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A set of Christmas tree lights consists of 40 filament lamps connected in series across a supply of 240 V. Each lamp carries a current of 250 mA. Calculate the potential difference across a lamp.?
D4321
Since we don't know any different, we must assume that the little lamps are all
electrically identical.
Then, as long as the string is lighted and nothing has burned out yet, the current
through it doesn't matter. The supply voltage divides equally across each unit in
the string.
240/40 = 6 volts across each little lamp.
Since we're also given the current in the string, we can also go on to calculate:
-- Resistance of each lamp = E/I = 6/0.25 = 24 ohms
-- Power dissipated by each lamp = E I = 6 x 0.250 = 1.5 watts
-- Total power supplied by the source = 1.5 watts x 40 lamps = 60 watts
or 240 volts x 0.250 amps = 60 watts.
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∙ 12y ago
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