1. UEENEEE003B Solve Problems in Single Path DC Circuits Energy, Work and Torque

2. Refers to an activity involving a force and movement in the direction of the force. A force of 20 newtons pushing an object 5 meters in the direction of the force does 100 joules of work. 8/9/2011 Revision02 2 Work

3. Is the rate of doing work or the rate of using energy, which are numerically the same. If you do 100 joules of work in one second (using 100 joules of energy), the power is 100 watts. 8/9/2011 Revision02 3 Power

4. Is the capacity for doing work You must have energy to accomplish work – it is like the ‘currency’ for performing work. To do 100 joules of, you must expend 100 joules of energy. 8/9/2011 Revision02 4 Energy

5. Energy cannot be created or destroyed but can be converted from one form to another. When energy is converted, work is done. To produce electrical energy one of the following forms of energy must be converted: 1. mechanical energy (friction, pressure); 2. chemical energy (chemical action); 3. magnetic energy (magnetism); 4. heat energy (heat); 5. light energy (light). Revision02 5 Energy

6. Work Work is done when a body is moved through a distance by a force acting on it. Power The rate of doing work Energy The potential to do work 8/9/2011 Revision02 6 Work, power and energy

7. Torque Torque is the turning effort a motor uses to turn something. This motor develops torque to turn the gears. Revision02 7

8. Revision02 8 Measurement of torque

9. Revision02 9 Torque Power= 2 x π x N x T / 60 If T = torque N = RPM How do we find the Torque ?

10. Kilowatt Kilowatt- hour meter to measure electrical energy. Kilowatt hours is a convenient unit rather than watt-seconds Revision02 10

11. 8/9/2011 Revision02 11 Efficiency of a Machine

13. The Input power is electrical. This is calculated using Voltage, and Current.

14. Power = Current x Voltage (watts)

15. P = IV8/9/2011 Revision02 12

16. 8/9/2011 Revision02 13 Watts loss area

17. Revision02 14 Efficiency Output  = ------------ x 100 Input Always as a percentage

18. An electric drive motor takes 48kW from the supply and delivers 42kW out of a gearbox into the load. What is the efficiency of the machine ? If a similar machine took 56kW from the supply and delivered energy to the load at 85% , what is the output of the unit ? Revision02 15 Student exercise

19. Whenever electric current flows, heat is generated. Nearly all electric circuits produce some heat. This heat is “lost” power. P = I² x R We will look at this later. Revision02 16 Losses are an indication of efficiency