yr 2 - electrical fields

What does the direction of the field lines represent?

The direction of the force acting on a positive test charge

Electrical field strength??

• Force / unit charge

  • Or also E=kq/r²

  • Where k= 9×10⁹

Coulomb’s law ?

• The product of the two charges is directly proportional to the force of attraction/repulsion but inversely proportional to the square of the distance between them

  • F = kQ1Q2 /r²

Electrical potential ?

The work done to take a positive test charge from infinity to a point

• V= wd/q

Electrical potential in a radial field??

Here we use V= kQ/r

• we add in the sign of the charge here

Field line properties?

• Parallel and evenly spaced (uniform)

• the concentration across the field lines is equal

• goes from + to -

• acceleration of electrons in the field is equal

• on a positive test charge the direction of the force is outwards

Equipotential surface?

Point at which zero work is done to overcome to force of attraction/#

follows the shape of the plates and should be perpendicular to the field lines

Electric potential in parallel plates?

w = f x d and E = f/q so if f = qe then w= qe x d, we know w/q is V so V= Ed and therefore V/d is the potential

• We only use this in parallel plates NOT radial fields

Electric field strength in a radial field?

E =kq/r²

Acceleration of a particle in an electric field?

• f =ma and f =qe so ma=qe , ma =qv/d so a = qv/md

• we use e=v/d as it applies to moving particles in parallel plates

Potential difference?

Work done per unit charge

Will the acceleration of many electrons in an electric field between two plates be the same?

YES!!

Following a=qv/md , all values for the electrons are the same

Will the acceleration of an electron and a proton be the same in an electric field between two plates?

NO!!

Following a=qv/md, the variable which is different is m as a proton is heavier than an electron