AY Honors/Electricity/Answer Key
Electricity
Explain and illustrate an experiment by which the laws of electrical attraction and repulsion are shown.
Explain the difference between direct and alternating current, and demonstrate the uses to which each is adapted. Give a method of determining which kind flows in a given circuit.
Electricity in a direct current (DC) circuit flows in only one direction. In an alternating current (AC) circuit, the direction of current flow reverses at a regular rate. Similarly, the voltage in a DC circuit remains constant, while it continuously varies in an AC circuit.
Batteries are capable of storing DC voltage only - they cannot store AC voltage. Most electronic circuitry runs on DC, and electronic appliances that run on AC power usually convert it to DC before it can be used. The advantage AC has over DC is that it can be transmitted over long distances with less loss than a DC circuit providing an equivalent amount of power.
AC circuitry produces a constantly varying magnetic field, and a constantly varying magnetic field will induce a current in an adjacent conductor. The induced current can be measured with a current meter. DC circuitry will only induce a current when a sudden change in the circuit takes place, such as powering it on. The induced current will "spike" briefly and then decay to zero.
Connect a buzzer, bell, or light with a battery using a switch in line.
Make and run a simple electric motor from a kit or take apart a motor and identify the parts, and explain how it works.
Make a simple battery cell.
A battery can be made placing a galvenized (zinc-plated) nail and a copper wire in a small container filled with vinegar. Do not let the zinc and copper terminals touch one another. They can be held apart by punching small holes in the container's lid and inserting them through these holes. A film canister works pretty well for this.
It might help to brighten the nail and the copper with sandpaper or emory cloth first. A cell constructed like this will generate about 0.8 volts. The copper wire will be the positive terminal (anode) and the zinc plated nail will be the negative terminal (cathode).
Connect multiple cells in series to form a battery and boost the voltage. When doing this, be sure to connect the positive terminal of one cell to the negative terminal of the other.
Connect multiple cells in parallel to boost the current capacity (necessary to light up a bulb). To do this, connect all the nails together with one wire and connect all the copper terminals together with another wire.
Demonstrate the ability to replace fuses or reset breakers and demonstrate a National Electric Code (NEC) approved splice using insulated wires.
There are many types of fuses. Some of them have threaded bases and can be removed by rotating them counter-clockwise. Others have to be pried out of their holders. Always remember that household current is dangerous, so it is best to cut the power first. This requirement can also be met by changing the fuse in an automobile or appliance (unplug first!).
A breaker is a current-sensing switch. Circuits can be turned off by flipping the switch away from the cetner of the breaker panel, and turned back on again by flipping the switch towards the center of the breaker panel. When a breaker senses that the current flowing through it exceeds its rated threshold, the switch opens by itself, moving the toggle between the off position and the on position. The breaker is said to have "tripped" when this happens. Before a tripped breaker can be reset, it must first be turned fully to the off position, and then it can be returned to the on position. If the breaker trips again, the circuit is still overloaded. If this is the case, turn off some of the appliances in the circuit before attempting to reset the breaker again.
