Electric Circuits

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Electric Circuits

• A circuit is a path where a current can flow
• If the flow is to be continuous, the can be no
  gaps in the path
• Intoduce gaps in the form of switches, so we can
  control completing a circuit
• Most circuits have more than one device that we
  want to provide with electrical energy

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Electric Circuits

• There are two ways to connect multiple devices to
  a voltage source
• One is called series
• The other is called parallet
• Each has unique properties which we now examine

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Series Circuits
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Series Circuits

• A single pathway through the circuit
• The current is the same everywhere in the circuit
• Each device provides resistance and total
  resistance is the sum of the devices
• Voltage divides among the devices
• Voltage drop across each device is Irdevice

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Parallel Circuits
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Parallel Circuits

• Each device connects to the voltage source
• Voltage is the same across each device
• Current from source divides into devices
• Total current is the sum of device currents
• Current in each device is just V/R
• Add devices, lower total resistance

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Circuits

• Ignore resistance of wires for calculations
• Just as we ignored air resistance
• Ohms Law answers all questions
• Lets do some sample calculations

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Series Circuit Calculation
10 ohm
20 ohm
30 ohm
12 Volt
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Parallel Circuit Calculation
10 ohm
20 ohm
30 ohm
12 Volt
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Electric Power

• Moving charges do work
• We can heat the filament in a light bulb
• We can turn the rotor in a motor
• The rate at which work is done is power
• Electric Power current x voltage
• Units are watts joules/sec amps x volts

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Electric Power
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Power Calculation
10 ohm
20 ohm
30 ohm
12 Volt
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Power Calculation
10 ohm
20 ohm
30 ohm
12 Volt
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Energy Loss in Power Lines

• Wires have some resistance
• To transport energy from Point A to Point B, we
  connect wires
• Each wire has resistance
• Energy Loss in one second is I2R
• Make I small to minimize
• Transformers convert AC Voltages

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Fuses

• Limit the current that runs through wires in your
  house
• These wires have some resistance
• Energy loss by I2R converts to heat
• Hot wires can start a fire
• Limit the current with a fuse or circuit breaker