Ohms Law

Ohm’s Law Mitsuko J. Osugi Physics 409D Winter 2004 UBC Physics Outreach

Ohm’s Law ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Current and Voltage Defined ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Think of voltage as what pushes the electrons along in the circuit, and current as a group of electrons that are constantly trying to reach a state of equilibrium .

Ohmic Resistors ,[object Object],[object Object],[object Object],[object Object]

Voltage and Current Relationship for Linear Resistors Voltage and current are linear when resistance is held constant.

Ohm’s Law continued ,[object Object],[object Object],[object Object]

Kirchhoff’s Current Law ,[object Object],The amount of current that enters a junction is equivalent to the amount of current that leaves the junction

Kirchhoff’s Voltage Law ,[object Object],Sum of all voltage rises and voltage drops in a circuit (a closed loop) equals zero

Series Circuit ,[object Object],[object Object],[object Object]

Parallel Circuit ,[object Object],[object Object],[object Object]

[object Object],[object Object]

The Light Bulb and its Components ,[object Object],[object Object],[object Object],[object Object]

Light bulbs and Power ,[object Object],[object Object],[object Object],[object Object]

Bulbs in series experiment ,[object Object],[object Object],[object Object]

Bulbs in series experiment continued…

Bulbs in parallel experiment ,[object Object],[object Object],[object Object]

Bulbs in parallel experiment continued…

Light bulbs are not linear ,[object Object],The filaments of light bulbs are made of Tungsten, which is a very good conductor. It heats up easily.

As light bulbs warm up, their resistance increases. If the current through them remains constant: ,[object Object],[object Object],[object Object],[object Object]

Voltage versus Current for Constant Resistance The light bulb does not have a linear relationship. The resistance of the bulb increases as the temperature of the bulb increases.

“ Memory Bulbs” Experiment ,[object Object],[object Object],[object Object]

“ Memory Bulbs” Continued… ,[object Object],[object Object],[object Object],How did THAT happen?? Temperature of bulbs increases  resistance increases  power dissipation (brightness) of bulbs increases

Conclusion ,[object Object],[object Object],[object Object],[object Object],[object Object]

You’re turn to do some experiments! ,[object Object]

The equipment you’ll be using: ,[object Object],[object Object],[object Object],[object Object],[object Object]

How to use a voltmeter: ,[object Object],[object Object],[object Object],[object Object]

Measuring Voltage Voltage: Probes connect to either side of the resistor

Breadboards ,[object Object],The breadboard How the holes on the top of the board are connected:

Series Resistors are connected such that the current can only take one path

Parallel Resistors are connected such that the current can take multiple paths

Real data ,[object Object],[object Object],[object Object]

Ohms Law

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Ohms Law