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2 April, 22:52

You buy a 75-W lightbulb in Europe, where electricity is delivered at 240 V.

If you use the bulb in the United States at 120 V (assume its resistance does not change), how bright will it be relative to 75-W 120-V bulbs?

Assume that brightness is proportional to power consumption.

a. 2.5 X 10^-1

b. 1.0

c. 7.7 X 10^2

d. 19

e. 4.0

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  1. 2 April, 23:07
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    a. 2.5 X 10^-1

    Explanation:

    First of all we shall calculate the resistance of the bulb of 75W, 240 V.

    power = V² / R, V is potential and R is resistance

    75 = 240² / R

    R = 240² / 75

    = 768 ohm.

    Now this bulb is used with 120 V

    current = 120 / 768

    =.15625 A

    power = V X I

    potential x current

    = 120 x. 15625

    = 18.75 W.

    comparing it with 75 W

    the ratio

    18.75 / 75

    = 2.5 x 10⁻¹.
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