electric charge and fields

Question 1

what’s the triboelectric effect

Answer 1

when two objects rub against each other it can cause a transfer of electrons. This is the cause of static electricity

Question 2

what happens when an electrical charge moves close to a neutral object

Answer 2

and electrical charge is induced. the opposite charges inside the neutral object are attracted to the surface and the alike charges are repelled further into the body

Question 3

describe the process of charging by induction

Answer 3

if a conductor is earthed the earth provides positive charges. when a negative charge is brought close to the conductor a positive charge is induced. if the earth connection is removed then when the negative charge is removed the conductor will remain charged

Question 4

what happens when an electrical charge moves close to an insulator

Answer 4

the charge inside an insulator is not free to move. but if the insulator contains dipoles they will align themselves with the electric field created by the external charge. (known as polarisation)

Question 5

what is a field

Answer 5

a physical quantity that has a value at all points in space and time within a system. it can be a scalar or a vector

Question 6

rules of electric field lines

Answer 6

1. density correlates to the field strength
2. point in the direction a positive charge would move
3. never overlap
4. either end on a charge of point out towards infinity

Question 7

properties of charge

Answer 7

1. positive or negative
2. conserved
3. quantised
4. Lorentz invariant

Question 8

how are sparks produced from a pointy object

Answer 8

charge builds up at the point (minimised energy).
the point has the highest density of E-field lines. (all perpendicular to the surface)
when the E-field exceeds the dielectric strength of air it causes sparks. (coronal discharge)