Unsa ang Elektrisidad?

Boltay ug kuryente mao ang duha ka pangunahon nga parametro sa usa ka elektrisidad nga sirkuito. Apan, ang tulo ra nga boltay ug kuryente wala masufficient aron ipakita ang pagkatao sa usa ka elemento sa elektrisidad nga sirkuito. Kiniyahan nato nga mag-ila kung unsaon ang panghihigayon sa elektrisidad, ang elemento sa sirkuito makapahandle. Tanan natong nakita nga ang 60 watts nga elektrisidad nga lampara naghatag og gamay nga ilumination kay sa 100 watts nga elektrisidad nga lampara. Sa panahon natong bayad sa elektrisidad, ang among bayad mao ang bayad sa panghihigayon sa elektrisidad sa isip nga panahon. Busa, ang panghihigayon sa elektrisidad calculation mahalaga sa pag-analisa sa usa ka elektrisidad nga sirkuito o network.

Suppose, an element supplies or consumes an energy of dw joules for a time of dt second, then power of the element can be represented as,

This equation can also be rewritten as,

Hence, from the as the expression of voltage and current in the equation are instantaneous, the power is also instantaneous. The expressed power is time-varying.

So, the power of a circuit element is the product of voltage across the element and current through it.

As we have already told that a circuit element can either absorb or deliver power. We represent the absorption of power by putting a positive sign (+) in the expression of power. Likewise, we put a negative sign (-) when we represent the power delivered by the circuit element.

Passive Sign Convention

There is a simple relationship between the direction of current, polarity of voltage and sign of the power of a circuit element. We call this simple relationship as passive sign convention. When a current enters in an element through its terminal of positive voltage polarity, we put a positive sign (+) before the product of the voltage and current. This implies that the element absorbs or consumes power from the electric circuit. On the other hand, when the current through the element leaves its terminal of positive voltage polarity, we put a negative sign (-) before the product of the voltage and current. This implies that the element delivers or supplies power to the electric circuit.

Let us take a resistor connected across two circuit terminals. Although, the rest of the circuit is not shown here in the figure. The polarity of the voltage drop across the resistor and the direction of current through the resistor are shown in the figure below. The resistor is consuming a power of vi watts as current i ampere enters in the resistor though its positive side of the dropped voltage v volt, as shown.

Let us take a battery connected across two circuit terminals. Although, the rest of the circuit is not shown here in the figure. The polarity of the voltage drop across the battery and the direction of current through the battery are shown in the figure below. The battery is delivering a power of vi watts as current i ampere enters in the battery of v volt through its positive polarity terminal as shown.

Source: Electrical4u

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