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A current is charge on the move. This chapter measures it.

Three rules carry this whole chapter.

This is Chapter 11, Electricity, in your Science book.

What you will learn

  • Charge on the move. Current is charge per second.
  • Two meters. An ammeter in the path, a voltmeter across.
  • Ohm's law. V = IR, at a fixed temperature. V is the push, I the current, R the resistance.
  • What resistance depends on. Length, thickness, material.
  • Series and parallel. One path, or a path each.
  • Heating effect. H = I²Rt. H is the heat, t the time.
  • Power. P = VI = I²R = V² ÷ R. P is power.
  • The meter. It counts energy, in kilowatt-hours.

One safety rule, before anything else

Every circuit in this chapter uses a cell or a battery. Mains power, the supply at a wall socket, can kill. Only a trained electrician should touch a wall socket or its wiring.