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Electrical curcuits
- 1. ELECTRICAL CIRCUITS All youneed to be an inventor is a good imagination and a pile of junk. -Thomas Edison
- 2. Ohm’s Law I =V / R Georg Simon Ohm (1787-1854) I = Current (Amperes) (amps) V = Voltage (Volts) R = Resistance (ohms)
- 3. Howyoushouldbethinking aboutelectriccircuits: Voltage: a forcethat pushes the current through the circuit (in this picture it would be equivalent to gravity)
- 4. Resistance: friction that impedesflow of current through the circuit (rocks in the river) Howyoushouldbethinking aboutelectriccircuits:
- 5. Current: the actual “substance”that is flowing through the wires of the circuit (electrons!) Howyoushouldbethinking aboutelectriccircuits:
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- 9. The Central Concept:Closed Circuit
- 10. circuit diagram cell switchlampwires Scientists usually draw electric circuits using symbols;
- 11. Simple Circuits • Seriescircuit – All in a row – 1 path for electricity – 1 light goes out and the circuit is broken • Parallel circuit – Many paths for electricity – 1 light goes out and the others stay on
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- 13. PARALLEL CIRCUIT • Placetwo 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?
- 14. measuring current Electric currentis measured in amps (A) using an ammeter connected in series in the circuit. A
- 15. measuring current A A Thisis how we draw an ammeter in a circuit. SERIES CIRCUIT PARALLEL CIRCUIT
- 16. measuring voltage The ‘electricalpush’ which the cell gives to the current is called the voltage. It is measured in volts (V) on a voltmeter V
- 17. measuring voltage V This ishow we draw a voltmeter in a circuit. SERIES CIRCUIT PARALLEL CIRCUIT V
- 18. OHM’s LAW • Measurethe current and voltage across each circuit. • Use Ohm’s Law to compute resistance Series Circuit Voltage Current Resistance Voltage Current Resistance Parallel Circuit
- 19. measuring current SERIES CIRCUIT PARALLELCIRCUIT • current is the same at all points in the circuit. 2A 2A 2A • current is shared between the components 2A2A 1A 1A
- 20. fill in themissing ammeter readings. ? ? 4A 4A 4A 3A? ? 1A ? 3A 1A 1A
- 21. The circuit isno longer complete, therefore current can not flow The voltage decreases because the current is decreased and the resistance increases.
- 22. The current remainsthe same. The total resistance drops in a parallel circuit as more bulbs are added The current increases.
- 23. Series and ParallelCircuits • Series Circuits – only one end of each component is connected – e.g. Christmas tree lights • Parallel Circuits – both ends of a component are connected – e.g. household lighting
- 24. copy the followingcircuits and fill in the missing ammeter readings. ? ? 4A 4A 4A 3A? ? 1A ? 3A 1A 1A
- 25. Different cells producedifferent voltages. The bigger the voltage supplied by the cell, the bigger the current. measuring voltage Unlike an ammeter, a voltmeter is connected across the components Scientist usually use the term Potential Difference (pd) when they talk about voltage.
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- 27. series circuit 1.5V • voltageis shared between the components 1.5V 3V
- 28. • voltage isthe same in all parts of the circuit. 3V parallel circuit 3V 3V
- 29. measuring 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.
- 30. measuring current &voltage V V 6V 4A A A a)
- 31. measuring current &voltage V V 6V 4A A A A b)
- 32. answers 3V 3V 6V 4A 4A 6V 6V 6V 4A4A 2A 2A 4A a) b)
- 33. Voltage, Current, andPower • 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 = Watts • So the formula for electrical power is just: P = VI: power = voltage current