Agenda Bell Work

• Van der Graaf

• Notes: Ohm’s Law• Practice WS

• Static vs. Current Electricity Quiz tomorrow

1. What parts are in a simple circuit? How is it set up?

2. What is voltage?3. What is ampere?

4. How do these two relate to each other in a circuit?

Resistance and Ohm’s Resistance and Ohm’s LawLaw

November 15, 2012November 15, 2012

ObjectivesObjectives

1.1. Describe the parts of Ohm’s LawDescribe the parts of Ohm’s Law- Volts, amps, and resistanceVolts, amps, and resistance

2.2. Given two known values, calculate Given two known values, calculate the unknown using Ohm’s Lawthe unknown using Ohm’s Law

Ohm’s LawOhm’s Law

Relationship between current, Relationship between current, resistance, and voltageresistance, and voltage

Electrical ResistanceElectrical Resistance

Resistance of Resistance of electrons to flow in electrons to flow in a circuita circuit

What affects What affects resistance?resistance?

• Length, and width Length, and width and type of wireand type of wire

Shown by a zig-zag Shown by a zig-zag symbol in a circuitsymbol in a circuit

Controls currentControls current

Measured in ohmsMeasured in ohms

Ohm’s LawOhm’s Law

Current is proportional to the voltage Current is proportional to the voltage and inverse to the resistanceand inverse to the resistance

Current(I) = Voltage/ResistanceCurrent(I) = Voltage/Resistance

Units:Units:• Amperes = volts/ohmsAmperes = volts/ohms

1 volt across a circuit with a resistance of 1 volt across a circuit with a resistance of 1 ohm produces a current of 1 ampere1 ohm produces a current of 1 ampere

What is the current if there are 12 volts What is the current if there are 12 volts across the same circuit?across the same circuit?

What about If the resistance increased to What about If the resistance increased to two ohms with 1 volt?two ohms with 1 volt?

How much current flows through a How much current flows through a lamp with a resistance of 60 ohms lamp with a resistance of 60 ohms when the voltage across the lamp is when the voltage across the lamp is 12V?12V?

What is the resistance of an electric What is the resistance of an electric frying pan that draws a current of frying pan that draws a current of 12A when connected to a 120-V 12A when connected to a 120-V circuit?circuit?

Electric Shock and Ohm’sElectric Shock and Ohm’s

Result from the current through the Result from the current through the bodybody

Depends on voltage and body’s Depends on voltage and body’s electrical resistance (100 ohms to electrical resistance (100 ohms to 500,000 ohms)500,000 ohms)

Effect of Electric Current on the Effect of Electric Current on the BodyBody

Current(A)Current(A) EffectEffect

0.0010.001 Can be felt`Can be felt`

0.0050.005 Is painfulIs painful

0.0100.010 Causes involuntary muscle Causes involuntary muscle contractions (spasms)contractions (spasms)

0.0150.015 Causes loss of muscle controlCauses loss of muscle control

0.0700.070 Goes through the heart, serious Goes through the heart, serious damage, probably fatal if lasts damage, probably fatal if lasts longer than 1slonger than 1s

At 100,000 ohms how much current will At 100,000 ohms how much current will flow through your body if you touch the flow through your body if you touch the terminals of a 12-V battery?terminals of a 12-V battery?

If your skin is very moist, so that your If your skin is very moist, so that your resistance is only 1000 ohms, and you resistance is only 1000 ohms, and you touch the terminals of a 12-V battery, touch the terminals of a 12-V battery, how much current do you receive?how much current do you receive?

To receive a shock there must be a To receive a shock there must be a difference in voltage ( a circuit must difference in voltage ( a circuit must be formed)be formed)

Electron flow will follow the path of Electron flow will follow the path of least resistanceleast resistance

Plugs and socketsPlugs and sockets

Wired with three connectionsWired with three connections

Two flat prongs are for current-Two flat prongs are for current-carryingcarrying

The larger round prong connects to a The larger round prong connects to a wire in the ground (grounded)wire in the ground (grounded)