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The force that acts across the air gaps between magnets is the same force that creates wonders such as the Aurora Borealis. In fact, magnetic effects pervade our lives in myriad ways, from electric motors to medical imaging and computer memory. In this chapter, we introduce magnets and learn how they work and how magnetic fields and electric currents interact.

Forces at a distance are explained by fields (gravitational, electric, and magnetic) permeating space that can transfer energy through space. Magnets or electric currents cause magnetic fields; electric charges or changing magnetic fields cause electric fields.

Magnetism is an interaction that allows certain kinds of objects, which are called ‘magnetic’ objects, to exert forces on each other without physically touching. A magnetic object is surrounded by a magnetic ‘field’ that gets weaker as one moves further away from the object. A second object can feel a magnetic force from the first object because it feels the magnetic field of the first object. The further away the objects are the weaker the magnetic force will be.

• Predict how current will change when resistance of the circuit is fixed and voltage is varied.
• Predict how current will change when voltage of the circuit is fixed and resistance is varied.

Electrical devices convert the electrical energy carried by the charges into other types of energy such as heat, sound, and motion. Components in the appliance resist the flow of charge and are referred to as resistors. In this unit1 you will understand what resistance is, the factors that affect the resistance and the relationship between resistance and current.

Most of us use electricity every day in many different ways so it is important that we understand the dangers, or hazards, associated with electricity and we know how to use it safely.

When a circuit is connected and complete, charge can move through the circuit. Charge will not move unless there is a reason, a force to drive it around the circuit. Think of it as though charge is at rest and some- thing has to push it along. This means that work needs to be done to make charge move. A force acts on the charges, doing work, to make them move. The force is provided by the battery in the circuit.