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Equivalent resistance of parallel branches. There is another way of determining total resistance in a parallel circuit (but only for certain cases). If the resistance in each branch is equal, then the total or equivalent resistance of the branches is equal to the resistance of one branch divided by the number of branches. With a parallel circuit: Voltage remains the same for each branch. Current will vary, based on the resistance within that branch. To find the current for a single branch, you will need to divide total Voltage by the Resistance for that branch. This is more complicated if you have more than one resistor in a particular branch. You can check your work with this method. The amount of current for all individual branches should add up to the Itotal for the circuit. For a circuit with Itotal = 3.6 Amps, you may end up with a total of 3.56 Amps when adding the branches separately. Complex Circuits: Complex circuits involve a combination of both parallel and series circuits combined. These are the most common circuits you will find in a house, because they allow appliances to have independent switches (parallel circuit), while a circuit breaker can be wired in series to the parallel paths, protecting the appliances from any power surge. Electrical Safety Components Fuses are short pieces of metal designed to melt when too large a current passes through. The thickness of the metal determines the amount of current that the fuse can tolerate. Surge Protectors and Ground Fault Interrupters are designed to prevent excessive amounts of electrical energy from damaging people and/or electronic devices. Surge protectors are used to detect voltage spikes and then shut down the circuit to prevent damage to the electronics. Ground Fault Interrupters are designed to protect from electrical shock by interrupting a household circuit when there is a difference in the currents between the ground wire and the "hot" wire. A circuit breaker is an automatic switch that opens when a circuit encounters a certain level of current. The metal bends with the heat, causing the breaker to open. The circuit no longer receives current. In order to re-set the breaker, the metal switch must bend back into place (this happens when the temperature falls back to a normal level). Alternating Current (AC) and Direct (DC) Current DC Direct current refers to a circuit in which electrons are flowing in only one direction (batteries). When current begins to flow in a DC circuit, the magnetic field builds up. During that time, the field can induce current flow. Once that current is flowing, the induction stops. DC was the original circuit used by power plants, but they could only send electricity short distances before losing power. AC An alternating current source produces currents that flow in one direction and then the other, continuously cycling from positive to negative, and back. Each time current direction reverses, the direction of the magnetic field reverses. Since current alternates continuously, the magnetic field is never static. Power plants switched to AC circuits because they could carry electricity hundreds of miles with little loss of power. In addition, AC circuits (unlike DC) can be "stepped-up" or "stepped-down" using transformers. Transformers Transformers are used to increase or decrease AC voltage. Transformers consist of a "soft" metal core (usually iron) and two sets of coiled wire. The wire coils are arranged side-by-side, enabling the changing magnetic field of one to overlap the field of the other. The number of coils in the wire determines the amount of voltage on that side. In the example below, the primary (input) voltage is less than the secondary (output) voltage, so this would be a "step-up" transformer. A "step-down" transformer would have more coils on the primary side than the secondary. Transformers come in handy in transmitting electricity over long distances. Since AC travels more efficiently at high voltages, transformers are used to step up the voltage before the electricity is sent out, and then other transformers are used to step down the voltage for use in homes and businesses.