Charge and Field Flashcards
What has an electric field?
Any charged object.
What is Coulomb’s law?
That opposing point charges will experience an attractive force, and vice versa for like point charges.
What is the force exerted on a point charge equivalent to?
kQ₁Q₂ / r² Where: k = 1/4πε (ε = permittivity of the material between the charges) Q₁Q₂ = The product of the charge on each point charge. r = the distance between the point charges
Is an attractive force between two objects negative or positive?
An attractive force between two objects is negative. A repulsive force is positive.
What is the inverse square law?
A law stating that the magnitude of a physical quantity varies inversely with the square of its distance from its source.
What is electric field strength equivalent to?
Force per unit charge.
What is the equation for the electric field strength of a linear field?
E = F/q Where: F = force q = charge on object E = field strength
Is electric field strength a vector or scalar quantity?
It is a vector - it points in the direction a positive charge would move.
What is the electric field strength of a radial field equivalent to?
E = kQ/r² Where: E = field strength Q = Charge on fixed charged r = distance of field point from charge centre
How is the inverse square law demonstrated on the field diagram of a radial electrostatic field?
By having the field lines grow further apart as they get further from the fixed charge.
What is electrical potential energy?
The work required to move a charge q from an infinite distance to a distance r away from a point charge, Q. E = kQq/r
What does a graph of electrical potential energy against distance for a repulsive field look like?
What is the form factor of a graph mapping electric potential energy against distance from the point charge?
Except for EPE not GPE.
What is electrical potential energy measured in?
Volts
What is electrical potential energy equal to?
What is electric field strength at a point in a linear field?
The electrical potential over the distance between
What is an equipotential surface?
An equipotential surface is a surface across which the electrical potential is constant.
What is Stoke’s? Law?
What is the force experienced by a sphere moving through a fluid equal to?
6πηrv
Where:
η = The viscosity of the fluid
r = radoius
Describe Milikan’s oil drop experiment.
Oil droplets were fed between two plates through an atomiser, which ionized the oil droplets via friction as they left it. The terminal velocity of a doplet could be measured, further allowing the radius of the droplets to calculated. This allowed Milikan to calculate the oil droplet’s mass. A potential difference was then created across the plates such that the oil droplet was attracted to the top plate and suspended in mid-air. The charge on the drop could then be calculated by combining F = QV/d and Stoke’s law. Milikan repeated this experiment many times and found that the charges on the droplets were always multiples of -1.6 x 10-19. This suggested that charge was quantised.
What is electrical current in terms of Q, V, and l?
I = QV/l
What is the force on a charged particle as it passes through a magnetic field?
F = Bqv
Where:
F = force on the particle
q = charge on the particle
B = magnetic field strength
v = velocity of the particle
What is the radius of the circular path of a charged particle in a magnetic field?
r = mv/Bq
Where:
r = path radius
m = particle mass
v = particle velocity
B = magnetic field strength
q = charge on the particle
How is the equation for the radius of the path of a charged particle in a magnetic field ( r = mv/Bq ) derived?
F = mv2/r
F = Bvq
⇒mv2/r = Bvq
⇒ r = mv/Bq
