3.15 (a) Six lead-acid type of secondary cells each of emf 2.0 V and internal resistance 0.015 Ω are joined in series to provide a supply to a resistance of 8.5 Ω. What are the current drawn from the supply and its terminal voltage?

(b) A secondary cell after long use has an emf of 1.9 V and a large internal resistance of 380 Ω. What maximum current can be drawn from the cell? Could the cell drive the starting motor of a car?

<p><strong>3.15 (a) </strong>Number of secondary cells, n = 6</p><p>emf of each secondary cell = 2 V</p><p>Internal resistance of each secondary cell, r = 0.015 Ω</p><p>Resistance of the resistor, R = 8.5 Ω</p><p>Current drawn from the supply, I is given as I =&nbsp;<span title="Click to copy mathml"><math><mfrac><mrow><mrow><mi>T</mi><mi>o</mi><mi>t</mi><mi>a</mi><mi>l</mi><mi></mi><mi>v</mi><mi>o</mi><mi>l</mi><mi>t</mi><mi>a</mi><mi>g</mi><mi>e</mi></mrow></mrow><mrow><mrow><mi>R</mi><mo>+</mo><mi>t</mi><mi>o</mi><mi>t</mi><mi>a</mi><mi>l</mi><mi></mi><mi>i</mi><mi>n</mi><mi>t</mi><mi>e</mi><mi>r</mi><mi>n</mi><mi>a</mi><mi>l</mi><mi></mi><mi>r</mi><mi>e</mi><mi>s</mi><mi>i</mi><mi>s</mi><mi>t</mi><mi>a</mi><mi>n</mi><mi>c</mi><mi>e</mi></mrow></mrow></mfrac></math></span></p><p>=&nbsp;<span title="Click to copy mathml"><math><mfrac><mrow><mrow><mn>6</mn><mi></mi><mo>×</mo><mn>2</mn></mrow></mrow><mrow><mrow><mn>8.5</mn><mo>+</mo><mn>6</mn><mi></mi><mo>×</mo><mn>0.015</mn></mrow></mrow></mfrac></math></span>&nbsp;= 1.396 A</p><p><strong>(b) </strong>Terminal voltage = I&nbsp;<span title="Click to copy mathml"><math><mo>×</mo><mi>R</mi></math></span>&nbsp;= 1.396&nbsp;<span title="Click to copy mathml"><math><mo>×</mo><mn>8.5</mn></math></span>&nbsp;= 11.87 V</p><p>After long use emf = 1.9 V</p><p>Internal resistance of the cell, r = 380 Ω</p><p>Maximum current can be drawn =&nbsp;<span title="Click to copy mathml"><math><mfrac><mrow><mrow><mn>1.9</mn></mrow></mrow><mrow><mrow><mn>380</mn></mrow></mrow></mfrac></math></span>&nbsp;= 5&nbsp;<span title="Click to copy mathml"><math><mo>×</mo><msup><mrow><mrow><mn>10</mn></mrow></mrow><mrow><mrow><mo>-</mo><mn>3</mn></mrow></mrow></msup></math></span>&nbsp;A</p><p>No, the cell cannot drive the starter motor of the car as it requires high current.</p>

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