A voltmeter cannot be used to measure the emf of a cell because a voltmeter draws some current from the cell. A standard cell is connected between the terminals A and B of potentiometer wire with a rheostant Rh and a key K in series. 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. If galvanometer shows no deflection for some $R_{1}$ then potential difference across $R_{1}$ is $V=E_{0}=I R_{1}$ or $|=E_{0} / R_{1}$, If balancing length for small thermo emf E is $\ell$ then $E=x \ell=\frac{E_{0}}{R_{1}} \cdot \frac{R}{L} \ell$. (Hide this section if you want to rate later). Complete Physics Revision Series by Saransh Sir (AIR 41 in IIT-JEE), To determine the internal resistance of a primary cell, To determine the value of a high resistance, Cells Connected in Series, parallel and Mixed, Comparison of emf of two cells using Potentiometer, Determination of Internal Resistance of Cell, Determination of unknown EMF or Potential Difference, Kelvin Bridge – Definition and Diagram || Current Electricity Class 12, JEE & NEET, JEE Main Previous Year Questions Topicwise, JEE Main 2021 – Exam Pattern, Important Dates, Syllabus. If the potential difference across 10 ohm coil is balanced at 2.5 m then find current flowing through the coil. The other differences between the potentiometer and the voltmeter are explained below in the comparison chart. 2 mA. Was the final answer of the question wrong? E 1 is connected to end A and a negative terminal is … Answered February 16, 2017. A high resistance box is used in primary circuit to reduce primary current. The emf of a cell may be defined as the terminal voltage of the cell when not under load, that is, delivering no current. Potentiometer works on the principle that when a constant current flows through a wire of uniform cross sectional area, potential difference between its two points is directly proportional to the length of the wire between the two points. So, E = k Find E1/E2. (a) State the Principle of working of a potentiometer. The positive terminal of the cell of e.m.f. The known emf of primary circuit must be greater than the unknown potential difference to be measured in secondary circuit. If the driver cell of emf 5V is replaced with a cell of 2V keeping all other factors constant then potential drop along AB is 0.2Volt. And also it is used to compare the EMFs of different cells. The current through R or 1$\Omega$ coil is measured by, ammeter () and calculated by potentiometer as $V^{\prime}=I^{\prime} \times 1 \Omega=x \ell_{1}=\left(\frac{E_{0}}{\ell_{0}}\right) \ell_{1}$. The error in measurement is found by comparision with readings of potentiometer. The potentiometer is used as a precision divider. 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. 33.A potentiometer wire of length lm is connected to a driver cell of emf 3 V as shown in the figure. Two cells of emfs ε1 and ε2 to be compared are connected to A where the positive terminal of standard cell was connected. Since the balance point can't be obtained on the potentiometer if the fall of potential along the potentiometer wire is due to the auxiliary battery is … Sol. Physics 184 Experiment 3 POTENTIOMETER OBJECT: To measure the Emf of an unknown cell using a potentiometer. For determination of current we use a coil of standard resistance. 0 A. C. 2 A. Internal Resistance of a Cell Using Potentiometer Experiment. 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. Here the fall of the potentiometer along the length of the potentiometer wire … A voltmeter cannot be used to measure the emf of a cell because a voltmeter draws some current from the cell. Ask a Similar Question. 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. Reading of potentiometer is accurate because during taking reading it does not draw any current from the circuit. The emf of cell will be measured accurately. 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}