- Discuss the differences between series and parallel circuits - Introduce the concept of resistance - Conclude our hands-on study of electricity with construction of a complex circuit TODAY’S OUTCOMES: ELECTRICITY REMINDER: Complete the online attitude survey IMMEDIATELY if you have not already done so; it closes TODAY

GRADING OF PARALLEL CIRCUITS 5 points: 5 points:

1) In a series circuit, if one electrical device (bulb) is turned off, ALL the devices (bulbs) go off, because the circuit is broken - this would not be good in a house! 2) In a series circuit, the brightest of the bulbs depends on the number of bulbs, but in a parallel circuit the brightness stays the same.* * Brightness might change SLIGHTLY in a parallel circuit if there is a large change in the current drawn from the power source, but the change is generally small for a good battery or power source. 10. The circuit for the lights in a house resembles the circuit drawn at right. The bulbs are all in parallel. What are the advantages of wiring them this way, instead of putting them in series? 11. Terry claims there is another advantage: the additional light bulbs don’t cost anything to operate. He argues that the light bulbs are independent of each other, and so there is no way for the power company to know how many are turned on. Paula says there is a way for the power company to tell when a light bulb is turned on. Please explain who is right. Paula is correct - the power used is higher if more light bulbs are turned on. If more bulbs are lit, with the same brightness, then more current flows from the power source, and POWER increases with CURRENT. IMPORTANT: Current is the same at all points in a SERIES circuit; this is NOT true in a PARALLEL circuit.

CURRENT IN SERIES CIRCUITS 3 volts (assume all bulbs are identical) A B C D Currents through A, B, C, and D are all equal Currents through E, F, G, H and J are all equal Currents in the left diagram are GREATER THAN the currents in the right diagram 1) Current is the same at all points in a SERIES circuit. 2) Adding more devices/bulbs in SERIES reduces the current. 3 volts E F G H J Bulbs dimmer in right diagram

CURRENT IN PARALLEL CIRCUITS 3 volts (assume all bulbs are identical) A B C D Currents through A, B, C, and D are NOT all equal Currents through E, F, G, H and J are NOT all equal Bulbs are (almost) the same brightness in both diagrams 3 volts E F G J H The current splits at the green points ; so the current through A or D is the SUM of the currents through B and C Current A = Current D = Current B + Current C The current through E or J is the SUM of the currents through F, G, H Current E = Current J = Current F + Current G + Current H

CURRENT IN PARALLEL CIRCUITS 3 volts (assume all bulbs are identical) A B C D 3 volts E F G J Bulbs are (almost) the same brightness in both diagrams H 1) Current is NOT the same at all points in a PARALLEL circuit, and is highest in the wires leading to and from the power source 2) Adding more devices/bulbs in PARALLEL increases the current at the power source.

IS THERE A LIMIT TO HOW MANY DEVICES YOU CAN HOOK UP IN PARALLEL? No - but remember: The CURRENT near the power source keeps going up when you add more! CONSEQUENCES OF INCREASING THE CURRENT TOO HIGH: Power use goes up Too much power ⇒ HEAT In a house, this blows a fuse or trips circuit breaker

SIPHON ANALOGIES SERIES CIRCUIT – + = devices or bulbs PARALLEL CIRCUIT + = devices or bulbs – three outlets pull more water from the source than one Flow rate highest nearest to source, before the tube branches off

9. Susan made an extra bright flashlight. It has two batteries (like most flashlights) but three light bulbs. It gives off three times as much light, but the batteries don't last very long. Here is a diagram of Susan's flashlight. Explain how the concepts voltage, current, power, and energy are involved in this device; by the time you are done, you should have completely explained the sentence, " It gives off three times as much light, but the batteries don't last very long. " Adding extra bulbs in parallel to a common voltage increases the current drawn from the batteries, and thus the power used, which increases total brightness. A higher power flashlight increases the rate at which energy is used, depleting the batteries faster.

- How series and parallel circuits are different - What happens in a parallel circuit when more elements are added - Where the current is greatest in a parallel circuit and why WHAT YOU ARE EXPECTED TO KNOW:

Study materials between now and then: 1) Reading assignment on electrical safety at end of today’s lab (read by Monday) 2) Test practice problems and review sheet (to be handed out Monday) TEST ON ELECTRICITY: OPEN NOTE NEXT FRIDAY 9/16/11 TODAY IS THE LAST ELECTRICAL CIRCUIT LAB; MONDAY WE CONTINUE WITH NEXT UNIT

- Discuss the differences between series and parallel circuits ✓ - Introduce the concept of resistance - Conclude our hands-on study of electricity with construction of a complex circuit TODAY’S OUTCOMES: ELECTRICITY