Lab 1 - Resistance

# Series the ends of the dmm labeled 1 and 2 are

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Series - The ends of the DMM (labeled 1 and 2) are connected by only one path; that is through the DMM itself. Therefore all current passing through the light bulb must also pass through the DMM (left-hand diagram of Figure ?? ). Parallel - Ends 1 and 2 are connected by more than one path. In the right-hand diagram of Figure ?? from point 1 to 2 current can flow both through the DMM as well as the lightbulb. Since both bulb and DMM are connected at the same points in the circuit the voltage across both will be the same. Now to test the behavior of the DMM as an ammeter and voltmeter, you’ll use both series and parallel configurations and verify which is correct. Figure 5: At left: ammeter connected in series with light bulb. At right: voltmeter connected in parallel with light bulb. On the Electronics Lab Board place a D-cell battery in one of the battery holders. Connect this battery to one of the light bulbs also mounted to the board. Make sure it lights and note its brightness. Configure the DMM to measure current and connect it in series with the light bulb. How much current is being read by the multimeter? Note the brightness of the bulb. Does it appear to be different from before? 6

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Has the DMM had a noticeable effect on the amount of current flowing through the bulb? With the DMM still in series reconfigure it to measure voltage. Does the bulb still appear to be the same brightness? What’s the voltage being read by the DMM? Does this value make sense considering how it’s attached to the circuit? Has the DMM had a noticable effect on the amount current flowing through the bulb? Next connect the DMM in parallel with the light bulb, leaving it configured to measure voltage. Again note the brightness of the bulb, how does it compare to that of the original circuit? What is the voltage difference being read by the DMM? How does it compare to the voltage supplied by the battery? Considering the bulb’s brightness how much current is flowing through it relative to the DMM (qualitatively)? With the DMM still in parallel, reconfigure it to measure current. Does the bulb still appear to be the same brightness? What current is being read by the DMM? How does this differ from when it was connected in series? What effect has the DMM had on the amount of current flowing through the bulb? Why? To best understand the difference between measuring current and voltage it helps to consider the multimeter as just another resistive element, much like the bulb. How is total resistance affected when a resistor of large resistance is connected in parallel? What if it’s resistance is very small? Similarly, how does total resistance change when a small and large resistor are subsequently placed in series with the existing circuit?
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• Spring '11
• shpyrko
• Resistance, Resistor, power amplifier, Current Probe

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