- Charge is a physical property of matter
- Both positive and negative charge exists
- When two bodies with a net electrical charge come together, they experience a force
- The SI unit for charge is the Coulomb (C)
Not in the course, but
FIf F is positive, the force is repulsion; if it is negative, it is attraction.
Note the similarity with Newton’s Law of Gravitation.
- Electric charge produces electric fields
- The electric field is a vector – has both magnitude and direction
- Represented by lines of force with arrows
- These represent the direction that a positive charge would move in if it were placed in that location
Electrical field strength
Measured in N/C or V/m
E = F / q
Note that E is electrical field strength not energy.
- To move charges, we need to do work
- E.g. when two positive charges are put together
- This work is stored as electrical potential energy
W = Vq = Fd
Where V = voltage, q = charge, d = distance moved, F = force applied
Note that 1 V gives a particle with 1 C of charge 1 J of electrical potential.
Electrical field between parallel plates
- Between these plates is a potential difference
- There is a uniform electric field across the plates
E = V / d
E = electrical field strength, V = voltage across the plates, d = distance between them