Question

How do you calculate power dissipation in resistors and power delivered by voltage/current sources?

Answer 1

To calculate power dissipation in resistors and power delivered by voltage/current sources, you need to understand the relationships between voltage, current, and resistance.

Power Dissipation in Resistors:
The power dissipated in a resistor can be calculated using Ohm's Law and the power formula.

Ohm's Law states that:


=

×

V=I×R

where:


V is the voltage across the resistor,


I is the current passing through the resistor, and


R is the resistance of the resistor.

The power formula is:


=

×

P=V×I

where:


P is the power dissipation in the resistor.

Now, we can substitute Ohm's Law into the power formula to get the power dissipation in the resistor:


=
(

×

)
×

=

2
×

P=(I×R)×I=I
2
×R

Alternatively, you can also use:


=

2

P=
R
V
2
    ​


Power Delivered by Voltage/Current Sources:
The power delivered by voltage or current sources can be calculated by multiplying the voltage (V) across the source by the current (I) passing through it.

For a voltage source:


delivered
=

×

P
delivered
    ​

=V×I

For a current source:


delivered
=

×

P
delivered
    ​

=V×I

In both cases, the power delivered is positive, indicating that energy is being supplied to the circuit.

Keep in mind that power is measured in watts (W) and that it can be either positive (energy supplied) or negative (energy absorbed or dissipated). Negative power indicates that the source is absorbing power rather than delivering it. This can happen, for example, when a circuit has components like batteries or power supplies that are charging or being recharged.

Remember to use the correct units for voltage (V) and current (A) when performing these calculations. Also, be aware of the sign conventions for power, especially when dealing with sources that absorb power.