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How long does it take for the batter to lose its charge?

  • #1

Homework Statement


The two headlights of a car sonsume a total power of 120 W. A driver parks the car but leaves the lights on. The 12-V battery is rated at 95 A * h.

Homework Equations


P=IV
V=IR

The Attempt at a Solution


I don't know any equation that associates this with time. [/B]
 

Answers and Replies

  • #2
gneill
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Hi pandamonium, Welcome to Physics Forums.

Can you determine the amount of current drawn by the lights?
 
  • #3
Since power and voltage is given, we use P=IV to solve for the current I, correct ?
 
  • #4
Hi pandamonium, Welcome to Physics Forums.

Can you determine the amount of current drawn by the lights?
Since power and voltage is given, we use P=IV to solve for the current I, correct ? And thanks!
 
  • #5
gneill
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20,792
2,770
Since power and voltage is given, we use P=IV to solve for the current I, correct ? And thanks!
That's right. What value do you get for the current?
 
  • #6
That's right. What value do you get for the current?
I got I=10.
 
  • #7
gneill
Mentor
20,792
2,770
I got I=10.
Okay, now take a closer look at the units of the battery capacity. How long will you have to draw 10 A to equal that capacity?
 
  • #8
Okay, now take a closer look at the units of the battery capacity. How long will you have to draw 10 A to equal that capacity?
Oh, since 95 is the total charge that the battery can produce before failing, I can divide 95/10 to get the time before it fails, correct ?
 
  • #9
gneill
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20,792
2,770
Oh, since 95 is the total charge that the battery can produce before failing, I can divide 95/10 to get the time before it fails, correct ?
Yes. You can check your logic by working with the units.
 
  • #10
Yes. You can check your logic by working with the units.
Thanks for all the help ! I really appreciate it c:
 

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