Electric Feilds Flashcards
Describe the electric feild lines on a -ve charge
Acting towards -ve charge
Lines are perpendicular to the surface of a conductor
Closer the lines are the greater the electric feild
Is E a vector or scalar
Vector because it has direction, it points away from =ve and towards -ve
Define electric feild
A regional of space which a charged particle experiences a force
Define electric feild strength
The force per unit =ve charge
Define uniform field
The field strength is the same at all points
Define electric potential
The work done to move a unit of =ve charge from infinity to that point
Give 2 differences and similarities between electric and gravitational force
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
How do you derive E=V/d
W=Fd=VQ
Therfore EQd=VQ
So E=V/d
V= p.d. E=electric feild
This is only for parallel plates
Hoe do you find the permiativity of a material given the relative permiativity
Permiativity= relative permiativity X permiativity of free space
Give an equation for a weight using density
Mg=pVg
P=density
A particle is traveling parallel to to the electric feild lines, give an equation to find the velocity
Electric potential energy= kinetic energy
QV=1/2mv^2
Rearrange for v
Formulate an equation using electric feild and acceleration
EQ=F
Therfore
EQ=ma
E=V/d
VQ/d=ma
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
Vertical =
F=EQ
EQ=ma
VQ/d=ma
Horizontal=
No horizontal acceleration therfore no resultant force in horizontal therfore horizontal speed is constant
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
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)
What dos vertical deflection of an electron mean
The vertical distance it has moved due to the electric field
Define electric potential and its units
The work done to bring a unit of positive charge from infinity to that point
JC^-1 or Volts
Define potential gradient
The change in potential per unit change in distance in a given direction
What are equipotential lines
Lines to show when the potential energy is the same in the electric/ gravitational field
They always meet feild lines at right angles
How do we find the electric potential between 2 charges at a distance r
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
Give an equation for finding the electric potential between points a and b
Vtotal= Va+Vb
When do you use the electric potential equation and the E=V/d equation
Only use E=V/d for au uniform electric feild
Use other equation to find V in a non uniform feild
Give an equation in terms of charge for the electrical potential between w points simplified
V(A+B)= 1/4piE x (Qb+Qa)/r
What is the constant for energy and electrical potential
8.99 x 10^9
When do you use E=QV and the electric potential enrgy equation
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
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
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
An isolated conducting sphere is initially uncharged electrons are the transferred to the sphere
State and explain the location of the excess electrons
They are located on the surface and are equally spaced due to the repulsion
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
F=ma
Therfore only vertical force = mg
Mg=ma , g=a
The time to fall only depends on the vertical acceleration and the distance
Particles are falling between 2 parallel plates with a pd explain why the horizontal acceleration of a particle is different for each particle
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
