physics chapter 5 mcat

coulomb

SI unit of charge

protons

positive charge

electrons

negative charge

attractive

opposite charges have —- forces

repulsive

like charges exert —- forces

conductors

allow the free and uniform passage of electrons when charged

insulators

resist the movement of charge and will have localized areas of charge that do not distribute over the surface of the material

coulomb’s law

gives the magnitude of the electrostatic force vector between two charges. The force vector always points along the line connecting the centers of the two charges

electric field

Every charge generates one; this can exert forces on other charges. This is the ratio of the force exerted on a test charge to the magnitude of that charge

electric potential energy

the amount of work required to bring the test charge from infinitely far away to a given position in the vicinity of a source charge. Increases when two like charges move together and decreases when two opposite charges move away

potential difference

the change in electric potential that accompanies the movement of a test charge from one position to another.

positive test charge

moves spontaneously from high potential to low

negative test charge

moves spontaneously from low potential to high potential

equipotential lines

• Lines where electric potential (V) is constant

• No work is done moving a charge along the line

• Always perpendicular to electric field lines

• Closer lines = stronger field

• Used to visualize electric potential in a field

electric dipole

• Two equal but opposite charges (+q and –q) separated by a distance

• Dipole moment (p) = q × d, points from – to +

• In a uniform electric field:

  • No net force, but experiences a torque

  • Tends to align with the field

• Potential energy: U = –p·E·cosθ

diamagnetic

materials possess no unpaired electrons and are slightly repelled by a magnet

paramagnetic

possess some unpaired electrons and become weakly magnetic in an external magnetic field

ferromagnetic

possess some in[aited electrons and become strongly magnetic in an external magnetic field

lorentz force

sum of the electrostatic and magnetic forces acting on a body