MEPX
Chapter 7 of 12All chapters
  1. 1What engineers do
  2. 2The design process
  3. 3Forces and loads
  4. 4Stress, strain and materials
  5. 5Structures
  6. 6Mechanisms
  7. 7Electrical basics
  8. 8Energy in machines
  9. 9Manufacturing and tolerances
  10. 10Safety factors and failure
  11. 11Testing and standards
  12. 12Responsibility

Chapter 7 of 12

Electrical basics

Circuits, Ohm and power.

The three quantities

Voltage is the push, current is the flow, and resistance opposes it. Ohm's law ties them together: voltage equals current times resistance, written V = I R.

  • Power is voltage times current, in watts, and turns into heat in a resistance.
  • In series components share the current; in parallel they share the voltage.

Practical consequences

Thin wire has more resistance, so it heats up, which is why cable size is matched to current. Long runs lose voltage, which is why power is transmitted at high voltage and low current.