How long does it take electrons to get from a car battery to the starting motor? Assume the current is 300 A and the electrons travel throug

Question

How long does it take electrons to get from a car battery to the starting motor? Assume the current is 300 A and the electrons travel through a copper wire with cross-sectional area 0.250 cm2 and length 0.900 m. The number of charge carriers per unit volume is 8.49 × 1028 m-3.

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RobertKer 6 months 2021-08-18T12:13:40+00:00 2 Answers 1 views 0

Answers ( )

  1. dangkhoa
    0
    2021-08-18T12:15:24+00:00
    Reply

    Answer:

    16.98 minutes

    Explanation:

    We are given that

    Current,I=300 A

    Area, A=0.250 square cm=0.250\times 10^{-4} m^2

    1 cm^2=10^{-4} m^2

    Length of wire,d=0.9 m

    Number of charge carriers per unit volume=n=8.49\times 10^{28} m^{-3}

    1 e=1.6\times 10^{-19} C

    We know that

    t=\frac{ne Ad}{I}

    Using the formula

    t=\frac{8.49\times 10^{28}\times 1.6\times 10^{-19}\times 0.25\times 10^{-4}\times 0.9}{300}

    t=1018.8 s=\frac{1018.8}{60}=16.98 minute

  2. vankhanh
    0
    2021-08-18T12:15:26+00:00
    Reply

    Answer:

    Explanation:

    current, i = 300 A

    Area of crossection, A = 0.250 cm² = 0.250 x 10^-4 m²

    length, l = 0.9 m

    number of electrons per unit volume, n = 8.49 x 10^28 /m³

    let v be the drift velocity and t be the time taken by the electrons

    i = n e A v

    300 = 8.49 x 10^28 x 1.6 x 10^-19 x 0.25 x 10^-4 x v

    v = 8.84 x 10^-4 m/s

    Time, t = distance / velocity

    t = 0.9 / (8.84 x 10^-4)

    t = 1018.8 s

    t = 17 minutes

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