OHM’S LAWPrinciples of Physics

Ideal Circuits

Ideal Physics World No energy loss Resistance only in

resistors

Real World Resistance in

wires Resistance causes

heat System loses

energy

Ohm’s law

Georg Ohm experimented with various materials

He found out that V is proportional to I in ideal materials

(I)

V

OLT

AG

E (

V)

Ohm’s Law

I = V/R → R = V/I → V = IR V = Voltage (V)I = Current (A)R = Resistance (ohm

= Ω)

Light Bulbs 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

Volt

ag

eCurrent

Voltage Loss in Resistors

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

Measuring Voltage and Current

Voltmeters are used to measure voltage across devices

Ammeters measure current through devices

Measuring Voltage and Current

A

V

Ammeters must be connected in the same path as the device

Voltmeters must be connected across the device

Measuring Voltage and Current 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)