Meter Bridge for IIT JEE

There are several things that happen in day-to-day life that amazes us. There are numerous experiments that show creative ways to use things and build newer things from them. Meter Bridge is one of those few interesting experiments in science that fills us with curiosity and amazement. In this article, we will be learning more about the concept of the Meter Bridge in detail. 

What is Basically a Meter Bridge?

A meter bridge is observed to be a simple form of potentiometer that is used in science laboratories in schools and colleges. This device is very useful in the determination of the principle of measurement of resistance by potentiometric means.

Here in this device, a wire of an unknown resistance is used and is connected to a galvanometer by the use of a slider. When the reading of the galvanometer is zero, then the ratio between the wire length to the right and left sides of the slider becomes equivalent to the ratio of an identified and unidentified resistor in a parallel form of a circuit.

A Meter Bridge is popularly called a slide wire bridge. The Wheatstone meter bridge was invented in the year 1833 by a famous scientist Samuel Hunter Christie which was later enhanced and popularized by scientist Charles Wheatstone in the year 1843.

A slide wire bridge is basically a type of resistance measuring device that is used in the form of a Wheatstone bridge. It consists of a spiral or a straight spiral-shaped wire that is divided into two parts by using a sliding contact that forms the complete or identified regions of head-to-head arms of the meter bridge.

Meter Bridge is also termed as a Wheatstone's meter bridge. It is a device that is useful in identifying the unidentified resistance of any wire in a Wheatstone bridge and performing a comparison between two unknown resistors.

The apparatus of a meter bridge comprises connecting wires, a one-way key, a scale, an unknown Resistor, a Resistance Box or a known resistor, a jockey, and a Galvanometer. This entire experiment is carried out to measure the specific resistance of the material of the wire. The length of the wire that is used in performing this experiment is one meter.

Let us see how to do a connection of this circuit:

• We use a resistance box as R and an unidentified resistance as “S” to connect across the 2 gaps of metallic copper strips. Now connect one of the ends of the galvanometer device to the mid lead of a metallic strip. 

• This strip is placed in between the two copper strips with the shape of L. Now you need to connect the other end of a galvanometer to a jockey. This jockey is later used to easily slide on the wire of the bridge. A jockey is basically a metallic rod that has one of its ends as the edge of a knife.

• To calculate the unknown resistance of a wire, you will be required to connect all the above devices and the wires in the correct way. This will form a circuit. In the starting, the meter reading of the galvanometer will be zero. In other words, it does not show any deflection. 

• At this time, you need to measure the length of the unknown resistor. Let us name this length L1. Once you do this, you will need to adjust the resistance value in the resistor. The value of the variable resistor can change with the application of the voltage to the circuit. Now slide the jockey throughout the wire. 

• Now measure the wire length, when the voltage is applied through the circuit. The galvanometer shows null deflection. Let us name this length L2. Now once you get both these lengths, you can use the Wheatstone bridge principle to find the unidentified resistance of a Meter Bridge. 

• This unknown resistance wire has a uniform cross-sectional area such that L1 + L2 = 100. This wire is properly fixed on a wooden based block. The material with which this wire is made is manganin or constantan.

• With technological advancement, nowadays it has become possible to perform different types of measurements by using sophisticated machines and tools. However, still today, the wheat bridge is an authentic means to calculate the resistance of an electric circuit (to even the nearest milli-ohms with complete accuracy).

Assuming that L1 = L = 100 – L

Now, unidentified resistance “X” of a given wire: X = R * L2 / L1 = R (100-L) / L

The specific resistance (R) of the wire material is obtained by the above relation as (3.14) * (r *2 X) / L 

Here: r is the radius of the wire, and l is the length of the wire.

To find the correctness of the output, you can interchange or swap the placement of the unknown as well as known resistance in the bridge. If your bridge is symmetrical and working properly and rightly, then you will be getting the same value of resistance in this case too. If you get different values in both cases, then the bridge is not symmetrical. 

Why is Manganin or Constant Chosen as the Material of the Wire?

