Datasheet-1

Project 26

Double Switching Ammeter

This project is similar to the preceding one, but measures current instead

of voltage. Build the circuit, and set the meter (M5) to the 1A setting. The

lamps (L4) are on dimly and the meter measures the current through the

circuit. Push the press switch (S2) to turn off the bottom lamp. Turn on

the slide switch (S1) to turn off the middle lamp. Compare the current

with one, two, or all three lamps on. Disconnect the battery holder when

you are finished with this project.

This circuit is an example of how current

decreases as parts are added in series. If

more than one lamp is on, the voltage

from the batteries is split among them, and

less current will flow through the circuit.

In theory the current with one lamp on

should be twice as much as when two

lamps are on and triple as much as when

three lamps are on, but your results will be

different because incandescent lamps like

these have more resistance when they are

brighter, and because your M5 meter is a

simple meter with limited accuracy.

With all three lamps on (both switches off), what is the current?

Turn on one or both switches, and compare the current measured with

one, two, or all three lamps on.

Why did the current change?

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