02-06 Voltage, Current, Power - What's all this about

Water model

Voltage

Think of voltage as "water pressure".

• Voltage source V1 "pumps/raises" the pressure.
• "Water loses pressure" as it flows through the Resistive load.
• No "water" leaves the system.

Current

Think of current as the "volume of water flowing."

• High current is like "lots of water flowing"
• Current is measured in Amperes, or Amps, or A

Resistance

Think of resistance as the "pipe size"

• The higher the resistance, the smaller the pipe size, the harder it is to flow
• The lower the resistance, the bigger the pipe size, the easier it is to flow
• Resistance is measured in ohms, or Ω
• Larger units: kΩ, MΩ

Power

Think of power as the "strength of the water"

• More power means fans turn faster, water gets hotter, music gets louder
• Power is measured in Watts, or W
• Larger units: kW, MW
  • Only in HVAC and cars: also stated as horsepower, or hp
  • Only in HVAC: also stated as BTU/hr

Energy

Think of energy as "power * time"

• More energy means burnt bread, dried kettles, overdone steak
• Energy is measured in Joules, or J
• Energy is more commonly measured as Watt-hours
• Larger units: kWh, MWh
  • Only for air-conditioning: stated as BTU

Note: Power & Energy are often used interchangeably in casual conversation.

Putting it all together

Visualise:

1. Voltage at key points in the circuit
2. Current flowing through the circuit
3. Resistance of the bulb
4. Power produced by the bulb
5. Energy consumed by the bulb

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