22, Electric Fields Flashcards
What is a field?
A region where an object will experience force at a distance (due to some property of the object).
What does the equation E = F/Q show?
Electric field strength at a point = force experienced per positive charge.
How would you draw the electric field lines between a positively and negatively charged sphere?
Lines leave the positive sphere and bend towards the negative one, arrows point from positive to negative, and leave/enter the sphere’s at 90 degree’s to the surface.
State Coulomb’s law.
Any two point charges exert an electrostatic force on each other that is directly proportional the the product of their charges and inversely proportional to the square of the distance between them.
How can you investigate Coulomb’s law?
Attach two charges onto insulating rods, place one on a top-pan balance, the change in “weight” shows the change in force being applied between the two spheres.
What does the equation E = V/d mean?
In a uniform field, electric field strength = P.D. across plates / distance between plates.
How do you use the relative permittivity to find the actual permittivity?
ε = ε_r * ε_0 or permittivity = relative permittivity * permittivity of free space.
How did Millikan show that charge is quantised?
He used ionising x-ray’s to give oil droplets charge, he suspended these droplets between two charged plates and used the force needed to keep them stationary to find the charge of the droplets, he found that the charges came in integer multiples of e.
How can you predict the trajectory of a charged particle travelling through a uniform electric field?
Suvat equations, similar method to projectiles.
How is the equation E = Qq/(4pi ε_0 r) derived?
Integrating a force-separation graph of two charged particles, (equation given by F = Qq/(4pi ε_0 r^2)), it assumes the inside of the sphere is a vacuum, other permittivity values can be used.
What does the equation C = 4pi ε_0 R mean and where does it come from?
It is the capacitance of a charged sphere from combining C = Q/V and V = Q /(4pi ε_0 r).
Define electric potential.
The potential at a point is defined as the work done per unit charge in bringing a positive charge from infinity to that point.
What is an equipotential?
These are the lines upon which every point has equal potential, e.g. for a charged sphere the equipotential form several circles with increasing gaps between them.
