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LAB_3 - Parallel and Series

LAB_3 - Parallel and Series - Lab 3 Parallel Series...

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Lab 3 43 Parallel & Series Circuits Summary The design and use of electric measuring circuits requires an understanding of the relationships that exist when circuit elements are connected in various configurations. Series connections allow only one path for the current while parallel connections allow multiple paths for current but share a common applied volt- age. Most circuits are combinations of these two types of connections and hence are called series-parallel combination circuits. In this experiment you will create and study the characteristics of some of these combinations. After performing this experiment the student should be able to: 1. Build series, parallel and combination circuits. 2. Use voltage division to provide different voltages in a series circuit. 3. Calculate the equivalent resistance of a series-parallel combination circuit. 4. Verify Kirchoff ’s Voltage and Current Laws experimentally. 5. Demonstrate the use of a Wheatstone Bridge. Background Information Current flow in the series or tandem circuit is illustrated in figure 1. In a series circuit, if we assume conservation of charge, the same current must flow through all the circuit elements. The above figure illustrates current flow with the positive charge convention although we now know that current is due to the flow of free electrons. Although the current is the same for each element in a series circuit, the voltage is "shared unequally". The less resistive elements get a smaller share and the more resistive elements get a larger share. The potential difference V i across each element in the circuit can be found using Ohm’s Law: "You cannot teach a man anything; you can only help him to find it within himself." - Galileo Galilei

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Lab 3 44 Since the current I is the same through each element, the potential differences must be unequal if the resistors are unequal. We shall choose node 0 in Figure 1 as the ground reference. At node 1, the potential difference is the voltage V provided by the power source. At node 2 the voltage has been reduced by V 1 due to the current passing through resistance R 1 . So at node 2 the potential difference with respect to ground is V V 1 . Likewise at node 3 the potential difference is V V 1 V 2 . Continuing around the circuit and back to node 0, the potential difference is V V 1 V 2 V 3 . Since we are now back at the ground reference point, we conclude that: This result is a special case of: (1) Figure 1: Current flow ivn a series circuit. (2) Kirchoff's Voltage Law: Around any closed loop, the algebraic sum of the voltages equals zero. V IR i i = V V V V = 1 2 3 0
Lab 3 45 Open and Shorted Circuits A complete circuit has no gaps or breaks to prevent current from flowing through it. Conversely, an incomplete circuit has some path break or gap through which the current cannot flow. A circuit with such a break is called an open circuit and is illustrated in Figure 2.

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LAB_3 - Parallel and Series - Lab 3 Parallel Series...

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