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Dissecting Generators

Electric and Magnetic Fields

 We see evidence of fields changing when we place compasses near a moving magnet, or near a coil of wire attached to a generator. Fields help to explain how energy can transfer when objects are not touching. There are three kinds of fields in physics that transfer energy between objects: gravitational fields, electrical fields, and magnetic fields. Fields are invisible and help us understand the strength and direction of force another object moving into the field may experience.  Which fields do you think might be involved when energy transfers in an electric circuit?

Electric and magnetic fields are closely connected, especially in devices like generators, which produce electricity. To understand this relationship, let's start by defining electric fields and magnetic fields.

A magnetic field is an invisible force field that determines the strength and direction a magnetic object will be pushed or pulled.  An electric field is an invisible force field created around charged particles, like electrons that can push or pull on other charged particles. When a charged particle, like an electron, encounters an electric field, it will change the motion of the electron.  When a magnetic object, or another magnet, encounters a magnetic field, it will change its motion.

In class, we connected a coil of copper wire to a battery and made observations with compasses.  We found that when electrons move through a coil of wire, a magnetic field forms around the coil!  This allowed us to make the connection that when charged particles move, they generate a magnetic field.  This means that any time electric current flows through a wire (which is just a bunch of moving electrons), a magnetic field forms around the wire. The faster the particles move or the more current you have, the stronger the magnetic field.

Now, let's look at the opposite effect. When a magnetic field changes—like when a magnet moves near a wire—it can create an electric field. This electric field can push electrons in the wire, causing a flow of electric current. This is the basic idea behind how a generator works.  In a generator, magnets are moved around or near coils of wire. As the magnets move, their magnetic fields change. This changing magnetic field creates an electric field in the wire, causing electrons to move, which generates electricity. The faster or more powerfully the magnets move, the more electricity is produced. 

Energy Transfer in a Generator

Based on our models, how are matter changes related to energy transfer?  Is there a cause-effect relationship?

• Kinetic energy from the hand is transferred to the rod and magnets

• The kinetic energy changes into magnetic and electric energy as the moving magnets create an electric field

• The electric field pushes electrons in the coil and through to the wires as electric energy

• Electric energy is eventually released in the form of heat/light/sound energy depending on the device it is used by!