Power, voltage, and a damn brownout?

Question

Say the voltage of the house went from 120volts to 108 volts. What would be the power consumed by a 100 watt bulb (that is, a lightbulb that consumes 100watts when connected to 120volts).

Answer 1

it will consume the same as befor
watt = volt x amp.
100 watt = 108 volt x amp
100 watt = 120 volt x amp

the effect will be in amps. only

Answer 2

The lightbulb can be modeled as a resistor, I believe. 100watts means the power it will use at its specificed rating, 120V. At some voltage lower than that, it will use less power. 120^2V/100W = 144 ohms, which means at 108 V, it will use 81W. This is why it gets dimmer at lower voltages. If you turned the voltage down from 120 to 108, it will not stay at the same brightness. However, for motors and other devices, a reduction in voltage results in an increase in current; these devices are not ohmic.

A lightbulb isn't ohmic either (but can be linearly approximated as ohmic over some intervals), when it is cold the resistance is lower, which results in more current, which is why most light bulbs burn out when you turn them on. As the lightbulb heats up, the resistance increases, current decreases, and you have light.

Answer 3

a watt is equal to voltage times amps.
Thus a 100 watt light bulb connected to 120 volts requires .833 amps to operage. 100/120
if there was only 108 volts, it is 100/108. = .9259 amps to fully operate
At a certain point depending on the house fuses, the current will exceed the rated value and the circuit breaker will be thrown.

Power is the same thing as watts, a 100 watt bulb uses 100 watts to operate. the amps will change by the varied voltage.

Answer 4

Where:

W = V x I
&
R = V/I

Where:
W = 100W, V = 120V, I = 0.833A (100W/120V),
therefore bulb R = 120/0.833
R = 144.06 Ohms

if: 108V..then...W = V x I...= 108V x I (where I = V/R = 108V/144.06Ohms)

so...
W = 108V x 0.749A
W = 81W

therefore if the resistance remains the same and the voltage changes the current changes also and is directly proportional to the change in voltage in the circuit.

So:...same resistance, then less voltage = less current = less power output and use.