Conductor or Insulator?

Which materials let electricity through? Drag an object into the gap in the circuit and watch the bulb and the ammeter.

Put in the gap
In the gap
Copper wire
Its resistance
2.00 mΩ
Current
375 mA
Verdict
Conductor

The maths, live

Total resistance R = R(bulb) + R(object)R = 8 Ω + 2.00 mΩ = 8.00 Ω
Ohm's law I = V ÷ RI = 3 V ÷ 8.00 Ω = 375 mA
Bulb power P = I² × R(bulb)P = (375 mA)² × 8 Ω = 1.12 W

Drag things from the shelf into the gap, or tap them. Why does the pencil lead make the bulb dim? Does salt water conduct better than pure water?

How it works

A conductor lets electric charge flow through it easily. Metals are great conductors because they have lots of free electrons that can drift along. An insulator, like plastic, rubber, glass or dry wood, holds on to its electrons, so almost no current can flow.

Every object has a resistance (R). The bulb and the object share the battery's push, so the current is I = V ÷ (R bulb + R object). Metals add almost nothing, so the bulb is bright. Pencil lead (graphite) is a weak conductor, so the bulb is dimmer. Salt water conducts a little because the salt splits into charged particles called ions, but pure water and insulators let through only a tiny trickle.

Try this

  1. Sort all the objects into conductors and insulators. Which ones surprised you?
  2. Compare pure water with salt water. How many times bigger is the current with salt?
  3. Why does the bulb glow less with pencil lead than with copper wire?