Electric Fields - Year 13

Permittivity of free space

A measure of how easily an electric field can be created in a vacuum

Coulomb's Law

Force between two point charges is proportional to the product of their masses and inversely propotional to the square of the distance between them

An electric field

A region of space where an object with charge will experience a force

Direction of arrows on electric field lines

Direction of the force acting on a positive test charge placed into the field at that point

Electric Field Strength

Force per unit charge on a charged object at a specific point in an electric field

Path taken by charged particle moving in an electric field

Charged particle moving through an electric field will be parabolic

Radial Field

A field in which the field lines radiate out from a central point

How to work out the speed of a charged particle accelerated by an E field

Equate the work done accelerating the charged particle (QV) with the kinetic energy is gains after being accelerated

Electric field strength

The work done per unit charge in bringing a small positive test charge from infinity to a specific point in the field

Electric potential difference

The energy required to move 1C of charge between 2 points in an E-Field

Electric Field Strength from Graph

Found by determining the gradient of a graph of V vs r

Electric potential difference from a graph

Found by working out the area under a graph of E vs r

A capactior

An electrical component designed to store charge

Parallel plate capacitor

2 metal plates separated by an insulating material called a di-electric

Capacitance defined

Charge stored per unit volt

Capacitance determined from a graph

Found by working out the gradient of a graph of Q vs V

How dielectrics increase capacitance

Dielectrics contain polar molecules that align under influence of E field, reducing its strength and allowing more charge to be stored per V

Factors affecting capacitance of parallel place capacitor

Directly proportional to area and inversely proportional to place separation

How various factors are affected when a capacitor discharges

Charge, voltage and current all decrease exponentially

How various factors are affected when a capacitor charges

Charge and voltage increase to a max, but current decreases exponentially

The two factors that affect the time it takes for a capacitor to discharge in a circuit.

The resistance of the circuit and the capacitance of the capacitor

What the time constant is

Resistance x capacitance. RC

Time constant for discharging capacitor

The time it takes for the charge to fall to 1/e (or 37%) of its initial value, for a discharging capacitor

The time we consider it to take for a capacitor to discharge

5 time constants: 5RC

Time constant for a charging capacitor.

The time taken for a charging capacitor to reach 63% of the maximum charge