Content Writer-SME | Updated On - Oct 24, 2024
Meter Bridge also called slide wire bridge works on the principle of the Wheatstone bridge. This is a very important concept covered in the chapter Current Electricity. Some of the important Meter Bridge questions are being covered in this article which is based on the CBSE Class 12 Physics Syllabus.
Meter bridge questions mainly involve calculation of an unknown resistance in a current carrying conductor. The following diagram explains how the meter bridge can be used to evaluate the unknown resistance in an electrical circuit:
Meter Bridge Circuit Diagram
The meter bridge can be used to calculate the specific resistance of a wire and this can be estimated as:
The unknown resistance \(X=\)\(R\times \frac{I_2}{I_1}\) \(=\)\(R\times \frac{100-I}{I}\)
The specific resistance of the wire material is equals to \(3.14\times \frac{r_2X}{I}\)
Where,
r = the radius of the cable
l = length of the wire.
Read More: NCERT Solutions Class 12 Physics Current Electricity
Meter Bridge Class 12 Important Questions
Q.1 What is the principle used in a meter bridge? (2 marks)
A.1 Meter bridges work on the principle of the Wheatstone bridge. The Wheatstone bridge is based on null deflection wherein there is no current flow in the middle of the circuit when the resistance ratios in the one arm are equal to the other arm of the bridge.
Q.2 What is the use of jockey in a meter bridge? (3 marks)
A.2 The jockey in a meter bridge facilitates the sliding on the bridge wire. It is a metal rod whose one end is like a knife edge. The value of the resistance in the box can be adjusted and the jockey is slid along the wire. This process is repeated until the galvanometer indicates zero or zero deflection. When using jockeys in a meter bridge the accuracy rate at the midpoint (balance point) of the bridge wire becomes particularly high.
Q.3 What are the commonly used materials in a meter bridge? (2 marks)
A.3 Meter bridge is highly sensitive and hence needs to have materials that have a low-temperature coefficient of resistivity. Thus, alloys like maganin, constantan, or nichrome are predominantly used in the meter bridge wires.
Q.4 What is the null point in a meter bridge? (1 mark)
A.4 The null point in a meter bridge is at the middle point of the wire. In meterbridge questions of physics, the null point is also called as balanced point.
Read More:
Q.5 Why is Leclanche cell used in a meter bridge? (2 marks)
A.5 Leclanche cells are easily manufactured and have greater e.m.f. as compared to Daniel Cell. This makes them the cell of choice in a meter bridge. Apart from this, it can also be utilised in potentiometer. The positive and negative and terminals of the Leclanche cell are usually connected to point A and point C of the meter bridge.
Q.6 What is the length of the meter bridge wire? Why are these wires not made of Copper? (2 marks)
A.6 In all meterbridge questions the length of meter bridge wire is always fixed which is equals to 100 cm. The meter bridge wire is not made of copper due to its low resistance and high temperature resistance coefficient.
Q.7 What is the range of the meter scale and the least count of the meter bridge? (2 marks)
A.7 A meter scale has graduations at 1mm spacing and this is the smallest division in the scale. In the case of meter bridge questions, the least count is always 1 mm.
Q.8 A resistance wire connected in the left gap of the meter bridge balances a 10 Ω resistance in the right gap. This happens at a point where the bridge wire is divided in the ratio of 3:2. Assuming the length of the wire to be 1.5 m, calculate the length of the 1 Ω resistance wire? (3 marks)
A.8 In this meter bridge question the ratio of wires is given as 3:2
Therefore, Let \(\frac{R}{S} = \frac{3}{2}\)
S= 10 Ω
Calculating \(R= \frac{3}{2}\times 10\)
R= 15 Ω
Length of the 1 Ω wire \(=\frac{1.5}{15}\)
=0.1 m
Q.9 X and Y are two resistances in the two gaps of the meter bridge. The null point is obtained at the point where the wires divide in the ratio of 2:3. When each of the resistances is increased by 3Ω, the null point divides the worse in the ratio of 5:6. What are the values of the resistances X and Y? (3 marks)
A.9 In this meter bridge question, by balancing the Wheatstone bridge in the initial position, we get
\(\frac{X}{2}=\frac{Y}{3}\)
Thus,
3X = 2Y – (1)
In the second case, \(\frac{X+30}{5}=\frac{Y+30}{6}\)
6X +180= 5Y + 150 – (2)
Substituting, we get
4Y+180=5Y+150
Y=30Ω
From (1)
3X=2Y
X= 3
Therefore, X=20 Ω and Y= 30Ω
Q.10 What are the sources of error in a meter bridge? (3 marks)
A.10 Some of the error sources in meter bridge questions are as follows:
- Loose screws in the instrument
- Non-uniform diameter of wire
- Backlash error in the screw gauge
Q.11 What is the importance of meterbridge in physics? (2 marks)
A.11 As we know meterbridge works on the principle of balanced wheatstone bridge. Thus, the application can best be seen in the calculation of the unknown resistance of a coil in meterbridge questions .
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