The ammeter that never changes

By the end you can say what a lamp actually takes from a circuit — and it is not current.

A very common way to think about this

“The lamp uses up current, so less comes back out of it than went in.”

Everything else we plug in gets consumed — fuel, water, batteries. The lamp is obviously taking something, and current is the only thing we have a name for yet.

1. Predict first

Before you move anything: the ammeter reads 148 mA just BEFORE the lamp. What will it read just AFTER the lamp?

2. Try it

Where you clip the ammeter — The reading is identical at all four points, so nothing was removed in between.
Lamp resistance (10–100 ohm) — Changing the lamp changes the reading everywhere at once, never at one point only.

One meter, four clip points. Move it and read again.

Ammeter148.5 mA

Atbefore the lamp

Lamp40.0 ohm

Clip the ammeter here

Lamp resistance40 ohm

3. The check

Keep experimenting above. This question opens once you have seen the thing it asks about.

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