I've tried to create this quite simple circuit.
- V1: 1.5 v (AA battery)
- LAMP1: 1.5 v, 0.2 a (E10 incandescent light bulb)
- "Salt water": 10 ml regular water + 1 g salt
When I connect the wires together, the lamp lights up. When I connect the wires to various conductive materials (a spoon, tin foil, a penny,...), it works as well. But if I put the wires into a tiny bucket containing (salt) water, it does not.
Could you please explain why? (I guess that it is related to the water resistance/conductance but how exactly and how do I calculate it?)
Thank you.
Answer
The spoon, tin foil, and penny are all metals, and will have a very low resistance - probably well under 1 ohm, so will allow ample current to flow to light the lamp.
The salt water will have a much higher resistance, allowing very little current to flow - this low current will not be sufficient to cause the lamp to light. I just measured the resistance of some salty water - it was about 50,000 ohms (50Kohms) which would only allow 30 uA (.03 mA) to flow in your circuit - not nearly enough to light a lamp.
If you connect an ammeter in series with the lamp, you will be able to measure the current with different test materials.
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