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Meter bridge is referred to an electrical apparatus that is conditioned to govern the resistance of a particular conductor. The meter bridge method is used in order to calculate the effective series and parallel equivalent of resistances. The meter bridge comprises a long meter bridge wire length of 1 metre, and two dissimilar segments which are left and right segments. In the left segment, the known resistance is attached, whereas in the right segment that resistance whose charge is to be measured is connected.
| Table of Content |
Key Takeaways: Meter Bridge, Resistance, Conductor, Galvanometer, Resistors in combination, Connecting wires, Battery
Aim of Experiment
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To verify the laws of the parallel combination of resistance using a meter bridge experiment.
Also Read:
| Related Articles | ||
|---|---|---|
| Kirchoffs Laws | Wheatstone Bridge | Potentiometer |
| Unit of Resistance | Difference between Resistance and Resistivity | Electrical Insulators |
Apparatus (Materials) Required for Experiments
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- Two resistance coils (carbon or wire-wound resistors)
- A Metre bridge
- A cell or battery eliminator
- Galvanometer
- A jockey
- A rheostat
- A resistance box
- A plug key
- Sandpaper
- Connecting wires (thick)
Principle
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There are two resistances R1 and R2. When connected in series, the resistance combination R1 is given by
RS= R1+R2
When connected in parallel, the resistance Rp of the combination is given below:
\(R_p = \frac{R_1R_2}{R_1 + R_2}\)
Diagram
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- When resistances are connected in parallel
- When resistances R1 and R2 are connected in parallel to one arm of a metre bridge
Procedure to Perform Experiment
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- The first and the foremost step is to step up the circuit as shown in the diagram above.
- The next step is to connect R1 and R2.
- By rotating and pressing each club, tighten all plugs in the resistance box. It makes sure a good electronic connection is made by plugs. Before making the connection, one needs to clean the ends of connections with sandpaper.
- Remove some plugs from the resistance box in order to get the suitable value of resistance R.
- By sliding the jockey between A and C ends, get a null point D on the meter bridge.
- Then, note the length of AD and DC and values of resistance R.
- Evaluate the experimental value of the equivalent resistance (parallel).
- Perform the experiment four more times to obtain more values of resistance R. Further, find out the mean value of unknown resistance.
Observation and Calculations
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| S no. | Resistance R (ohm) | Resistance from the resistance box R (ohm) | Length AD=l | Length DC=100-1 | Rp=100-1/l | Mean resistance (ohm) | |
|---|---|---|---|---|---|---|---|
| R1 only | 1 2 3 4 5 | R1 = | |||||
| R2 only | 1 2 3 4 5 | R2 = | |||||
| R1 and R2 in parallel | 1 2 3 4 5 | Rp = |
Result of Experiment
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The experimental value of Xp = ohm
The theoretical value of Xp = ohm
With the possibility of errors during the experiment, experimental and theoretical values of Rp are the same. Therefore, the law of parallel combination of resistances is verified.
Also Read: To find resistance of given wire using metre bridge
Precautions
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- Make sure all the connections and plugs are tight.
- A jockey needs to be moved gently over the meter bridge wire.
- Tighten the resistance box’s plug keys by rotating it in the clockwise direction.
- The central region of the wire should be at null points (30 cm to 70 cm).
Sources of Error
- The screws of the instrument may be loose.
- The jockey should not be pressed too hard on the meter bridge.
- On a number of occasions, resistance offered by a resistance box is not the same as indicated by it. Thus, an error can be caused in R that will cause an error in the result.
Things to Remember
- The aim of this experiment is to verify the laws of the parallel combination of resistance using a meter bridge experiment.
- There are two resistances R1 and R2. When connected in series, the resistance combination R1 is given by: RS= R1+R2.
- The experimental value of Xp = ohm.
- The theoretical value of Xp = ohm.
- The screws of the instrument may be loose.
- The jockey should not be pressed too hard on the meter bridge.
- On a number of occasions, resistance offered by a resistance box is not the same as indicated by it. Thus, an error can be caused in R that will cause an error in the result.
Also Read:
Sample Questions
Ques. Which factors affect the resistance in the meter bridge experiment? (2 marks)
Ans. The following factors affecting the resistance are:
- Length
- material
- Area of cross-section
- The temperature of the conductors'
Ques. What is the mathematical formula of Ohm’s law? (1 mark)
Ans. The mathematical formula of Ohm’s law is V = RI.
Ques. How does temperature affect the resistance of a conductor? (2 marks)
Ans. The temperature has a direct relation to the resistance of a conductor. With the increase in temperature, the resistance of the conductor also increases.
Ques. Why do we use thick connecting wires in the metre bridge experiment? (2 marks)
Ans. The sole reason for using thick connecting wire in the experiment is that they offer negligible resistance as compared to alloy wire whose resistance is not determined.
Ques. What is a metre bridge? (2 marks)
Ans. Metre bridge is a practical form of Wheatstone bridge. It is used to find the unknown resistance and resistivity of a given alloy wire.
Ques. Define Ohmic and non-ohmic resistances? (2 marks)
Ans. Resistances that adhere to Ohm’s law are known as ohmic resistances. A few examples of Ohmic resistances are Cu, Ag, Al etc.
Non-ohmic resistances are resistances that do not adhere to Ohm’s law. Some of the examples of non-ohmic resistances are diodes and transistors.
Ques. What is the definition of resistance? (2 marks)
Ans. Resistance is defined as the constant ratio of potential difference V across the ends of a conductor to the current I flowing through it. Resistance is represented by the symbol R.
Ques. What is Ohm’s law? (2 marks)
Ans. Ohm’s law is a law in electricity that states that the current (I) that is flowing through a conductor is directly proportional to the potential difference i.e. voltage (V) and is it inversely proportional to the resistance of the circuit.
Ques. Why can’t we pass a large current through the conductor during the experiment? (2 marks)
Ans. The reason why a large current can’t be passed through the conductor is that if a large current is passed then the conductor will be heated and the resistance will increase. Therefore, the graph will not remain in a straight line. This can also happen if a small current is passed for a long period of time.
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