bulb question.

[matt01165]

What happens when you use a 230v bulb  in a 110v outlet? even though they are both 100 watts?

[Pete]

Where light bulbs are concerned, Sylvia is right......here's the science.....

 

If you tried to use something that was designed for 240 Volts on only 120 Volts, the result is not that you would get half the power output: you would get only a quarter!

That is because of Ohms Law, which says:

Amps = Volts divided by Resistance (Ohms)

and the Power Law which says:Power (Watts) = Volts multiplied by Amps


so it is also true to say:

Power = Volts x ( Volts / Ohms ) or V²/Ohms

If the appliance was designed to run on 240 Volts, with a certain number of Ohms of resistance, its Power is given by the formula as:


Power = 240 x 240 / Ohms = 57600 / Ohms.

So, if the Resistance of the appliance is 5 Ohms its power consumption is 57600 / 5

= 11,520 Watts = 11.52 KiloWatts

If we tried to use that same appliance on 120 Volts, which is half of 240 volts:

The appliance's resistance would stay the same so the resulting power taken at

120 volts is:

= 120 x 120 / Ohms = 14400 / 5 = 2880 Watts

Another way to see it is: if V = 240 volts, and if you are plugging into only half of V:

Power = (V/2)² / Ohms = (V²/4) / Ohms

but as the appliance's resistance would still be the same, the resulting power =

1/4 x (240 x 240 / Ohms) = 1/4 x 57600 / 5 = 2880 Watts.

Anyway, however you calculate it, 2880 Watts at 120 volts is only a quarter of the power which would be supplied at 240 Volts, 11520 Watts.

The story does not end here, however!

If you want to supply 11,520 Watts of power at only 120 volts, the current required would be 11520 / 120 = 96 Amps.

To allow such a current to be carried safely to the appliance without catching on fire would require extremely thick wiring to be used from the main breaker panel to the appliance. Also, it would not be possible to use any standard 120 Volt breakers, plugs and socket outlets to carry such a current.

So no appliances for normal domestic home use are manufactured to operate at such high power outputs on 120 Volts.

However, to supply a power of 11,520 Watts at 240 volts, the current required would be 11520 / 240 = 48 Amps. This is well within the normal specifications for the standard wiring sizes and outlets used for 240 Volts supplies, to allow such a current to be carried safely to the appliance without catching on fire.

That is why high-powered appliances, such as clothes dryers and kitchen ranges, for normal domestic home use, are manufactured to operate at 240 Volts.