Electric Fields

Question 1

Field Lines

Answer 1

• An electric field is defined as a region where a charged particle exerts a force, it is shown with field lines
• The closer the lines are drawn together, the stronger the field they represent is
• direction of lines = direction a positive test charge would move

Question 2

How to find field lines

Answer 2

• place a test compass at a point around the magnet
• draw a dot where the compass needle points
• place the compass on that point and repeat
• connect all the dots into one field line

Question 3

Electric Field Strength

Answer 3

• Force = Electric Field Strength*charge
• E is a vector, and is in the same direction as the force acting on a positive charge
• charge on an electron = -1.6*10^-19

Question 4

Uniform Fields

Answer 4

• Occurs in parallel and oppositely charged plates
• Field lines are all parallel and evenly spaced , so force is equal at all points
• slight curving of lines at the edges of the plates
• Electric field strength = Potential difference between plates/distance

Question 5

Radial fields

Answer 5

• field lines spread out over distance so field strength decreases
• can be produced by a point charge
• Electric Field strength = k*(charge/distance^2)
• k= 8.99*10^9
• electric potential in a radial field = k *(Q/r)

Question 6

Equipotential Lines

Answer 6

• perpendicular to the field lines in uniform, concentric circles in radial fields
• Moving along them requires no work to be done against the field, work is done when moving between them
• work done against field= charge*difference in potential between equipotential lines

Question 7

Uses of electrostatics

Answer 7

• Microwaves oscillate water molecules in an alternating field so that food heats up
• LCD’s use electric fields to rotate polarising lenses and let light in
• cropspraying/electrostatic precipitators give particles a negative charge and what needs to be sprayed a positive charge
• photocopiers let light leak the charge away in the shape of the image, then ink attaches to the positive parts and paper is stuck to it to print the image onto the paper

Question 8

Coulombs law

Answer 8

F = k(charge on object 1charge on object 2/distance^2)

Question 9

Potential

Answer 9

• electric potential = the work done in bringing a positive charge from infinity to that point
• is positive for positive charges, negative for negative charges
• Electric Potential Energy = charge*potential energy
• E.P.E increases when moving to a higher potential, decreases when moving to lower
• electric field strength is the gradient of the change in electric potential over distance, as it the field lines point from areas of high potential to low potential, so the greater the difference the steeper the negative gradient of the field line