AQA A Level Physics Electric Fields

Coulomb's Law

magnitude of force between two point charges

is proportional to the product of their charge and inversely proportional to their separation squared

the force is ATTRACTIVE with un-like charges and REPULSIVE with like charges.

Representations of electric field lines

field lines show direction of force on a point positive charge in an electric field.

lines always start/finish on a surface/charge

lines don't cross

leave surface at 90 degrees

Electric field strength, E

force acting per unit charge on a positive charge. VECTOR

Electric field strength units

N C-1 or V m-1 VECTOR

Electric potential, V, (at a point)

work done per unit charge to move a small positive charge from infinity to the point in the field

SCALAR

Units of electric potential, V

J C-1 or V (Volts) SCALAR

Electric potential, V, at infinity

Zero

Electrical Potential difference, deltaV

Work done per unit charge to move a small point positive charge between tow points in a field

SCALAR

Graphical variations of E with r (radial and uniform fields)

Radial field around positively charged hollow sphere

Uniform field

Graphical variations of V with r (radial and uniform fields)

Radial field around positively

charged hollow sphere

Uniform field

Area under graph of electric field strength against r

area under graph - electrical potential difference V

Path of charged particle in a uniform electric field

Path is parabolic, because,

Magnitude of force is constant and always in the same direction

Speed of charged particle accelerated across a potential difference, V

Loss of electrical potential energy = gain in kinetic energy

QV = 1/2 m v²

Similarities between electric and gravitational fields

field strengths are both inversely proportional to separation squared

potentials are both inversely proportional to separation

(see table on Pg 107 of Year 2 text book.)

Differences between electric and gravitational fields

masses always attract but charges may attract or repel

(see table on Pg 108 of Year 2 text book)

Accelerating charges

loss of electrical potential energy = gain in kinetic energy

Q ∆ V = 1/2mv²

Shuttling ball forces

Tension in string

force -along field line

weight downwards

Motion of electron entering uniform field perpendicular to field lines

Force acts perpendicularly to initial velocity

electron follows parabolic path

horizontal component of velocity is unaffected

Motion of electron entering uniform field in same direction as field lines

Force acts against initial velocity

therefore electron decelerates