Series Circuit: Sequential Path (page 2)

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Author: Janice VanCleave

Try New Approaches

  1. Would it affect the lamp's brightness if the electricity flowed in a reverse direction through the lamp? Repeat the experiment, rotating the battery holder 180° so that the positive (red wire) and negative (black wire) terminals are reversed.
    1. Would adding more lamps in the series circuit affect the brightness of each lamp? Repeat the original experiment, using two lamps in sequence. Use a 4-inch (10-cm) piece of 22-gauge wire to connect the lamp holders. Use wire cutters to strip a small section from each end of the wire and attach the bare wires to one screw on each of the lamp holders. Science Fair Hint: Use a schematic drawing, such as the one in Figure 17.2, to show a two-lamp series circuit.


      Series Circuit: Sequential Path

    2. When lamps are connected in a series, what happens when one burns out? Determine this by unscrewing one of the lamps that is connected in series. (Note: When a lamp burns out, the filament in the lamp breaks. Thus unscrewing the lamp gives the same effect as using a burned-out lamp.)
  3. What effect does an increase in the number of batteries used have on the brightness of the bulbs? Repeat the original experiment, using one bulb and connecting two 1.5-V batteries in series by using a wire to join the negative terminal of one battery to the positive terminal of the other. 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.

Design Your Own Experiment

    1. Coulomb (C) (charge on 6.25 × 1818 electrons) is the SI unit for quantity of electric charge. One coulomb per second is called an ampere (A) (unit measure of electric current), more commonly called amps. A device used to measure the amount of electric current in a circuit is called an ammeter. A multitester is an instrument that has the ability to work like a number of instruments, including an ammeter and a voltmeter (an instrument used to measure voltage). A multitester can be purchased at an electronics store. Design an experiment that uses a multitester as an ammeter to measure the current in any or all of the series circuits in the previous experiments. Follow the directions provided with your multitester, but note the information shown here for the multitester used by the author. Caution: An ammeter is always connected in series. This means that when using the multitester to measure current, you must break the circuit being measured and make the ammeter part of the circuit. You can ruin the multitester if this is not done. Figure 17.3 shows a diagram of a circuit with a battery, lamp, switch (device used to open and close an electric circuit), and ammeter. The author's multitester has a scale for measuring DC current from 0 to 150 rnA (milliamps). To measure current, the function selector is set to 150 rnA DC (see Figure 17.4). Attach the negative test lead (black) from the multitester to the negative side of the circuit and the positive test lead (red) to the positive side of the circuit, as shown in Figure 17.4. Only the DCV /rnApart of the scale on a multitester is shown in Figure 17.4. While numbers are not printed on this scale, with the tester selector set to 150 rnA DC, the fifteen long marks on the scale each measure 10 rnA, which is read as 10 milliamps. The current reading for the circuit in Figure 17.4 shows the scale needle on the small mark between 30 rnA and 40 rnA; thus the current is 35 rnA and is equal to 0.035A.
    2. Series Circuit: Sequential Path

    3. Does it matter where in the circuit the multitester is placed? Design series circuits and use the multitester to test in different places along the circuit, such as between two lamps or on the positive side of the battery and then on the negative side.
    4. Series Circuit: Sequential Path

  2. The driving force that pushes the electrons around the circuits in the experiments in this chapter is the battery, which acts like an electron pump. Voltage is a measure of the amount of potential energy that the battery transfers to electrons in a circuit. It is a measure of the difference in the energy on either side of the cell. The unit measure of voltage is volts (V). A multitester can act as a voltmeter. Design an experiment so that voltage can be measured. You may wish to place a switch in the circuit to make it easier to open and close the circuit. Use the multitester to measure the voltage in any or all of the series circuits in the previous experiments. Follow the directions provided with your multitester, but note the information shown here for the multitester used by the author. Caution: A voltmeter should NEVER be part of a circuit; instead, it should be connected across a circuit. Set the function selector to the lowest DC V position, which is 15 on the author's multitester. To determine the voltage through one of the lamps, touch the negative test lead (black) to the negative side of the circuit and the positive test lead (red) to the positive side of the circuit, as shown in Figure 17.5A The voltage in the diagram is read as 1.5 volts. Figure 17.5B shows a schematic for the circuit with a voltmeter.
  3. Each device in a circuit affects the flow of electrons, and some restrict the flow more than others. Any device in a circuit, such as a lamp and wire, offers resistance. But a device that is used to create electrical resistance in an electric circuit is called a resistor. Resistance is measured in the SI unit of ohm (Ω). A multitester can be used to measure resistance, but the resistance of the circuits in this chapter may be too low to be measured accurately by the tester. Instead, since the voltage and the current can be measured, the relationships among voltage, current, and resistance, known as Ohm's law, can be used to calculate resistance. This relationship is expressed as V = I x R, which is read: V voltage (in volts) equals I, current (in amperes) times R, resistance (in ohms). If the voltage and the current are known, the resistance can be calculated using the following formula:
      R=V ÷ I
  4. For example, if a circuit has a voltage of 1.5 V and a 35 rnA current, the resistance would be:

      R = 1.5 V ÷ 0.035 A = 42.85 Ω

    For more information about Ohm's law, see Karl F. Kuhn, Basic Physics: A Self-Teaching Guide (New York: Wiley, 1996), pp. 152–153.

    Series Circuit: Sequential Path

Get the Facts

A battery is made of one or more electrical cells connected in series. What are electrical cells made of? Is a flashlight battery technically a battery or a cell? How do electrical cells produce the driving force of the battery? What is a dry cell? What is the electric potential of a battery. and what causes it? For information. see physics texts as well as Mary and GeoffJones. Physics (New York: Cambridge University Press, 1977), pp. 202–203.

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