When the lights of a car are switched on, an ammeter in series with them reads 1

Question

When the lights of a car are switched on, an ammeter in series with them reads 10.2 A and a voltmeter connected across them reads 12.0 V (see the figure). When the electric starting motor is turned on, the ammeter reading drops to 8.05 A and the lights dim somewhat. If the internal resistance of the battery is 0.0391 and that of the ammeter is negligible, what are (a) the emf of the battery and (b) the current through the starting motor (in A) when the lights are on? Lights Starting motor w (a) Number Units 3 (b) Number Units

Explanation / Answer

(a) The emf of the battery is

= V + i*r

= 12 + 10.2*(0.0391)

= 12.398 V

(b) The voltage of the light is

V ' = i *Rlight

= (8.05)(12/ 10.2)

= 9.470 volts
  
The emf is

= V ' + ( i motor + 8.05) r

i motar = ( - V ' / r) - 8.05
  
= (12.39 - 9.47 / 0.0391) - 8.05

= 66.63 A

Related Questions

Navigate

• Browse (All)
• Browse W
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.