10circuit diagramScientists usually draw electric circuits using symbols;celllampswitchwires
11Simple Circuits Series circuit Parallel circuit All in a row 1 path for electricity1 light goes out and the circuit is brokenParallel circuitMany paths for electricity1 light goes out and the others stay on
12123The current decreases because the resistance increases. Ohm’s Lawsays that I=V/R. The voltage in the system is constant, resistance increases.
13PARALLEL CIRCUITPlace two bulbs in parallel. What do you notice about the brightness of the bulbs?Add a third light bulb in the circuit. What do you notice about the brightness of the bulbs?Remove the middle bulb from the circuit. What happened?
14measuring currentElectric current is measured in amps (A) using an ammeter connected in series in the circuit.A
15measuring current A A This is how we draw an ammeter in a circuit. PARALLEL CIRCUITSERIES CIRCUIT
16measuring voltageThe ‘electrical push’ which the cell gives to the current is called the voltage. It is measured in volts (V) on a voltmeterV
17measuring voltage V V This is how we draw a voltmeter in a circuit. SERIES CIRCUITPARALLEL CIRCUIT
18OHM’s LAW Voltage Current Resistance Parallel Circuit Voltage Current Measure the current and voltage across each circuit.Use Ohm’s Law to compute resistanceSeries CircuitVoltageCurrentResistanceParallel CircuitVoltageCurrentResistance
19measuring current SERIES CIRCUIT current is the same at all points in thecircuit.2A2APARALLEL CIRCUIT2A2Acurrent is sharedbetween thecomponents1A1A
20fill in the missing ammeter readings. ?3A3A4A?1A??4A4A1A?1A
21The voltage decreases because the current is decreased The circuit is no longer complete, therefore current can not flowThe voltage decreases because the current is decreasedand the resistance increases.
22The current remains the same The current remains the same. The total resistance drops in a parallel circuit as more bulbs are addedThe current increases.
23Series and Parallel Circuits Series Circuitsonly one end of each component is connectede.g. Christmas tree lightsParallel Circuitsboth ends of a component are connectede.g. household lighting
24Circuit in Diagram Form +batterybulb_currentIn a closed circuit, currentflows around the loopelectrons flow opposite theindicated current direction!(repelled by negative terminal)Current flowing through thefilament makes it glow.No Loop No Current No Light
25copy the following circuits and fill in the missing ammeter readings. ?3A3A4A?1A??4A4A1A?1A
26measuring voltageDifferent cells produce different voltages. The bigger the voltage supplied by the cell, the bigger the current.Unlike an ammeter, a voltmeter is connected across the componentsScientist usually use the term Potential Difference (pd) when they talk about voltage.
28series circuitvoltage is shared between the components3V1.5V1.5V
29parallel circuit voltage is the same in all parts of the circuit. 3V
30measuring current & voltage copy the following circuits on the next two slides.complete the missing current and voltage readings.remember the rules for current and voltage in series and parallel circuits.
34Voltage, Current, and Power One Volt is a Joule per Coulomb (J/C)One Amp of current is one Coulomb per second (6.24 x10^18 electrons/second).If I have one volt (J/C) and one amp (C/s), then multiplying gives Joules per second (J/s)this is power: J/s = WattsSo the formula for electrical power is just:More work is done per unit time the higher the voltage and/or the higher the currentP = VI: power = voltage current