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Transcript
In Series and Parallel Circuits: Pearson Investigating Science 9 11.1 Potential Difference = Voltage “the pushing force” Voltage is a comparison between the pushing force of electrons between two points in a circuit. Symbol for voltage is V Measured in volts Units are V V=IR At each point in a circuit where the electrons need to be pushed, they use up their voltage. By the time the electricity gets back to the battery, the voltage is all used up and is 0 V. Series Circuits Voltage decreases as electrons cross each electrical load (and lose energy) Voltage across the source equals the sum of the voltages across each electrical load Vs = V1 + V2 + V3 Parallel Circuits If the loads are identical, the voltage is the same everywhere Vs = V1 = V2 = V3 Pearson Investigating Science 9 11.1 Current “the number of moving electrons” Current is the measure of the amount of charge moving past a point in a circuit every second. Symbol for current is I Measured in amperes Units are A I =V R In a series circuit the current is the same at every point in the circuit. Series Circuits Current is the same everywhere Is = I1 = I2 = I3 Parallel Circuits Current is not the same everywhere Current entering or leaving the source equals the sum of the current passing through each electrical load Is = I1 + I2 + I3 Each student (electron) starts at the ATM (source) to take out $3 (voltage – 3V). One store (load): the whole class (current) goes to 1 store and each student spends their $3. Everyone wants to spend all of their money because it’s a field trip! Current stays the same, voltage is the same as the source Two stores (loads): the whole class goes to each store, spending some of their money at each. Everyone wants to spend all of their money, but also wants to buy something at each store! Current is the same, voltage of loads will add up to V of source Everyone meets back at the ATM because they’re broke (V = 0) and have no more money to spend. This is the end of the field trip! Each student (electron) starts at the ATM (source) to take out $3 (voltage – 3V). One store (load): same as before! Current stays the same, voltage is the same as the source Two stores (loads): half of the class (current) goes to one store spending their $3, while the other half goes to the other store, spending their $3. Everyone wants to spend all of their money because it’s a field trip! Current of loads adds up to A at source, voltage is the same Everyone meets back at the ATM because they’re broke and have no more money to spend. This is the end of the field trip! Pearson Investigating Science 9 11.1 “how hard it is for electrons to flow” Resistance Resistance is the amount that a substance or load is opposing the flow of electrons FOUR FACTORS AFFECTING THE RESISTANCE OF A WIRE Symbol for resistance is R Measured in ohms Units are R =V I Material Gold is a better conductor than copper Length more wire = more resistance less wire = less resistance has less resistance than Cross-sectional Area A 50 metre extension cord has more resistance than a 10 metre extension cord. The thicker the wire, the less resistance it has. Temperature Electronics work better in the cold because wires have more resistance when they are hot. A resistor is any material that can slow current flow and through that converts electrical energy to other forms like heat, light, sound, and motion Series Circuits Equivalent (total) resistance equals the sum of the individual electrical loads RE = R1 + R2 + R3 Parallel Circuits Equivalent (total) resistance of the circuit is smaller than the smallest resistance Definition Units Symbol The rate at which electrons move from one place to another Ampere (A) I Voltage Measures the amount of (Potential energy given to electrons to Difference) move them Volt (V) V Resistance Degree to which a substance opposes the flow of electric current through it Ohms (Ω) R Current Pearson Investigating Science 9 11.1 A voltmeter measures the potential difference between two points in a circuit. Actually this is a multimeter. It can measure voltage, current and resistance. It depends on what you set the dial to and how you attach the meter. Voltmeter Turn the dial to “V” for volts Attach voltmeters in parallel. This means that you can attach it to the circuit without first having to cut the circuit. The black lead is “negative” and plugs into the common plug. The red lead is “positive” and plugs into the plug labeled “V”. Pearson Investigating Science 9 11.1 Ammeter A ammeter measures the current traveling at one point in a circuit. Actually this is a multimeter. It can measure voltage, current and resistance. It depends on what you set the dial to and how you attach the meter. Turn the dial to “A” for amperes Attach ammeters in series. This means that you have to cut the circuit and place the ammeter into the circuit. The red lead is “positive” and plugs into the plug labeled “A”. The black lead is “negative” and plugs into the common plug.