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Today: Electricity and Magnetism Basic Ideas Electrical Circuits ÆA circuit is always a circle. ÆA battery provides work to move charges (Q) around the circuit. The units here are volts (V) which equals the work per unit charge. To confuse college students, the common name for the physical quantity comes from the name of the units – voltage (V). To the right, we assume the battery provides V = 6 V. ÆThe black lines are wires. We assume the voltage never changes along a continuous wire. 6V V 0V ÆThe charge passing a given point per unit time is the current I. The units are amps (A). ÆThe jagged symbol represents a resistor. The voltage does change across a resistor. ÆFor convenience, lets define the green ground as the zero volts. 0V R Electrical Circuits – Ohm’s Law Ohm’s Law The voltage change across a resistor: V=IR 6V V 0V 0V R Electrical Circuits – Power Power ÆCharge Q gains potential energy QV while being pushed across the battery.The rate at which energy is gained is QV/t = (Q/t)V = IV. Remember, energy per time equals power. So, P=IV. ÆIn turn, the charge loses energy while crossing the resistor. The rate at which energy is lost is also P=IV. 6V R 0V ÆWe can also write the relationship as P = IV = I(IR) = I2R. ÆThe energy is changed to heat for a typical resistor. For a light bulb, it is heat + light. Heats up 0V Resistors in Series Resistors in Parallel Magnetism Magnetism