Resistance How much energy does it take to push a coulomb of charge across a filament? Defined as the ratio of POTENTIAL DIFFERENCE across the LOAD POTENTIAL.

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Presentation transcript:

Resistance How much energy does it take to push a coulomb of charge across a filament? Defined as the ratio of POTENTIAL DIFFERENCE across the LOAD POTENTIAL DIFFERENCE = VOLTAGE (V) LOAD = CURRENT (I) V R = --- I Voltage Resistance = ------- Current

Units of Resistance Units of Resistance are called OHMS Named in honour of Georg Simon Ohm The symbol for Ohms is the greek letter OMEGA (Ω) Ohm was the first to publish results of various resistances on types of wires

Georg Ohm’s Findings Ohm took various types of conductors Applied a current across the wire No matter what the Potential Difference (Voltage) --- the Resistance was the same Called Ohm’s Law

Ohm’s Law V = IR Voltage = Current x Resistance http://www.mhhe.com/physsci/physical/giambattista/circuits/circuits.html http://www.riedon.com/riedon_calculator.htm

Model Problem What is the resistance of the heating coil of an electric heater if a current of 12.5 A runs through it? I = 12.5 A V = 120 V R = V / I R = 120 / 12.5 R = 9.6 V / A R = 9.6 Ω

Wasting Energy Do resistors have to convert energy to a different source? Can be used to control the current or Potential difference at different points in the circuit.

Measuring Resistance What is the Resistance? R = V / I V = 6 I = 3 3 Amps Potential Difference = 6