Instruments that can detect or measure the flow of electricity have helped to make possible the wonders of electricity as we know them today.
Scientists in laboratories must have measuring devices for experiments leading to new uses of electricity. Power suppliers must have instruments that tell what the generating equipment is doing and to measure the amount of electricity being sold to users. Factories need instruments that keep tab on electrical equipment to make sure electricity is being used efficiently.
In fact, almost anywhere you find electric power at work you'll find electrical instruments—even in your home. The one you know best measures the amount of electricity used. Another, in the family car, shows whether the generator is charging the battery or if the battery is discharging.
What to Do
1. Make a simple kind of direct-current meter that will show you that there's a magnetic field around a wire carrying an electric current and that will detect a very tiny current.
2. Make a more refined D.C. instrument (galvanoscope) and measure the voltage of different sizes of dry batteries, and show how an electric current can be induced.
Tools and Materials You'll Need:
Pair of pliers, knife, small hammer
30 feet of No. 24 bell or magnet wire
Compass
Two coins—a penny and a dime
Fine sandpaper
Blotting paper
Plastic or cellophane tape
Wooden blocks (See Figure 4)
Glue
2 small nails
One #905 dry cell, a penlight battery, and two regular flashlight batteries
Table salt
Drinking glass
2 paper clips
Two machine bolts
How They Work
Like many electrical things, most electrical instruments depend on the action of magnetism created by an electric current. There is a magnetic field or lines of force around any wire carrying an electric current. If this field is controlled and made to react on a sensitive device, like an easily moved pointer, we have an electrical instrument.