POWER

Instantaneous POWER

- absorbed by an element is the product of the 

instantaneous VOLTAGE across the element and 

the instantaneous CURRENT through it.

- is the power at any instant time.

Average POWER

- is the average of the instantaneous power 

over one period

Consider this is a circuit:

Find the average POWER supplied by the source and 

the average power absorbed by resistor.

To solve for the given circuit:

• Analyze the problem.
• First, get the current in the circuit.
• Use Ohm's Law or KVL. 
• Using Ohm's Law :  i = (5/_ 30) / (4 -j2)
• Answer : i = 1.118 /_ 56.57

•  No need to get the current in the resistor, because according to theory when it is in series the current is THE SAME.
• Then, Get the voltage on that resistor. 
• Use Voltage division or Ohm's Law. For Ohm's Law, substitute the value you've got in i.
• Using Ohm's Law AGAIN: V = 4i 
• Substitute the value you've got in i. 
• V = 4.472 /_ 56.57

•  Then, use the formula of the average power to get the absorbed average power.
• Equation :
• P = (1/2)(4.472)(1.118) 
• P = 2.5 W

• Then, the average POWER supplied by the voltage source is:
• Equation:
• P = (1/2)(5)(1.118) cos(30 - 56.57)
• P = 2.5 W