A potentiometer wire of 10 m length and 10 ohm total resistance is connected to a 2 V accumulator. A cell of EMF 1 V gives null point at:

A meter bridge works on the principle of:

A potentiometer measures EMF without drawing current because:

In a potentiometer, the EMF of a cell is proportional to:

Internal resistance of a cell using potentiometer: balance length $l_1$ (open circuit) and $l_2$ (with resistance $R$ across cell). Internal resistance $r$ is: <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 360 160" style="max-width:360px;background:#faf9f5"> <title>Potentiometer measurement of internal resistance: open circuit l1, with R gives l2</title> <!-- Wire --> <line x1="30" y1="30" x2="330" y2="30" stroke="#14140f" stroke-width="2.5"/> <text x="30" y="22" font-size="8" fill="#14140f">A</text> <text x="330" y="22" font-size="8" fill="#14140f">B</text> <!-- Two balance points --> <line x1="210" y1="30" x2="210" y2="60" stroke="#c6613f" stroke-width="1.2" stroke-dasharray="3,2"/> <circle cx="210" cy="30" r="3" fill="#c6613f"/> <text x="215" y="22" font-size="8" fill="#c6613f">l_{1}</text> <line x1="150" y1="30" x2="150" y2="60" stroke="#788c5d" stroke-width="1.2"/> <circle cx="150" cy="30" r="3" fill="#788c5d"/> <text x="155" y="22" font-size="8" fill="#788c5d">l_{2}</text> <!-- Cell being measured --> <line x1="30" y1="30" x2="30" y2="100" stroke="#14140f" stroke-width="1"/> <line x1="30" y1="100" x2="50" y2="100" stroke="#14140f" stroke-width="1"/> <!-- Cell symbol --> <line x1="50" y1="92" x2="50" y2="108" stroke="#14140f" stroke-width="2"/> <line x1="58" y1="95" x2="58" y2="105" stroke="#14140f" stroke-width="1"/> <text x="54" y="88" text-anchor="middle" font-size="7" fill="#14140f">ε,r</text> <!-- Internal r --> <line x1="58" y1="100" x2="80" y2="100" stroke="#14140f" stroke-width="1"/> <!-- External R (with switch) --> <rect x="90" y="90" width="40" height="18" rx="3" fill="#faf9f5" stroke="#788c5d" stroke-width="1"/> <text x="110" y="103" text-anchor="middle" font-size="8" fill="#788c5d">R</text> <line x1="130" y1="100" x2="180" y2="100" stroke="#14140f" stroke-width="1"/> <!-- Connect to jockey point --> <line x1="180" y1="100" x2="180" y2="60" stroke="#14140f" stroke-width="1"/> <!-- Galvanometer --> <circle cx="180" cy="75" r="8" fill="#faf9f5" stroke="#788c5d" stroke-width="1"/> <text x="180" y="78" text-anchor="middle" font-size="7" fill="#788c5d">G</text> <text x="180" y="150" text-anchor="middle" font-size="9" fill="#14140f">r = R(l_{1}−l_{2})/l_{2}</text> </svg>