Q&A

# Why is it is always power consumption or power delivered more in usage?

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In circuit analysis why always the power has upper hand over energy? Even if we consider a simple battery circuit with a bunch of resisitors we always use the terms power delivered,absorbed,consumption etc. more compared to energy eventhough time is not under consideration( Power = Energy/time).Is it simply because power = voltage *current?

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In circuit analysis why always the power has upper hand over energy?

One obvious reason: -

If we calculate how much power a resistor dissipates we can calculate how hot it will get (knowing it's thermal resistance and ambient temperature and some other factors). We need to know how hot stuff gets because we need to ensure things don't get too hot and burn out.

Energy doesn't really help in this situation unless we know the timeframe in which the energy was used but, then we are talking about power.

However, there are many cases where we are more interested in energy (such as reactive components) so, there is no "upper hand"; just examples that require energy to be assessed and, examples that need power to be assessed.

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No. You use the right concept whenever you need to use it. There is no preference of "power" over "energy".

For example, the energy stored by a cap is equal to ${1\over 2} C V^2$. This is often used in computations.

It's also the energy you have wasted that you have to pay to your electricity provider.

On the other hand, power is useful to know how much heat is dissipated by resistors and like; this is why it is very often needed in electrical engineering.

ADDED: Perhaps most importantly, it is pointless to say "this circuit uses such quantity of energy during such amount of time": you just don't want to involve time into the expression of the circuit energy consumption. The time is an arbitrary choice of the user. It is much more pertinent to provide the power dissipated by the circuit, in order for the user to be able to obtain the energy by multiplying by the working time if he wishes.

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Power makes sense for steady state conditions. A certain energy will be used over one second. Then the same energy will be used the next second. And the next second. If I told you that such a circuit used 3 J, the first thing you'd ask is "When?", "Over what time?". Only knowing that is used 3 J at some time if it's doing the same thing over and over again is rather useless.

What matters in that case is the energy used per time. That comes up so often that we have a special name for it: "Power".

In some cases energy usage is "one off", and then it does make sense to talk about energy instead of power. For example, charging a capacitor to a particular voltage takes a fixed amount of energy, regardless of how fast or slow that energy is delivered. The same is true for how much energy an inductor can store before it saturates.

Power and energy are different metrics, so they have their different uses. We use whichever fits best to describe whatever phenomenon we are talking about.

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