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Car battery questions

  1. Sep 27, 2007 #1
    hi, i got this hwk today and i've answered the questions i can do, can you check the answers i have done, and also help me with the ones i can't do.
    thank you so much!
    x

    1. A car battery can supply 6 000 000 J to a car headlamp while delivering 500 000 C of charge through the headlamp. Calculate the potential difference across the headlamp.
    PD (V) = Energy Supplied / Charge that flows
    = 600 0000J / 500 000 C
    = 12V


    2. A car battery supplies a power of 60W to a car headlamp using a current of 5.0 A. Calculate the potential difference across the headlamp.
    PD (V) = Power Supplied / Current
    = 60 W / 5.0 A
    = 120 V


    3. If questions 1 and 2 apply to the same battery, under the same conditions of use, for how long was the battery in use?

    4. A 120 W bulb for a projector could be manufactured so that it either operates on 240 V mains or on a 20 V transformer. How much current would be supplied by each supply?.
    240 V mains current supplied -> 120 W / 240 V = 0.5 A
    20 V transformer supplied -> 120 W / 20 V = 6 A


    5a) A 4600 W electric motor is to operate from a 230 V mains supply. What current will be required?
    Power / P.D = Current -> 4600 W / 230 V = 20 A

    b) Why might more than this current be needed in practice to obtain this output power?

    6. A current of 3.2 mA passes through a circuit component for 300 s. The PD across the component is 12 V. How much energy is supplied to the component?
    Charge = Current x Time
    = 0.0032 x 300
    = 0.96 C
    PD x Charge = Energy -> 12 x 0.96 = 11.52 W


    7. During one use of a hairdrier the following quantities are measured. Determine the unknown quantities. Measured quanitites: PD = 240 V, power = 1200 W, time = 600 s. Unknown quantities: current, charge, energy.
    Current = Power supplied / PD = 1200 W / 240 V = 5A
    Charge = Current x Time = 5 A x 600 s = 3000 C
    Energy = Power x Time = 1200 W x 600 s = 720000 W


    b) Why might more than this current be needed in practice to obtain this output power?
     
    Last edited: Sep 27, 2007
  2. jcsd
  3. Sep 27, 2007 #2
    In question 2, you seem to have misplaced a decimal point.

    You seem to be generally doing things correctly, but some of these are rather strange questions.
     
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