To build a model that illustrates electric current.
4 D-cells (1.5 volt)
D-cell battery holder
3 alligator clip leads
2 bulbs and bulb holders
While we can float on a raft gliding dow n the Mississippi or ride in cars moving in traffic, nobody can see electric current flow. Even in the case of lightning, we are seeing the flash of hot glowing gases produced by electric current--not the current itself. However, we can infer the presence of electric current using light bulbs and magnetic compasses in much the same way as a flag indicates the presence of wind. In this activity, you will build a model
to study electric current.
PART A: WHAT IS HAPPENING IN THE WIRES?
Step 1: With the circuit arranged as shown in Figure A,
turn the bulbs on and off by connecting and disconnecting one of the wires.
Observe the wires when the circuit is closed
1. Is there any visual evidence that something is moving around the
circuit when the bulbs are lit? For example, does one bulb light
before the other? Does one bulb go out before the other? Is one
bulb brighter than the other?
Position a compass underneath the wire
Step 2: Place a magnetic compass on the table near the circuit with the needle pointing to the "N". With the bulbs unlit, place one of the wires on top of the compass parallel to the needle as in Figure B. Connect and disconnect a lead in the circuit several times while you observe the compass needle. Observe what happens to the needle when the bulb lights. Observe what happens
to the needle when the bulbs go out.
Step 3: Place the compass beneath the wire in different parts of the circuit. Be sure the needle is parallel to the wire when the bulbs are not lit. Observe
the needle as you open and close the circuit several times. Look to see if the needle deflects in the same direction as before. Look to see if the amount of the
needle's deflection is the same as before. Also observe whether the bulbs must be lit to deflect the compass needle.
2. What evidence supports the notion that something is happening in the wires while the bulbs are energized?
3. What evidence supports the notion that whatever is happening occur s uniformly in all parts of the circuit?
PART B: Is There Directionality To What Is Happening In The Circuit?
Step 4: Arrange the circuit as in Figure A. Place one of the wires on top of
the compass parallel to the needle. Open the circuit while you carefully
observe the needle. Note whether the needle deflects clockwise or
Step 5: Reverse the leads from the battery without altering the circuit and
compass. Do this by simply exchanging the lead connected to the positive
terminal of the battery with the lead connected to the negative terminal.
Open and close the circuit while you watch the compass needle. Watch the
needle deflect and note whether it is clockwise or counterclockwise.
4. Is the direction of the deflection the same as in Step 4, before the leads to the
battery were reversed? Is the amount of the needle's deflection the same as before?
5. Suppose something is flowing in the wires. Do you think the direction the needle is deflected is caused by the amount of the flow or the direction of the flow?
Step 6: Remove one of the D-cells from the battery holder so that the
battery holder only has two cells instead of three. Carefully observe
the deflectionof the needle while you repeat Steps 4 and 5.
6. How do the size and direction of the compass needle's deflections compare when you use two cells instead of three?
Step 7: Install two more D-cells in the battery holder so that it has four D-cells. Carefully observe the deflection of the needle as you repeat Steps 4 and 5.
7. How do the deflections of the compass needle compare to those with two and
three D-cells? Do you think the size of the needle's deflection is caused by amount of the flow or the direction of the flow?
8. Hypothesize what is happening in the circuit when bulbs are lit compared t o when they are not.
9. Hypothesize what is happening in the circuit when the direction of the compass deflection reverses.
10. Hypothesize what is happening in the wires when the amount of the needle's
11. What do you think the battery does?