E TEST- Resistance
Resistance
the opposition to the motion of charge through a material or device
Resistance equation
R = (theta)V / I
R
resistance (Ohms)
(theta) V
potential diff (J, C or V)
I
current (A)
What does the resistance depend on?
length, are, material, and temp
Restsnace materials
some conduct electricity better than others (less resistance)
more resistance when the material is:
hotter, longer, or thinner
What do all materials have?
some resistance
What is the thickness of a wire determined by?
the amount of current the circuit will have to supply
What are resistors used for?
to control the amount of current in a circuit
Potentiometer
variable resistor with fixed contact on one end and adjustable/sliding contact that allows the user to tap off different potential differences- dimmer switches, volume controls
Ohm's law - resistance
in many materials (including most metals) the resistance is constant over a wide range of potential differences
ohm's law- resistance equation
(theta) V = IR
What is not true for all materials?
diodes that have a small resistance or current in, on direct, and a large resistance for currents in the other directions