Resistance and Ohm’s Law

Current Electricity and Static Electricity

Current Electricity Static Electricity amount of charge moving through a

circuitbuild up of charged particles in one

spotIn a conductor In an insulatorMoving Charge Non-moving Charge

What about a battery: Electrical energy does not move through a battery so does this mean it is static: No because the charge will move as soon as you allow it

Resistance

• Resistance: The ability of a substance to slow down the flow of electrons

Resistance

• Resistance: The ability of a substance to slow down the flow of electrons

What does this look like: Traffic moving from three lanes to one lane. Cars move fast in three lanes but when they have to merge into one lane their speed slows down

Amount of Resistance in different parts of the circuit

1) Wire: electrons move easily through the conducting wire (that is why we use copper for wires)

= Almost no energy is lost = Almost no resistance

2) Electric load:

Amount of Resistance in different parts of the circuit

1) Wire: electrons move easily through the conducting wire (that is why we use copper for wires)

= Almost no energy is lost = Almost no resistance

2) Electric load: Light bulbs and heaters force the electrons to move into a narrow space which slows them down.

= Lots of energy is lost as heat or light = high resistance

Energy lost in heater or light

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Resistance and CurrentMeasurements and (units):Voltage (Potential Energy): measured volts (v)Current: measured in amps (A)Resistance: measured in ohms (Ω)

OHM`S LAW

Resistance and Current

Measurements and (units):Voltage (Potential Energy): measured volts (v)Current: measured in amps (A)Resistance: measured in ohms (Ω)

OHM`S LAWMeasuring the amount of current that a given voltage produces

Ohm was able to calculate the resistance of a circuit

Electrical Resistance=ratio of voltage to currentVolts (V):Current (A)

Measuring Resistance Using Ohms Law

R(resistance) = V (voltage) OR V = IR OR I = V I (Current) REg. A 3.0 Volt battery attached to a circuit gives off

0.75A. What is the resistance in this circuit?

Measuring Resistance Using Ohms Law

R(resistance) = V (voltage) OR V = IR I (Current)Eg. A 3.0 Volt battery attached to a circuit gives

off 0.75A. What is the resistance in this circuit?

R = V = 3.0V = 4.0 Ω I 0.75A

Questions

1) The current through a load in a circuit is 2 A. The potential difference (voltage) across the load is 12V. What is the resistance.

R = V/I = 12V/2A =6Ω

2) The resistance of a car headlight is 12 Ω. If there is a current of 3 A through the headlight. Find the voltage across the headlight.

V = IR = (3A)(12Ω) =36V

3) A 12.0V potential difference is measured across a load that has a resistance of 6 Ω. What is the current through this load

I = V/R = (12.0V)/(6Ω) = 2A