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Principles of Physics
Ideal Physics World
 No energy loss
 Resistance only in
resistors
Real World
 Resistance in wires
 Resistance causes
heat
 System loses
energy

Georg Ohm experimented with various
materials
He found out that V is proportional to I in ideal
materials
VOLTAGE (V)

(I)
I = V/R → R = V/I → V = IR
V = Voltage (V)
I = Current (A)
R = Resistance (ohm = Ω)




Light bulbs are resistors
They give off light and heat
Brightness increases as current increases
Since energy is lost as light and heat more
voltage is required to have the same current
As current increases, resistance increases
because the light bulb heats up
Voltage

Current



A voltage exists across every device (voltage
supply, resistors, light bulbs, etc.)
As an electron goes through a resistor or
device it loses energy because it does work to
get through
How much energy lost per Coulomb (V)
depends on the resistance


Voltmeters are used
to measure voltage
across devices
Ammeters measure
current through
devices

A
Ammeters must be
connected in the same
path as the device
V

Voltmeters must be
connected across the
device

On all voltmeters and
ammeters there are
three ports:
Black is always
connected to the circuit
 Only one red port is
connected to the circuit

 Each port correlates to a
different scale (number
below the port is the
highest number on the
matching scale)