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# Parallel Circuit (page 2)

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Author: Janice VanCleave

1. Do the lamps in a parallel circuit have to be geometrically parallel to each other, or just connected so that the electrons have different paths from the negative side to the positive side of the battery? Design different electrical schematics, such as the one shown in Figure 49.4 Then assemble the circuits using the indicated lamps and battery for each schematic. Allow the brightness of the bulbs to indicate any change in the flow of the current through them.
2.
1. Ohm's law describes the total current in a parallel circuit (It) as the sum of the currents in each branch of the circuit. Design a circuit with two or more lamps in parallel to confirm that for devices in parallel It = I1 + I2 + IN. In the equation, It is the total current, I1 is the current through lamp 1, I2 is the current through lamp 2, and IN represents the sum of other lamps in parallel, such as I3, I4, and so on. Use a multitester, such as the one described in Chapter 48, to measure the currents.
2. Ohm's law describes the voltage of lamps in parallel as the same as the total voltage of the circuit. Use the circuit in the previous experiment and the multitester to confirm that Vt (total voltage) + VN (sum of voltage across other lamps in parallel) = V1 (voltage across lamp 1) + V2 (voltage across lamp 2). For more information about parallel circuits, see Karl F. Kuhn, Basic Physics: Self-Teaching Guide (New York: Wiley, 1996), pp. 152–158.
3. Battery cells in series are connected so that the anode (positive terminal) of one cell is connected to the cathode (negative terminal) of another cell. In parallel cells, like terminals are connected, anode to anode and cathode to cathode. Figure 18.5 shows two batteries connected in series and two batteries connected in parallel. Design an experiment to determine the effect of parallel cells on the current and voltage of a circuit. One way is to connect two batteries in parallel, then assemble a circuit with this parallel battery, a lamp, and a switch. CAUTION: Use only 1.5-V batteries. Connecting more than two 1.5-volt batteries in a series or using batteries with a greater voltage may burn out the lamp as well as produce a dangerous amount of current. For more information about batteries, see Mary and Geoff Jones, Physics (New York: Cambridge University Press, 1997), pp. 202–203.

### Get the Facts

Christmas lights were at one time wired in series to save on cost, but most are now wired in parallel. What effect did a burned-out bulb have when the bulbs were in series? In parallel? Which is used in homes—series or parallel circuits? For information, see P. Erik Gundersen, The Handy Physics Answer Book (Detroit: Visible Ink, 1999), pp. 313–314.

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