220V,100W燈泡,若接於110V電源時,其電功率多少?

First of all, you have to remember the basic Ohm’s Law and the corresponding equations (as follows), then you can find out Voltage (V)( 電壓), Current (I)( 電流), Resistance ( R) (電阻), Power(功率)(Watt):

V = IR - Ohm's Law ;
P = V * I - power dissipated in a resistor;
P = I^2 * R - power dissipated in a resistor in terms of the current ;
Q / t = I^2 * R
Q = I^2 * R * t
Q = (V^2 /R) * t

http://en.wikipedia.org/wiki/Joule%27s_law


P = V^2 / R


http://en.wikipedia.org/wiki/Ohm

To calculate (ohm)(歐姆) if (voltage)(電壓)(V) and Output (Watt) (瓦特) are given, and/or to calculate Output (Watt) (瓦特) if (voltage)(電壓)(V) and (ohm)(歐姆) are given, use:

P = V^2 / R

Thus,

100 = (220)^2 / R

R = (220)^2 / 100 = 484 ohms

If the voltage is changed to 110 and the ohms not changed, then

P = (110)^2 / 484

P = 25 (watts)


希望可以幫到你.