Where ξ is the voltage of the source, e is the base of the ________, R is the resistance of the resistor in the RC circuit, and C is the capacitance • The charge within a capacitor is given by Q= Q0 (1 − e−tRC) • Time COnstant- The product of resistance and capacitance in an RC circuit, represented by τ τ= RC • The voltage across a resistor in an RC circuit is calculated by VR= ξe −t /RC Thus current is ξe−t /RC I= R Capacitor Discharging • The voltage in a capacitor as it discharges is VC= V0e−t /RC • The charge as it discharges is Q= Q0e−t /RC Medical and Other Applications of RC Circuits • Sawtooth Voltage- A voltage whose graph resembles a saw blade • Electronic Pacemaker- A medical device that uses an RC circuit to deliver evenly spaced electrical pulses to the heart 19.7 Electric Hazards • Electric current running through the body may cause burns or stimulate nerves annd muscles • Ventricular Fibrillation- Occurs when a high current passes trhough the heart, it will cause irregular rhythms and blood is not properly pumped Safe Wiring • Power outlets contain 3 wires, the hot wire from which current flows, the neutral wire which carries away current, and the ground wire that connects to ground • Circuit Breakers- Devices that dtecte when too much current flows thruogh a wire, if the current passes over the threshold then it stops current from flowing • Leakage Current- Current that flows along an unintended path 19.8 Ammeters and Voltmeters- Measurement Affects the Quantity being Measured • Ammeter- A device that measures current • Voltmeter- A device that measures voltage • Galvanometer- An analog ammeter or voltmeter that works by using the force between a magnetic field and a current carrying coil How to Connect Meters • Ammeters must be connect directly within a circuit • Voltmeters are connect in parallel with the points between which voltage is being measured Effects of Meter Resistance • Sometimes, a meter can give a misleading reading • Voltmeters with high resistances compared to the circuit they are measuring have more accurate readings • The more sensitive a galvanometer is, the less its effect on the circuit is Other Meters • Multimeter- A meter that measure multiple electrical units • Ohmeter- A meter that measures resistance Digital Meters • Digital meters do not use a galvanometer but rather use semiconductor devices to measure • Their precision is extremely high, often around 0.01 %.
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