can anyone tell dis plzzzz!?!?!..i've my exam!!!?

Question

heya everyone..
in class 10 syllabus..physics...we got Electricity chapter...

in that one...we have two-three formulas of power..

power = I*I*R
and POWER = V*V / R

so my quesion is...in one case..power is directly proportional to R(resistance) and in second...itz inversely proportional to R...

howz it possible???...plzzz answer asap!!!

Answer 1

The two are really the same formula, and are related by ohm's law, V= I*R. You use the formula based on the information you have. If you know the current, use W= I^2*R; if you know the voltage, use W = V^2/R.

In the case of W = I^2*R, if you increase R, the W increases, but so does V, since V=I*R. In the case of W = V^2/R, if you increase R the current decreases (ohm's law I = V/R), and less current means less power.

The basic formula is W = I*V, and in order to know which way W goes, you have to take into account changes in both V and I, and changing R affects both.

Answer 2

power = I^2R

In this case, if you increase the resistance, then it takes more power to keep the current the same. The power source has to work harder to push the electrons through the higher resistance. If your decrease the resistance, then it take less power to keep the current the same. Make sense?

power = V^2/R

In this case, if you increase the resistance, it takes less power to maintain the voltage. For example, consider an open circuit between two battery terminals. The battery expends no energy to maintain the voltage. If you decrease the resistance, it takes more power to maintain the voltage. A battery doesn't last long with a short circuit across its terminals because it is expending as much energy as possible to maintain the voltage.

Answer 3

Nikita, first you must distinguish that
(1) P=iV applies to electric energy "TRANSFERS" of all kinds.
(2) P= (i*i)*R and P= (v*v)/R apply "ONLY" to the transfer of "ELECTRIC POTENTIAL ENERGY to Theral Energy" in a device with resistance. Thus, resistance is the key plyer in these EQs. and you may use either of the formulas in (2) dependent of you been given {i & R} or {V & R} to work with. Plug in i=2 V=4 R=2 to the EQs.