Unit B Conclusion: Unit B Conclusion

1. Unit B Conclusion

Unit B Conclusion

In Module 3 you learned that all matter consists of two opposite types of charges (positive and negative), that these charges cannot be created or destroyed, and that like charges repel and opposite charges attract. You also investigated how electrically charging objects by friction, conduction, or induction creates an imbalance of charge by causing gain or loss of electrons. These concepts helped you to explain the behaviour of electrical charges.

You then explored electric forces and fields. You learned why “action at a distance” forces such as gravity and some electrical forces occur because of the presence of electric fields. An electric field is the electric force acting on a positive test charge (q) at a point in space. It can be expressed as the following equation:

You then compared gravitational and electrical fields and discovered that they are very similar in the way they act as they both vary in strength according to the inverse square law. You discovered a key difference between them was that an electrical field could be in one of two directions, depending on the charge, while a gravitational field only has one direction—toward the mass.

From this you went on to Coulomb’s law, which states the electric force between two charged objects is directly proportional to the product of the charges and inversely proportional to the square to the distance between them.

This knowledge of electric field theory helped solve the mystery of “unnatural” and “unusual” phenomena, such as St. Elmo’s fire and Corona Discharge on power lines and other conducting objects such as airplane wings.

You learned two more similarities between electrical fields and gravitational fields. First, a charged object in an electrical field can store potential energy similar to that of a mass in a gravitational field. Second, a mass travelling in a uniform gravitational field is similar to that of a charge travelling in an electric field. They are both in motion with constant acceleration and the field causing the force diminishes according to the inverse square law.

Lastly, you investigated the difference between electrical potential (or voltage) and electrical potential difference, (ΔV). These concepts were reinforced in Module 4 where you explored how electricity and magnetism are related.

In Module 4 youwere introduced to magnetic fields and how to draw these fields surrounding a bar magnet. You learned that the magnetic field surrounding a bar magnet is from north to south and when a compass is placed in a magnetic field, the north pole of the compass needle points in the same direction as the field.

As magnetic fields became clearer you learned that the connection between moving charge and the production of magnetic fields is the first step in understanding electromagnetism observed in nature and used in modern technologies, such as electrical generators and motors.

Next, you applied your knowledge of magnetic fields to explore magnetic forces. You discovered that when a charged particle moves in an external magnetic field, it exhibits uniform circular motion. The inward force is a magnetic force that is proportional to the product of the particle’s speed (perpendicular to the magnetic field) and charge and the strength of the magnetic field in which it moves. Expressed mathematically it is

From here you started exploring the connection between electricity and magnetism. You learned that a magnetic force is generated when a current-carrying conductor is located in a perpendicular magnetic field, which is similar to that of a moving charge.

You also discovered why the direct current electric motor is essentially an electric generator in reverse. When a conductor is forced through a perpendicular magnetic field, a current is induced in the wire. This is known as the generator effect. Furthermore, the direction of the induced current is such that it produces a magnetic field that opposes the motion that is causing it. This is known as Lenz’s law.

Lastly, you explored how the motor effect and the generator effect are linked by the interaction of electric and magnetic fields.

Throughout Unit B you explored the properties of electric and magnetic fields in various contexts. A very important context is how we use the interaction of electric and magnetic fields to generate and distribute electricity and to power numerous devices. It is this complex interaction between electricity and magnetism that has revolutionized our modern way of life.