CK-12-Physics-Concepts - Intermediate

18.3. Energy Transfer in Electric Circuits http://www.ck12.org

Solution:

a.P=V I= ( 120 V)( 2. 0 A) = 240 W

b.E=(^2403 J./ 6 ×s)( 1086 h)(J/^3600 kW hs/h)= 1. 92 kW h

c. Cost= ( 1. 92 kW h)( 30 )($0. 15 ) =$8. 64

Summary

• Electric power is the energy per unit time converted by an electric circuit into another form of energy.


• The formula for electric power isP=I^2 R.


• The electric energy transferred to a resistor in a time period is equal to the electric power multiplied by time,
  E=Pt, and can also be calculated usingE=I^2 Rt.


• Electric companies measure their energy sales in a large number of joules called a kilowatt hour (kWh) which
  is equivalent to 3. 6 × 106 J.

Practice

Questions

The following video is on electrical energy and power. Use this resource to answer the questions that follow.

http://youtu.be/NWcYBvHOiWw

MEDIA

Click image to the left for use the URL below.

URL: http://www.ck12.org/flx/render/embeddedobject/65502

1. What is this video about?


2. What is the definition of electrical power?


3. What happens to the electrical energy that is not converted into work?

Instruction and practice problems related to the energy delivered by an electric circuit:

http://www.physicsclassroom.com/Class/circuits/u9l2d.cfm

Review

Questions

1. A 2-way light bulb for a 110. V lamp has filament that uses power at a rate of 50.0 W and another filament
   that uses power at a rate of 100. W. Find the resistance of these two filaments.


2. Find the power dissipation of a 1.5 A lamp operating on a 12 V battery.


3. A high voltage( 4. 0 × 105 V)power transmission line delivers electrical energy from a generating station to a
   substation at a rate of 1. 5 × 109 W. What is the current in the lines?


4. A toaster oven indicates that it operates at 1500 W on a 110 V circuit. What is the resistance of the oven?
   
   
   • electrical energy: Energy is the ability to do work, so electrical energy is the work done by an electrical
     circuit.