You buy a 75-W lightbulb in Europe,where electricity is deliveredto
home at 240 V. If you use the lightbulb in the United States at120
V (assume its resistance does not change). how bright will itbe
relative to 75-W 120-V Bulbs? [ Hint: assume roughly thatbrightness
is proportional to power consumed]
home at 240 V. If you use the lightbulb in the United States at120
V (assume its resistance does not change). how bright will itbe
relative to 75-W 120-V Bulbs? [ Hint: assume roughly thatbrightness
is proportional to power consumed]
please show work.
Answer
resistance of bulb is found by:
.
P = V2
/R 75
=2402
/R R
= 768 ohms
/R 75
=2402
/R R
= 768 ohms
.
Now find the power it uses when plugged into 120 V:
.
P = V2 / R = 1202 /
768 = 18.75 Watts
768 = 18.75 Watts
.
So compared to a 75 watt bulb is it is only:
.
18.75 /
75 = 1/4
as bright
75 = 1/4
as bright