Problem #11 (20 points): When the lights of a car are switched on, am ammeter in

Question

Problem #11 (20 points): When the lights of a car are switched on, am ammeter in series with them reads 10.0 A and a voltmeter across them reads 12.0 V. When the starter motor is turned on too, the ammeter reads 8.00 A and the lights dim somewhat. If the internal resistance of the battery is 0.0500 and the resistance of the ammeter is negligible, what are (a) the em of the battery and (b) the current through the starter motor when the lights are on? Hint: remember what serial and parallel mean. Take what you know and start filling in the blank bits you don't! Don't just start making loops and equations, this one's easier than that.

Explanation / Answer

a) The emf is gven by

          = V + i r = 12+ 10(0.05)

           = 12.5V

b)The voltage of the light is

       V ' = i Rlight= (8)(12/ 10) = 9.6 volts

      The emf is

          = V ' + ( i motor + 8) r

          imotar = ( - V ' / r) - 8

                     = (12- 9.6 / 0.05) - 8

                     = 50A

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