Experiment 2-5. Wheatstone Bridge experiment Use the Wheatstone Bridge to measure the unknown electrical resistance and learn the structure and principles of the Wheatstone Bridge. In the laboratory, the following devices are prepared for this experiment. 1 Ready-Set Wheatstone Bridge Experimental equipment A. DC power supply 5V B. Variable resistor 100Ω, 1kΩ, 10kΩ, 50kΩ, 100kΩ (5Steps) C. 1-3. Hundreds of Ω~Dozens of kω (12Steps) D. 1-4. Digital galvanometer 1μA E. 1-5. Stick-slip resistance wire 20cm F. 1-6. Vernier calipers for measurement 2 Multimeter 1EA 1) Connect the Wheatstone Bridge with fixed voltage 5V. 2) Rotate the A dial to set the unknown resistance 1 and turn on the galvanometer.
Fig.1 All-in-one Wheatstone Bridge Experimental equipment 3) Place the solenoid type stick-slip resistance wire terminal at the center position. Turn the dial to select so that no alarm sounds. If there is no such value, is selected as near as possible to the center. * The experimental system is designed to give a warning sound when a current exceeding a certain level is applied to the galvanometer, and it is advantageous that the experiment is performed near the center rather than at both extremes of the variable resistance. It is recommended that the experimental values at both extreme ends be measured by measuring the voltage according to the length of the variable resistor and correcting it through the relationship graph. 4) Adjust the position of the stick-slip resistance wire terminal so that the zero point of the galvanometer is adjusted to 0, and read the value through the attached Vernier calipers. 5) Calculate and record the unknown resistance from equation (5). 6) Rotate the dial to change the number of unknown resistances in the sequence of 2 to 12, and repeat steps 3) to 5). 7) Measure the unknown resistance directly with a multimeter and record the measured value. (Caution: 1. Even in the case of a ready-set experiment, it is the most basic step in the experiment to verify that the actual resistance is the same value as the indicated resistance. Let's see if the value shown is the same as the actual resistance. (Where the resistances are 1k, 5k, 10k, 15k, 20k from the top. Also, when checking these resistors, you should check the resistors to be checked without connecting them to the circuit) 2. The coil is wound on the bottom of the circuit. Basically, if the number of turns per unit
length is the same and the types of resistors are the same, the resistance will be divided by half in the middle. Is it really like that? Let's look for a location where the resistance is exactly half through a voltmeter.) 8) The results obtained from experiments and theories are compared with the results directly measured by the multimeter and the relative errors are obtained. It is recommended to write experiment notes in the following way. 1. Measurements and calculations Variable resistor Unknown resistor Measures Relative error (%) No. Variable resistor NO. (kω) Unknown resistor NO. Multimeter Measures(kΩ) (cm) (kω) 1 2 3 4 5 6 7 8
9 10 11 12 2. Error analysis 3. Conclusion and Discussion The Wheatstone bridge is a device that connects the resistances as shown in Figure 2, connects the galvanometer G between point B and point D, and finds the potential difference between the two points. is the unknown resistance that we want to measure, and is the known value of the known resistance. In the circuit shown in Fig.2, when the values of the resistors and are appropriately selected, the currents do not flow due to the equipotential between the point B and the point D. Since there is no current between BD, the same current flows in and, and the same current flows in and. From this, the potential difference across each resistor is (1) -
3 (2) and, from,, Fig..2 Wheatstone bridge is established. From equation (2), we can derive 4 (3) Therefore, the unknown resistance can be obtained by knowing the value of and the ratio of the two resistances.
Fig.3 Ready-Set Wheatstone bridge In the Ready-Set Wheatstone bridge as shown in Fig. 3, and are solenoid-type stick-slip resistance wire with a diameter, and the wire is a uniform resistance line with a resistivity and diameter of. If the length of the resistor is, and the length of the resistance is Each resistance value is, So, The ratio of two resistances is (4) and Substituting equation (4) into equation (3), Unknown resistance is So, the two lengths and of the sliding resistance line can be measured and the unknown resistance can be obtained from the known resistance. (5) 1) 김경헌외 15 인, 대학물리학, ( 청문각, 2007), 제 18 장.
2) D. Halliday et al, FUNDAMENTALS OF PHYSICS, (John Wiley & Sons, Inc. 2005. 7/E), Chapter 31. 3) 한국물리학회, 일반물리학실험, ( 請文閣, 1997), p.357