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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)