Electromagnets demonstrate how putting electrical current through a coil of wire creates a temporary magnetic field. Get your junior high level students to cut an 18-inch length of AWG 16 wire. Remove ¼ inch of plastic off the ends. Starting at the top of the nail, wrap the wire around the length of a 4-inch nail, leaving 4 inches loose from the top. Wind the wire down to within ½ of the bottom of the nail, leaving 4 inches loose. Attach the ends of the wire onto the battery terminals. Scatter some iron filings on a work surface and put the nail near the filings. You see them move toward the nail and stick to it.
Get your junior high students to see the effects of series wiring. Cut two strips of wire and take ¼ inch of plastic off the ends. Put the ends of the two wires onto the terminals of a 1.5-volt battery and the opposite ends onto a 1.5-volt light bulb. The bulb glows brightly. Cut another strip of wire. Remove the wire from one of the battery terminals and put it on a second light bulb. Attach the third strip of the wire to the other terminal on the second light bulb and the opposite end onto the battery terminal. The lights both illuminate, but they are not as bright. This is because the circuit has two 1.5-volt bulbs making 3 volts, but the battery produces only 1.5 volts.
The previous experiment showed how the voltage in a series circuit became unbalanced; the battery voltage didn't match the light bulbs' voltage requirements. Use the same circuit, but remove a wire from a battery terminal. Put another 1.5-volt battery so the terminal touches the terminal you have just removed the wire from. Ensure that one of the touching terminals is positive and the other negative. Attach the wire you removed earlier onto the terminal of the second battery. Both lights will illuminate brightly. This is because the circuit requirements and the batteries have equal voltage; two 1.5-volt batteries, wired in series, make 3 volts and two 1.5-volt lights, wired in series, need 3 volts.
Parallel wiring means that every item wired has its own circuit. Use one of the batteries and the two light bulbs from the previous experiment. Disconnect all the wires. Cut another strip of wire so you have four; three from before and an extra one. Attach the ends of two of the wires to the battery terminals. Connect the opposite ends to the terminals on one of the light bulbs. The light will illuminate brightly. Attach the ends of the other two wires to the same light bulb and then attach the opposite ends to the terminals on the second light bulb. Both lights will illuminate brightly. This is because each light bulb has a direct connection to the battery and so both bulbs get 1.5 volts.