To perform a meter bridge experiment, the wire is made up of manganin or constantan because of its high resistivity or specific resistance. The material constant was started to be used in performing experiments by Edward Weston in the year 1892. Foil made up of Manganin is mostly used in the formation of resistors, especially ammeter shunts. This is because of the virtually 0 temperature co-efficient of the value of the resistance and its longer-term stability.

Why does it make sense to use Copper Wires in performing an Experiment?

Thick strips of copper are used in this bridge as copper is considered to be a favorable conductor of electricity. The reason for using broad metal strips in the Meter Bridge is to lessen the amount of error measured in the unknown resistance’s value.

Why was this Bridge Experiment called a Meter Bridge?

The reason why this bridge is called the Meter Bridge is because of the fact that it works on the Wheatstone bridge’s principle. So, people also popularly call it Wheatstone's meter bridge. Another thing is that the wire length used in this circuit is 1 meter, so it has got its name as a meter bridge.

What kinds of End Errors are Reported in a Meter Bridge?

One of the commonest forms of errors that are reported in the meter bridge experiment is the shifting of 0 on the galvanometer scale at varying points and the stray resistance that results in the formation of end error in the wire of the meter bridge wire.

The basic reason behind this error is the non-uniformity of the wire. End corrections are projected by the inclusion of known resistances at the two ends and then locating the null point.

What is Measured as a Null Point in a Meter Bridge?

There is a null point observed in the case of a meter bridge experiment. This “null point” is located at a distance of forty centimeters from point A. On application of resistance of magnitude 12 ohm to the circuit in parallel to the variable resistance, a null point is formed and measured at 50.0 cm from A. 

What do you mean by Balancing Length in a Meter Bridge?

Balancing length is an important concept in a meter bridge experiment. The value of balancing length “l” is seen to remain constant when the radius of the meter bridge wire gets doubled and keeps the cross-section area of the wired uniform. This happens due to the relation R/X = l/(100−l), being independent of the cross-section area of the wire. Here, X is an unknown resistance.

What are the Practical Applications of a Wheatstone Meter Bridge?

The Wheatstone bridge is one of the most popular bridges in the history of science. There are several different applications of this bridge in the invention of various new scientific principles. The use of this bridge includes a thermistor, strain gauge, light detector, potentiometer, etc. Wheatstone bridge also has its significance in an operational amplifier due to its ability to measure and magnify the tiny changes that occur in resistors.

In what ways does a Potentiometer Differ from a Meter Bridge?

Both potentiometer and a meter bridge are widely used devices in the calculation of several scientific theories and inventions. They have a huge significance in science. A Meter Bridge is a kind of electric device that assists in the measurement of an unidentified resistance.

On the other hand, a potentiometer is also an electric device that is used for the measurement of the internal resistance and the EMF or electromotive force of cells. It helps in the comparison of emf of two cells along with a potential difference that forms between 2 points in a given electric circuit. However, it has been found that the accuracy is greater in a potentiometer because of the use of a longer length of resistance wire.

A potentiometer is a three-terminal resistor with a sliding or turning contact that frames a movable voltage divider. If by some stroke of good luck two terminals are utilized, one end and the wiper, it goes about as a variable resistor or rheostat.

The estimating instrument called a potentiometer is basically a voltage divider utilized for estimating electric potential (voltage); the part is an execution of a similar rule, henceforth its name.

Potentiometers are normally used to control electrical gadgets, for example, volume controls on sound gear. Potentiometers worked by a system can be utilized as position transducers, for instance, in a joystick. Potentiometers are seldom used to straightforwardly control huge power (in excess of a watt), since the power scattered in the potentiometer would be similar to the power in the controlled burden.

Advanced Potentiometer

An advanced potentiometer (regularly called digit) is an electronic part that impersonates the elements of simple potentiometers. Through advanced information flags, the opposition between two terminals can be changed, similarly as in a simple potentiometer. There are two principle practical sorts: unpredictable, which lose their set position in the event that power is taken out, and are normally intended to initialize at the base position, and non-unstable, which hold their set position utilizing a capacity system like blaze memory or EEPROM.

The use of a digit is undeniably more perplexing than that of a basic mechanical potentiometer, and there are numerous impediments to notice; all things considered, they are generally utilized, frequently for manufacturing plant change and adjustment of hardware, particularly where the restrictions of mechanical potentiometers are hazardous. A digit is by and large safe with the impacts of moderate long haul mechanical vibration or ecological tainting, similarly to other semiconductor gadgets, and can be gotten electronically against unapproved altering by securing the admittance to its programming inputs by different means.

