gravitational force

Answer 7

Both have infinite range , both follow an inverse square law
Gravitational force is always attractive electrostatic can be attractive and repulsive
Can not shield gravitational force, however electrostatic force is effected by materials

Question 8

How do you derive E=V/d

Answer 8

W=Fd=VQ
Therfore EQd=VQ
So E=V/d
V= p.d. E=electric feild
This is only for parallel plates

Question 9

Hoe do you find the permiativity of a material given the relative permiativity

Answer 9

Permiativity= relative permiativity X permiativity of free space

Question 10

Give an equation for a weight using density

Answer 10

Mg=pVg
P=density

Question 11

A particle is traveling parallel to to the electric feild lines, give an equation to find the velocity

Answer 11

Electric potential energy= kinetic energy
QV=1/2mv^2
Rearrange for v

Question 12

Formulate an equation using electric feild and acceleration

Answer 12

EQ=F
Therfore
EQ=ma
E=V/d
VQ/d=ma

Question 13

An electron is fired with only horizontal velocity perpendicular to the feild lines between 2 oppositely charged plates give an equation for the vertical force of the e- and describe the horizontal force

Answer 13

Vertical =
F=EQ
EQ=ma
VQ/d=ma

Horizontal=
No horizontal acceleration therfore no resultant force in horizontal therfore horizontal speed is constant

Question 14

How can you fi d the final velocity and the direction n of an e- fired perpendicular to the feild lines between 2 oppositely charged p[lates, given the horizontal and perpendicular distance between plates and the p.d, and initial horizontal speed

Answer 14

Use s=vt to find t as it is constant in horizontal and vertical
Then use VQ/d=ma to find the acceleration of electron
Then use Suvat to find the vertical final speed
Now you have how and vertical speed so find the resultant final speed and use trig for the direction (angle)

Question 15

What dos vertical deflection of an electron mean

Answer 15

The vertical distance it has moved due to the electric field

Question 16

Define electric potential and its units

Answer 16

The work done to bring a unit of positive charge from infinity to that point
JC^-1 or Volts

Question 17

Define potential gradient

Answer 17

The change in potential per unit change in distance in a given direction

Question 18

What are equipotential lines

Answer 18

Lines to show when the potential energy is the same in the electric/ gravitational field
They always meet feild lines at right angles

Question 19

How do we find the electric potential between 2 charges at a distance r

Answer 19

Find the electric potential for each charge up to that point where r= half the distance from the 2 charges (distance to midpoint)
Now do the same for the other charge
Add these two together as electric potential is a scaler quantity so we do not have to worry about direction

Question 20

Give an equation for finding the electric potential between points a and b

Answer 20

Vtotal= Va+Vb

Question 21

When do you use the electric potential equation and the E=V/d equation

Answer 21

Only use E=V/d for au uniform electric feild
Use other equation to find V in a non uniform feild

Question 22

Give an equation in terms of charge for the electrical potential between w points simplified

Answer 22

V(A+B)= 1/4piE x (Qb+Qa)/r

Question 23

What is the constant for energy and electrical potential

Answer 23

8.99 x 10^9

Question 24

When do you use E=QV and the electric potential enrgy equation

Answer 24

Use E+QV when you are finding the energy at a point as no work is being done as r is constant
When you are find the electric potential energy between points, work is being done to move those charges to that point therfore use the potential equation

Question 25

An electric feild acts into the plane of a paper an electron enters the feild at 90 degrees to the feild lines what direction is the force not the electron compared to the direction of the feild

Answer 25

The direction of the force on the electron is always in the opposite direction to the direction of the electric feild regardless of the angle

Question 26

An isolated conducting sphere is initially uncharged electrons are the transferred to the sphere
State and explain the location of the excess electrons

Answer 26

They are located on the surface and are equally spaced due to the repulsion

Question 27

Particles are falling vertically between 2 parallel plates with a potential difference , explain why the time to fall vertically os independent of the mass of a particle

Answer 27

F=ma
Therfore only vertical force = mg
Mg=ma , g=a
The time to fall only depends on the vertical acceleration and the distance

Question 28

Particles are falling between 2 parallel plates with a pd explain why the horizontal acceleration of a particle is different for each particle

Answer 28

Mass is not constant since the particles masses will vary
Charge on a particle is not constant as a=Eq/m , E is constant however m and q are not therfore acceleration will also vary