12 Electric current Flashcards
charge carriers
charged particles that move through a substance when a pd is applied across it
potential difference
work done or energy transfer per unit charge between two points when charge moves from one point to another
V = W/Q
resistance
pd / current
ohm’s law
the pd across a metallic conductor is proportional to the current, provided the physical conditions do not change
resistivity
resistance per unit length x area of cross-section
superconductor
a material that has zero electrical resistance
critical temperature a superconducting material
temperature at and below which its resistively is zero
light-dependent resistor
resistor which is designed to have a resistance that changes with light intensity
postive temperature coefficient
the resistance of a metal increases when its temperature is increased
negative temperature coefficient
the resistance of a semiconductor increases when its temperature is increased
current equation
∆Q = I∆t
emf of a source of electricity
as the electrical energy produced per unit charge passing through the source
work done
W=IV∆t
electrical power
P=IV
resistance equation
R=V/I
resistivity equation
p = RA /L
diode
only let the current go one way (0.6v)
electric current
rate of flow of charge
I= Q/t
potential difference
work done per unit charge
V=W/Q
unless stated in questions ammeters and voltmeters should be treated as ideal
zero and infinite resistance respectively
negative coefficient
A negative coefficient for a material means that its resistance decreases with an increase in temperature. Semiconductor materials (carbon, silicon, germanium) typically have negative temperature coefficients of resistance.
