And also it is used to compare the EMFs of different cells. THEORY The purpose of this experiment is to measure the electromotive force (emf) and internal resistance of a dry cell. Dr. D. K. Pandey Internal resistance by potentiometer Object: To determine the internal resistance of Leclanche cell using potentiometer. A potentiometer wire is 5 m long and a potential difference of 6 V is maintained between its ends. To measure a cell's emf a potentiometer is used since in a potentiometer measurement no current is flowing. If a sensitive indicating instrument is used, very little current is drawn from the source of the unknown voltage. The calibration curve is obtained plotting voltmeter reading V on x axis and error on y axis. A cell of emf E is connected across the resistance box through key K 1. In this circuit, the ends of a uniform resistance wire R1 are connected to a regulated direct current supply VS for use as a voltage divider. (i)Calculate unknown emf of the cell. Measurement of emf of commercial cells using digital potentiometer, (Rate this solution on a scale of 1-5 below), Log into your existing Transtutors account. The emf of a cell may be defined as the terminal voltage of the cell when not under load, that is, delivering no current. The potential gradient along the length of uniform wire is 20 Vm -1. The potentiometer is first calibrated by positioning the wiper (arrow) at the spot on the R1 wire that corresponds to the voltage of a standard cell so that. A high resistance box is used in primary circuit to reduce primary current. Get it solved from our top experts within 48hrs! Save my name, email, and website in this browser for the next time I comment. The other differences between the potentiometer and the voltmeter are explained below in the comparison chart. What is potentiometer ? The balancing length is always measured from the point of higher potential. Was the final answer of the question wrong? ← Prev Question Next Question → Measurement of emf of commercial cells using... Potentiometers are the devices that measures the potential difference without consuming much power fom the system. The Potentiometer is mainly used: To compare the emfs of two primary cells; To determine the internal resistance of a primary cell; To determine the value of a high … The negative terminals of these two cells are connected to two terminals 1 and 2 of a two way key. Here the fall of the potentiometer along the length of the potentiometer wire … (ii) How does the position of balance point (J) change when the resistance R 1 is decreased? It can also use as a variable resistor in most of applications. To measure a cell's emf a potentiometer is used since in a potentiometer measurement no current is flowing. (i) What is the purpose of using high resistance R 2? The current flowing through the primary circuit is 2A and resistance per unit length is. it uses null method so that no current is drawn from cell in balanced condition, as E – Ir = V and I = 0 then V = E. hence emf measurement is more accurate. Download India's Best Exam Preparation App. V = IR and if R = 1$\Omega$ then V = I so potential difference across 1$\Omega$ resistance is equal to current through the resistance. Circuit diagram of potentiometer Potentiometer consists of a long resistive wire AB of length L (about 6m to 10 m long) made up of mangnine or constantan. © 2007-2021 Transweb Global Inc. All rights reserved. The potentiometer is adjusted by changing switch positions) until the output, as measured by a sensitive galvanometer connected from the output to the cell under test, is identical to the cell being measured. The potentiometer is a device mainly used to measure the emf of a given cell and to compare emfs of cells. Ask a Similar Question. Using a potentiometer, we can determine the emf of a cell by balancing the length. Difference Between Potentiometer & Voltmeter The potentiometer and the voltmeter both are the voltage measuring device.The significant difference between the two is that the potentiometer measures the emf of the circuit whereas voltmeter measures the end terminal voltage of the circuit. When a cell of 1.5 V emf is used in the secondary circuit, the balance point is found to be 60 cm. [CONFIRMED] JEE Main will be conducted 4 times from 2021! The error in measurement is found by comparision with readings of potentiometer. We will study here about Comparison of emf of two cells using Potentiometer, Determination of internal resistance of cell, Calibration of voltmeter, Calibration of ammeter, Measurement of small thermo emf. Other advantages of using a potentiometer are Physics 184 Experiment 3 POTENTIOMETER OBJECT: To measure the Emf of an unknown cell using a potentiometer. It employs a null method … On replacing this cell and using a cell of unknown emf, the balance point shifts to 80 cm. The positive terminal of the cell of e.m.f. The relation between potential difference, emf, and internal resistance of a cell is given by. The known emf of primary circuit must be greater than the unknown potential difference to be measured in secondary circuit. When key K 1 is opened galvanometer shows deflection at the balancing length l 1. A voltmeter cannot be used to measure the emf of a cell because a voltmeter draws some current from the cell. 2 A. The terminal voltage of a cell is the potential difference between its terminals. Since the reference voltage can be produced from an accurately calibrated voltage divider, a potentiometer can provide high precision in … Download India's Leading JEE | NEET | Class 9,10 Exam preparation app, Uses of Potentiometer | Comparison of emf of two cells using Potentiometer || Class 12, JEE & NEET, If unknown potential difference V is balanced for length $\ell$ than $V=x \ell=\left(\frac{E_{0}}{\ell_{0}}\right) l$, If the length of potentiometer wire is changed from L to L’ then the new balancing length is $\ell^{\prime}=\left(\frac{L^{\prime}}{L}\right) \ell$ If length is increased L’ > L so $l^{\prime}>l$ and if length is decreased L’ < L so $l^{\prime}
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