Unit D Lesson 12: Motors

 Learning Targets

Big Question: What puts the 'move' in motors?
We have motors in an amazing variety of places, and the move away from fossil fuels is making efficient electric motors more important than ever.

At the end of this inquiry, you should be able to answer the following questions:

  • What are the functions of the main parts of an electric motor?
  • What is the difference between a motor and a generator?
  • What is the difference between alternating current and direct current?

Pages 325 and 331 in your textbook will help you answer these questions.


Watch

As you watch the video "Super Simple Electric Motor", think about what makes the motor move. Do you wonder how electric motors work? Where does the electricity come from? How is the electrical energy converted to mechanical motion? What parts are needed to make a motor work? Read on to find out how we use electricity to operate many things in our world.


 Try It!

Practice Worksheet: Motors

  1. DOWNLOAD this practice worksheet (S9_UD_S3_L12_motors). If you prefer to use a Google Drive or PDF version of the worksheet, click here.

  2. Answer the questions on the worksheet as you work through the readings and videos in this lesson.

  3.  When you are satisfied with your responses you can check your work by clicking on the "SUGGESTED ANSWERS" button below.

    Wait! Don't view the suggested answers first. This practice work is not for marks, it is meant to help you check your understanding. Check the answers AFTER doing the questions! Keep the practice worksheet for study purposes. If you don't understand something, contact your teacher!

Figure 1 – Advances in batteries and electric motors are making electric cars more popular.


  1. a. Source of electricity
    b. Brushes
    c. Commutator
    d. Electromagnet
    e. Permanent magnets

  2. A motor uses electrical energy and converts it to mechanical energy.

  3. a. Permanent magnets
    b. Commutator
    c. Brushes
    d. Armature
    e. Power input/output

  4. AC is alternating current. It is current that switching back and forth producing a consistent frequency of energy. DC is direct current where the current comes out one end and loops around back to the beginning again.

  5. Transformers use electromagnetic induction so step-up or step-down the voltage. They are useful to provide extra voltage from the power station to your home to account for any voltage loss on the journey and to step-down the voltage so it an go into your home at a safe amount.
Electric Motors

Motors are used in almost every electrical device on the planet. Motors use electrical energy that is transformed into mechanical energy, which the is opposite of a generator. Often, we use the St. Louis motor to demonstrate the parts of any electric motor.

The St. Louis motor shows all the parts in the open so it allows you to understand how electrical energy is converted into mechanical energy.

Figure 2 – An electric motor is basically an electromagnetic coil is a permanent magnetic field. In this diagram, the coil is blue, located between the red and green magnets. When electric current flows through the coil, it becomes an electromagnet, which is then pushed to rotate by the force of interaction with the permanent magnetic field.

How a St. Louis Motor Works

  1. Current travels from the battery to the terminal, then through the conductive brushes, and then into the split ring commutator.
  2. From the split ring commutator, the current travels into the electromagnet (also called the armature).  This current causes a magnetic field, and the electromagnetic attains a North Pole or South Pole depending on current direction.
  3. When the armature becomes a North Pole on one side, it is attracted to the South Pole of the permanent magnet.  This causes the armature to rotate.
  4. This rotation continues because, as the split ring commutator turns, the other side of the armature is now connected to the other brush, making that side South Pole although it was once North Pole.  This action keeps repeating and, therefore, mechanical energy continues to be produced and the electromagnet continues to move.

Figure 3 – A St. Louis Motor is excellent for seeing how a motor works, but other than education, it has little practical purpose.


Watch

Understanding the basic parts of a motor will help you understand how electrical energy can be converted to mechanical energy.  When you watch the video "St. Louis Motor", give careful attention to the split ring commutator.  This piece of the motor allows the current to change to keep the electromagnet spinning.

Still having trouble understanding why an electric motor turns? Watch the following video "DC Motor Principle", it slowly and carefully explains why an electric motor spins.

There is a key difference between generators and motors. Generators use mechanical energy to produce electrical energy, but motors use electrical energy to produce mechanical energy. Physically they are very similar, but functionally they are opposites. A generator transforms mechanical energy into electrical energy. A motor transforms electrical energy into mechanical energy.

While you watch the video "Magnetism: Motors and Generators", look for the main difference between a motor and a generator.

Do you want to see how the world's simplest motor is made? Join Steve Spangler to learn how to make your own personal motor by watching the video "World's Simplest Motor - Cool Science Experiment".

Alternating Current and Direct Current

Electrical current is of two types. Direct current (DC) is current that goes in one direction, loops around the circuit, and then comes back to the beginning. This type of current is seen in the St. Louis Motor and in small devices such as a flashlight. Batteries supply DC current to circuits.

The other type of current is alternating current (AC), which changes back and forth constantly. It AC current coming into your home, supplied by power plants that may be many kilometres away. With current moving back and forth in the wires, you might think you would see the lights in your home blinking on and off. However, the current cycles so quickly (about 60 times per second) that it cannot be noticed.

Figure 4 – High voltage transmission lines carry AC current.

 Watch


What do AC and DC currents look like in circuits?  Watch "AC vs. DC Power".

 
 
Watch "What do AC and DC mean for Electronics?"

 
 
There is a very interesting story regarding the choice between AC and DC current. Watch "AC vs DC with Nikola Tesla and Thomas Edison"

Transformers

Sometimes, the voltage must be increased or decreased.  Transformers can do that.  Electricity is produced at the power generation station and transmitted to your house.

Because voltage is lost along the way, power companies use step-up transformers to increase the voltage to accommodate any losses on the way.  The voltage is increased to 500 000 Volts for the journey to your house.  Transformers use alternating current (AC) in one coil to produce a current in the other coil.  As long as the two coils have a different number of wraps around an iron core, there will be a voltage change with minimal loss.

Power companies can step-down the voltage when needed.  When the current arrives at your farmyard or at your part of the town or city, a step-down transformer reduces the voltage to 240/120 Volts so it can be used safely in your home.



Interactive


Electromagnets
 
  1. This BrainPOP video reviews the concept of Electromagnets. Click here to watch "Electromagnets".

    You will need a username and password to access the video.
    • Username: 0099
    • Password: students

  2. Click here to complete the quiz on Electromagnets.  Remember to check your answers at the end!