In gear that has a chip, FPGA, or another useful rationale that can store settings and reload them to the "potentiometer" each time the hardware is fueled up, an increasing DAC can be utilized instead of a digit, and this can offer a higher setting goal, less float with temperature, and more functional adaptability.

Layer Potentiometers

A layer potentiometer uses a conductive film that is twisted by a sliding part to contact a resistor voltage divider. Linearity can go from 0.50% to 5% contingent upon the material, plan, and assembling process. The recurrent exactness is regularly between 0.1 mm and 1.0 mm with a hypothetically boundless goal. The help life of such potentiometers is consistently 1 million to 20 million cycles depending upon the materials used during the gathering and the invitation technique; contact and contactless (attractive) techniques are accessible (to detect position). A wide range of material varieties is accessible like PET, FR4, and Kapton. Layer potentiometer makers offer straight, rotational, and application-explicit varieties. The straight structures can go from 9 mm to 1000 mm long and the pivoting versions range from 20 to 450 mm in width, with each having a height of 0.5 mm. Layer potentiometers can be utilized for position sensing.

For contact screen gadgets utilizing resistive innovation, a two-layered film potentiometer gives x and y organizes. The top layer is dainty glass separated near an adjoining internal layer. The underside of the top layer has a straightforward conductive covering; the outer layer of the layer underneath it has a straightforward resistive covering. A finger or pointer distorts the glass to contact the hidden layer. Edges of the resistive layer have conductive contacts. Finding the contact point is finished by applying a voltage to inverse edges, leaving the other two edges briefly detached. The voltage of the top layer gives one direction. Separating those two edges, and applying a voltage to the next two, previously detached, gives the other direction. Exchanging quickly between sets of edges gives regular position refreshes. A simple-to-computerized converter yields information.

The benefits of such sensors are that the main five associations with the sensor are required, and the related gadgets are relatively straightforward. Another is that any material that pushes down the top layer over a little region functions admirably. A weakness is that adequate power should be applied to connect. One more is that the sensor requires infrequent adjustment to match the contact area to the fundamental showcase. (Capacitive sensors require no alignment or contact power, just the vicinity of a finger or other conductive article. Nonetheless, they are fundamentally more perplexing.)

Applications

Potentiometers are seldom used to straightforwardly control huge measures of force (in excess of a watt or somewhere in the vicinity). Rather they are utilized to change the degree of simple signs (for instance volume controls sound hardware), and as control inputs for electronic circuits. For instance, a light dimmer uses a potentiometer to control the exchanging of a TRIAC thus in a roundabout way to control the brilliance of lights.

Client impelled potentiometers are broadly utilized as client controls and may control an extremely wide assortment of gear capacities. The far-reaching utilization of potentiometers in buyer hardware declined during the 1990s, with rotational steady encoders, up/down press buttons, and other advanced controls now more normal. Anyway, they stay in numerous applications, for example, volume controls and position sensors.

Sound Control

The 'log pot', that is, a potentiometer has an obstruction, tighten, or, "bend" (or law) of a logarithmic (log) structure, is utilized as the volume control in sound power enhancers, where it is likewise called a "sound shape pot", on the grounds that the adequacy reaction of the human ear is around logarithmic. It guarantees that on a volume control checked 0 to 10, for instance, a setting of 5 sounds abstract half as clearly as a setting of 10. There is additionally an enemy of log pot or opposite sound shape which is basically the converse of a logarithmic potentiometer. It is quite often utilized in a ganged design with a logarithmic potentiometer, for example, in a sound equilibrium control.

Potentiometers utilized in mix with channel networks go about as tone controls or equalizers. In sound frameworks, the word direct is once in a while applied in a befuddling method for portraying slide potentiometers due to the straight-line nature of the actual sliding movement. The word straight when applied to a potentiometer paying little mind to be a slide or rotating type, depicts a direct relationship of the pot's position versus the deliberate worth of the pot's tap (wiper or electrical result) pin.