The other differences between the potentiometer and the voltmeter are explained below in the comparison chart. The potential gradient along the length of uniform wire is 20 Vm -1. 2 mA. (i) What is the purpose of using high resistance R 2? If the potential difference across 10 ohm coil is balanced at 2.5 m then find current flowing through the coil. Hence V=IR = E-Ir The emf of cell will be measured accurately. 0 mA. $\frac{E_{1}+E_{2}}{E_{1}-E_{2}}=\frac{6}{2}$ or $\frac{E_{1}}{E_{2}}=\frac{2}{1}$, Keeping $\mathrm{K}_{1}$ open the balancing length $\ell_{1}$ gives, Keeping $K_{1}$ closed the balancing length $\ell_{2}$ for some resistance R gives potential difference so V = $x \ell_{2}$, Internal resistance $r=\frac{E-V}{V} \quad R=\frac{x \ell_{1}-x \ell_{2}}{x \ell_{2}}$, $R=\left(\frac{\ell_{1}-\ell_{2}}{\ell_{2}}\right) R$. (b) Figure shows the circuit diagram of a potentiometer for determining the emf ‘ ε ’ of a cell of negligible internal resistance. The potentiometer is a device mainly used to measure the emf of a given cell and to compare emfs of cells. The potentiometer is used as a precision divider. A cell of emf E is connected across the resistance box through key K 1. where E1 and E2 are EMFs of two cells, l1 and l2 are the balancing lengths when E1 and E2 are connected to the circuit respectively and φ is the potential gradient along the potentiometer wire. (a) State the Principle of working of a potentiometer. On replacing this cell and using a cell of unknown emf, the balance point shifts to 80 cm. THEORY The purpose of this experiment is to measure the electromotive force (emf) and internal resistance of a dry cell. POTENTIOMETER OBJECT: To measure the Emf of an unknown cell using a potentiometer. 0.2 $\Omega / m$. Therefore the measurement of cell’s emf will not be accurate To measure a cell’s emf use of a potentiometer is preferred since in potentiometer-measurement no current flows through the cell. 33.A potentiometer wire of length lm is connected to a driver cell of emf 3 V as shown in the figure. E1 /E2 = φ l1 /φ l 2 = l1 /l 2 These potentiometers are used in huge quantities in the manufacture of electronics equipment that provides a way of adjusting electronic circuits so that the … The current flowing through the primary circuit is 2A and resistance per unit length is. At t = 0, no current flows through R 1 and R 3. A potentiometer is an instrument for measuring voltage or 'potential difference' by comparison of an unknown voltage with a known reference voltage. The terminal voltage of a cell is the potential difference between its electrodes. It employs a null method … Aim: To determine the internal resistance of a given primary cell using cell using potentiometer .. Sol. 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. Save my name, email, and website in this browser for the next time I comment. A cell is characterised by its emf ε. cell therefore potentiometer is preferred to measure the emf of a cell than a voltmeter because emf of a cell is equal to terminal potential difference when no current flows from the cell. For determination of current we use a coil of standard resistance. (Hide this section if you want to rate later). Potentiometer can be used to measure the internal resistance of the cell. 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 … Using a voltmeter it is possible to measure only the potential difference between the two terminals of a cell, but using a potentiometer we can determine the value of emf of a given cell. Browse More Topics Related to Potentiometer: Let $E_{1}$ emf be balanced at length $\ell_{1}$ and $E_{2}$ emf be balanced at length $\ell_{2}$ then, $E_{1}=x \ell_{1}$ and $E_{2}=x \ell_{2}$ so $\frac{E_{1}}{E_{2}}=\frac{l_{1}}{l_{2}}$, If two cells joined in series support each other, If two cells joined in series oppose each other. When current is drawn from a cell, there is a movement (flow) of ions in the electrolyte between the electrodes of the cell. (b) Potentiometer works on the principle that when a constant current flows 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. An instrument to measure potentiometer difference or emf of a cell. Hence we measure the emf. Two cells of emf $E_{1}$ and $E_{2}$ connected to support and oppose each other are balanced over $\ell_{1}$ = 6m and $\ell_{2}$ = 2m. Since the reference voltage can be produced from an accurately calibrated voltage divider, a potentiometer can provide high precision in … If a sensitive indicating instrument is used, very little current is drawn from the source of the unknown voltage. Reading of potentiometer is accurate because during taking reading it does not draw any current from the circuit. Internal Resistance of a Cell Using Potentiometer Experiment. 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}