# yr9 - ohms law and circuit types

Post on 07-Aug-2015

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1. 1. Dr Pusey www.puseyscience.com Q: Write a definition for Current, Voltage and Resistance
2. 2. Ohms Law Ohms law says that the Current running through a circuit is controlled by the Voltage and the Resistance. = = = I R V
3. 3. Ohms Law Quiz I R V Voltage Current Resistance 0.5 A 4 6 V 4 8 V 2.0 A 10 V 4 12 V 3.0 A V A Find the unknown values Show your working out!
4. 4. Ohms Law Quiz I R V Voltage Current Resistance 4x0.5 = 2 V 0.5 A 4 6 V 6/4 = 1.5 A 4 8 V 2.0 A 8/2 = 4 10 V 10/4 = 2.5 A 4 12 V 3.0 A 12/3 = 4 V A Find the unknown values The resistance of the resistor stayed the same! This means that it is Ohmic
5. 5. Ohmic or Non-Ohmic All circuit components (even the wires) have a resistance. Ohmic (a): Resistance is the same, no matter what voltage is applied. Examples: Most Resistors, Wire Non-Ohmic (b): Resistance changes with voltage Examples: Lights, Computers
6. 6. Series circuits Current must flow through devices sequentially Current only has one path to follow Current is same at any point in the circuit Total Voltage is split/shared across components Extra components in series increases the resistance, which _________ the current. If something breaks in a series circuit, the whole thing stops working. Q: EXPLAIN WHY^^
7. 7. Parallel circuit At least two different pathways for current to travel Current is shared between different pathways. Total voltage across components is the same Extra components draw more current. E.g. New Christmas lights
8. 8. Series and Parallel Series Circuits Parallel Extra components reduce the current Extra components increase the current One broken component stops circuit One broken component has no effect Requires less wiring Requires more wiring A switch controls everything Multiple control points Draws less power Draws more power Components affect each other (adding more will affect how they perform) Components are independent from each other.
9. 9. Quick Quiz Draw circuits showing three lights controlled by one switch (like Christmas lights). A) Draw the lights in series B) Draw the lights in parallel C) Would the lights be brighter in A, or B? Or are they the same brightness? Justify your reason D) For each case, discuss what would happen to the brightness if you added another lamp.
10. 10. Quick Quiz A) Draw the lights in series B) Draw the lights in parallel C) Would the lights be brighter in A, or B? Or are they the same brightness? Justify your reason B, because each globe has a direct connection to the battery, so more current can circulate than in A D) For each case, discuss what would happen to the brightness if you added another lamp. In (A), they would go dimmer due to additional resistance In (B), they wouldnt change, because they are independent of each other
11. 11. Short Circuits How? When the normal pathway is cut short due to a conductor incorrectly connecting two points. Note: Humans make excellent conductors DANGER! If a human is causing a short circuit, they will conduct the current, which causes an electric shock. Other problems with short circuits: Sensitive components receive too much current and stop working Overheating of batteries KABOOOOOOM!
12. 12. Safety Fuses - Safety for the circuit and humans Fuses are simply a special wire, connected in series If the wire receives more current than its supposed to, it will melt away and there will be no pathway for electricity to flow: