How to Calculate Unknown Resistance Using Meter Bridge

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Updated: May 26, 2016

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A meter bridge is an apparatus used to find the resistance of a coil; you will find it as part of the tools of a physics lab.


  1. 1
    Check that the meter bridge wire is connected. If not, just connect both ends of the wire tightly. The apparatus has 5 places for the connections. All gaps for connections are found above the meter bridge wire; two on either sides and one in the middle.
  2. 2
    Imagine 5 dots plotted on a paper which are coplanar also imagine a line below it which is a little longer than the line which we can get if we join the points. The above connection is similar to this.
  3. 3
    Connect a known resistance on one side and unknown resistance on the other this fills 4/5 gaps left for connections. In the remaining gap, connect a galvanometer, high resistance and jockey all in series.
  4. 4
    Slide the jockey over the meter bridge wire and note down the reading for which you get zero deflection in galvanometer.
  5. 5
    Let it be R1 now put R2=100-R1.
  6. 6
    Similarly, calculate another reading by interchanging the known and unknown resistances in the above circuit.
  7. 7
    Let the new readings be R3 and R4 where R3 is the length obtained for zero deflection and R4=100-R3.
  8. 8
    Add R1 and R3 and divide it by two. note it down as L. calculate the average for R2 and R4 too let it be M.
  9. 9
    Repeat the above for various known resistance values. Each time you can calculate the unknown resistance using the formula:unknown resistance(a)=known resistance(b)*L/M. The value is found to be the same for all values of known resistance.

Community Q&A

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  • Question
    How can I calculate the resistance of coiled wire?
    Community Answer
    Coiled wire is the unknown resistance which is calculated using Wheatstone bridge or Carl Froster bridge.
  • Question
    What causes the errors which make the resistance of unknown variables?
    Community Answer
    The incorrect reading at the meter scale with respect to null deflection of the galvanometer causes variable in the resistance. Also, the supply of current for longer time overheats the galvanometer and its internal resistance varies, which makes the resistance variable.
  • Question
    How do I calculate the unknown resistance of wire, given 1 ohm as a fixed resistance, using a meter bridge?
    Community Answer
    By using a meter bridge circuit. The known standard resistor of 1 ohm will be connected on the left hand gap of the meter bridge, and the unknown resistance will be connected on the right hand gap of the meter bridge. Then, when the balance point is obtained, the unknown resistance can be calculated using the meter bridge formula: l/100-l = 1/R
  • Question
    How do I draw a diagram to determine the resistance using a meter bridge?
    Community Answer
    Formula: P=Q(L1/L2). Let P be the known resistance, and Q be the unknown resistance. Enter the length AJ in L1, and enter the length b/w JC in L2. Enter the appropriate values in the above formula and do the math.
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    Categories: Electromagnetism

    In other languages:

    Русский: определить неизвестное сопротивление при помощи измерительного моста

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