INVESTIGATION 2: CURRENT AND VOLTAGE IN PARALLEL CIRCUITS There are two basic ways to connect resistors, bulbs or other elements in a circuit-series and parallel. So far you have been connecting bulbs in series. To make predictions involving more complicated circuits we need to have a more precise definition of series and parallel. These are summarized in the box below. Series comection: Share one junction Two zesistors or bulbs are in series if they are comected so that the same current that passes through one zesistor or bulb passes through the other. Thatis, there is only one path available for the current. Series Pazallel comection: Share two junctions Two zesistors oz bulbs are in parallel if their terminals are commected together such that at each jinction one end of a zesistor or bulb is dizectly comnected to one end of the other resistor or bulb, e.g. junction 1 in the diagiam. Similarly, the other ends are commected together (junction 2). i junction 1 junction 2 Parallel Let's compare the behavior of a circuit with two bulbs wired in parallel to the circuit with a single bulb. (See Figure 2-5 below.) E () (b) Figure 2-5: Two different circuits with identical components-(a) a single bulb circuit and (b) a circuit with two identical bulbs connected in parallel to each other and in parallel to the battery. Note that if bulbs A, D and E are identical, then the circuit in Figure 2- 6 is equivalent to circuit 2-5(a) when the switch is open (as shown) and equivalent to circuit 2-5(b) when the switch is closed. Real Time Physics: Active Learning Laboratory E Figure 2-6: When the switch is open, bulb D is connected in parallel to the battery. When the switch is closed, bulbs D and E are connected in parallel to each other and in parallel to the battery. Question 2-1: Explain how to determine from the configuration of the circuit that D&E are in parallel when the switch is closed. Prediction 2-1: With the switch closed, predict how the brightness of bulbs D and E in the parallel circuit of Figure 2-5 (b) will compare to bulb A in the single bulb circuit of Figure 2-5 (a). How will D and E compare with each other? Rank the brightness of all three bulbs. Explain the reasons for your predictions. Activity 2-1: Brightness of Bulbs in a Parallel Circuit Set up the circuit in Figure 2-6, and describe your observed rankings for the brightness of bulb D with the switch open, and D and E with the switch closed. Question 2-2: Did the observed rankings agree with your prediction? If not, can you explain what assumptions you were making that seem false? Prediction 2-2: Based on your observations of brightness, what do you predict about the relative amount of current through each bulb in a parallel connection, i.e., bulbs D and E in Figure 2-5 (b)? Prediction 2-3: Based on your observations of brightness, how do you think that closing the switch in Figure 2-6 affects the current through bulb D?