Electric Field and Potential

Study Notes

Electric field behaves as if all the charge creating it is at a point in the centre of the sphere when observed from outside.
Electric potential is defined as the work done in bringing a test unit positive charge from infinity to a point in the electric field.
The potential of a charge at infinity is always defined to be zero.
If the charge creating the field is positive, work must be done to bring a test positive charge in from infinity, as like charges repel.
If the charge creating the field is negative, the work done to bring in a test positive charge from infinity is negative, as unlike charges attract.

Electric field strength varies with distance for a point charge, a capacitor, and a hollow charged sphere.
Negatively charged point charges and spheres would give negative versions of the same graph.
The potential due to a positive charge is positive, while the potential due to a negative charge is negative.

Electric field strength declines with distance following an inverse square law (E ∝ 1/r²).
Electric potential is a measure of the potential energy per unit charge.
Potential energy on a charge due to a potential V is: P.E. = qV.

Field theory is a model for explaining forces that act at a distance, such as electric, magnetic, or gravitational forces.
Electric fields are used to explain the forces that act between charges.
Forces on charges can be represented by drawing field lines (lines with arrows).
The closer together the lines are, the stronger the field.
Field lines point in the direction a positive test charge would move.

There are two types of charge: positive charge (carried by particles such as protons) and negative charge (carried by particles such as electrons).
The unit of charge is the coulomb (C).
Charge comes in discrete packets, and it is quantized.
The smallest unit of charge is 1.6 × 10⁻¹⁹C, the size of the charge on an electron or proton.
Any object carrying a charge will experience a force when in the presence of another body also carrying a charge, following Coulomb's Law.
Like charges repel, while unlike charges attract.