Electromagnetism - Electrostatics

Question 1

How do objects ‘charge up’?

Answer 1

Two items rub together
Electrons will move from one to the other, depending on the location on the triboelectric series
A low affinity for electrons means that the material is likely to pass electrons to the other material, becoming postively charged
A high affinity for electrons for electrons means the material is likely to accept electrons form other materials, becoming negatively charged

Question 2

Static Discharge - Law of Distribution of Charge

Answer 2

• The net amount of charge produced in any transfer process is zero
• Charges cannot be created or destroyed, just transferred

Question 3

Coulombs Law

Answer 3

What if the charged object do not touch?
Equal and opposite forces act on the charges, defined by:
F = kQq/r
A positive force denotes an repulsive force
A negative force denotes an attractive force

Question 4

Electric Fields

Answer 4

Field lines show the direction in which a positive charge will travel
More field lines means a larger E field
Field lines can be though of as net forces
(In Electric fields, negative lines point inwards, positive outwards)

Question 5

Uniform Fields

Answer 5

A charge will accelerate in a uniform field (coloumbs law)

Question 6

Strength of E (Electric field)

Answer 6

E= F/Q
where E is the strength, f is electic force (coloumbs law) and q is charge
F = ma
F = qE

Question 7

Electric Potential

Answer 7

Work per unit charge (J/C) required to move a point charge from infinty to a known position (x)

Question 8

EP Equation

Answer 8

V = change in U/q
V = W/q
Electric potential is also called potential difference
E field = V (potential difference in volts) / d (in m)

Question 9

Work done on/ by E field

Answer 9

+ - with the field lines - decrease negative change in potential - negative decrease change in potential energy (U) - work done by E field
+ - against the field lines - positive increase change in potential - positive increase change in potential energy (U) - work done on E field
- - with the field lines - positive increase change in potential - positive increase change in potential energy (U) - work done on E field
- - against the field lines - negative decrease change in potential - negative decrease change in potential energy (U) - work done by E field