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R a. I a. I C. R C. I D. I b. R b. R D. A. Lab 5: Wheatstone Bridge Only 7 more labs to go!!. The Wheatstone Bridge is a commonly used circuit for making electrical measurements. When will the current through the ammeter be equal to zero?
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Ra Ia IC RC ID Ib Rb RD A Lab 5: Wheatstone Bridge Only 7 more labs to go!! The Wheatstone Bridge is a commonly used circuit for making electrical measurements. When will the current through the ammeter be equal to zero? This will happen if we choose the resistor to be just right! If we assume no current flow through the ammeter then: Since no current flows through the ammeter: This means we can divide the above equations and get this ratio:
A Where is the resistivity, L is the length and A is the cross sectional area. Remember that: Using this relationship we can rewrite: Metal Bar Ra RC Resistance Wire Lb LD
R1= 10 What is the equivalent resistance? First reduce the parallel array to one resistor. 12 V R2= 20 R4= 45 R3= 30 R1= 10 R1234 = 19.5 12 V 12 V R234= 9.5
I = 0.62 A What is the current through R1 ? R1234 = 19.5 12 V I = 0.62 A What is the voltage dropped by R1? R1= 10 6.2 V So this means that the voltage dropped by the parallel resistors is: 12 V 5.8 V R234= 9.5 Can you find the current through each resistor? Use Ohm’s Law