& volage is approximately Adjust the power source dial until its terminal 3. Dep
ID: 2041269 • Letter: #
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& volage is approximately Adjust the power source dial until its terminal 3. Depress one end of the sliding conlact so that it makes good contact with the slide 2. Ceenect wire. (This point is called poiet of Ri until the galvanometer balanced. If the galvanometer deflec B) Either end of the sliding contact-but not both- can be depressed. Vary the valoe reading is approximately zero the Wheatstone beidge is now tion tends to ecome larger as R. is varied, the value ofRi ?s too large and should be beidge is ap- 4. Reduce the galvanometer protective resistor to 400 . Move the sliding contact to the 4. Reduce t sain approximaleisoctive resistor from right or the left until the resistor from 400 ? to on in steps of 100 ?. For each value ofthe peotective 5. Reduce the galvanometer resistor, balance the bridge as in step 3, 6. When the bridge has been balanced with the protective resistor equal to 02, record the value of Ryon your data Record the lenghs Ly and I sheet. 7. Determine the lengths and L. in centimeters and omven dese values to meters. your data sheet. & Use equation 42.8 to compute the experimental value of R 9. Refer to Experiment 39 to obtain the theoretical value of R. Record this value on your data sheet. Record this value on your data sheet. Cakculate the percentage error in the experimental value of R sure to reset R, to 4.0 2, 10. Repeat steps I through 9 for each of the other resistances on the resistance board. Be protective resistor in series with the galvanometer to 500 0, and the tenminal voltage to 1.0 Vhe QUESTIONS is the Wheatstone bridge method more accurate for measuring resistance than the voltmeter-ammeter used in Experiment 39 2. What factors limit the accuracy of the Wheatstone bridge? e of the power source critical to the accuracy of your experimental results? Explain your 3. Is the terminal voltage answer 4. Can the resistors in an "unbalanced" Wheatstone bridge circuit be treated as a combination of series and/or perliled resistors? What about a "balanced" bridge? 5. What is he purpose of the resistor conected in series with the galvanometer? What would happen if'it were i tially set to on rather than to 500 324 Experiment 42 The Wheatstone BridgeExplanation / Answer
1) For the most accurate measurement of resistance, the Wheatstone Bridge circuit is used. This circuit avoids most of the difficulties of the ammeter-voltmeter method. This is a null method, in which no meter reading needs be taken except for a judgment of when the deflection of a galvanometer has been reduced to zero.
2) Some factors are resistance in the wires and null in connections. Temperature variance in resistance which we can control using specific material but cannot eliminate it.
3) With the exception of inaccuracies caused by excessive supply voltages, the accuracy of the Wheatstone bridge is, otherwise, independent of the value of supply voltages. The result is that an increase in the supply voltage increases the power dissipation (heat) of the bridge resistors.
4) Not sure about this one.
4) Because the galvanometer works on low current flow and has a low resistance.
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