Electricity carrying cables are often buried underground. To locate their exact position, utility workers use a tool that detects magnetic fields. Within the cables, a current of flowing charges produces a magnetic field that extends into the surrounding space. By uncovering this magnetic field, workers can locate the exact position of the unseen electric flow.
Things Required:
Two “D” cells in battery holders
Connecting wires with each end stripped 11/2 inches bare of insulation
Switch
Index card
Iron filings
Compass
Directions:
Assemble the complete circuit shown below. Place an index card on top of a section of wire so that you may not see it.
Turn the switch to the “on” position for a few minutes only. Otherwise, you will damage the cell. Lightly sprinkle iron filings onto the card. Tap the card gently. Do the filings form a pattern or do they scatter randomly? Can you explain your observations?
Turn the switch to the “off” position. Carefully return the iron filings to their container.
Place a compass alongside the wire. Note the direction that the needle points. While watching the needle, turn the switch to the “on” position. What do you observe? Explain what you see.
Suppose you switched the connectors to the cells so that their polarity might be reversed. How would that affect the direction in which the needle points? Make a guess and then find out by switching the connections. Was your guess correct?
This Is What Happens:
Electric currents produce a detectable magnetic field. The filings that fell onto the index card “felt” the force of the magnetic field. Their final position formed a pattern that followed the magnetic lines of force and this force extended outward from the wire.
Likewise, the compass needle also “felt” the magnetic force. When the current flowed, it produced a magnetic attraction that successfully competed with the Earth’s magnetic field.
