Objectives: The student should be able to:

 1 diagram and construct series and parallel circuits.

 2 describe the effects of series and parallel connections on actual circuits.

Materials: circuit boards, flashlight cells, battery holder, connecting wires

Background: A series circuit is one in which electricity flows along a single conductor through two or more loads.  In a parallel circuit, the electricity has more than one path through the circuit.  A typical two-cell flashlight has the cells connected in series.  The voltage of the battery formed in this way is determined by adding the voltages of the cells.  When similar cells are connected in parallel, the battery formed has the same voltage as a single cell.  This type of battery will last longer than a single cell.  The circuits in a house are connected in parallel.

Cells in Series.  Connect one cell to one bulb.  If you have a complete circuit, the bulb should light.  Describethe result.  Predictthe results of connecting two cells in series.  Now connect two cells in series to one bulb.  Record your observations. In a similar fashion, firstpredict resultsand then connect three and then four cells in series andrecord the results.

        a) What effect did adding cells have on the brightness of the bulb?  

        b) Why is that?  

        c) What do you estimate the voltage to be in each trial?  

        d) What effect does increasing voltage have on the brightness of the bulb?

Cells in series

        Bulbs in Series.  Using the four cells connected in series to form a six-volt battery, connect one bulb in series with the battery.Record your observation.  Now connect a second bulb in series with the first.Comparethe brightness of each bulb with the brightness of the single bulb.  Predictthe results of adding a third bulb.  Connect the third bulb in series with the other two anddescribe the results.  Disconnect any wire in the bulb circuit.  Observe andrecord the results.

        e) What are the disadvantages of connecting light bulbs in series?  

        f) Are there any advantages to connecting light bulbs in series?

Bulbs in series

        Bulbs in Parallel.  Disconnect all wires.  With the cells connected to form a six-volt battery, again connect one bulb in series with the battery.  Make noteof the brightness of the single bulb.  Connect a second bulb in parallel with the first and observe andrecordthe results.  Predictthe results of adding a third bulb.  Now connect a third bulb in parallel and observe andrecord.  Without disconnecting the whole circuit, unhook one bulb.  Describe the results.

        g) Did the other two bulbs stay lit when one was disconnected?

        h) Did the bulbs dim or brighten?  Reverse the wire from the battery to the circuit.

        i) Does this have any effect on the bulbs?  Explain what you observe.

Bulbs in parallel

        Further Investigation.  Connect one bulb in series with two bulbs that are connected in parallel.  Connect this with the six-volt battery.  

        j) Describe and explain what you observe using a water flow analogy.  

More Questions.  

        k) What is the advantage to connecting flashlight cells in series? in parallel?

        l) Why are electrical circuits in homes connected in parallel?

        m) What would be the effect of adding a fourth bulb to the series circuit?  to the parallel circuit?