Understanding Electricity: AC vs DC

• Electricity is a widely used form of energy for lighting, heating, powering devices etc.
• Electricity can be generated from fossil fuels, nuclear fuels, solar, wind, hydro, geothermal sources and more.
• Electricity is most often generated at a power plant by electromechanical generators, that are primarily driven by heat engines fueled by combustion or nuclear fission.
• The transmission process involves stepping up voltage for long-distance transfer then stepping down voltage before entering houses.
• The types of electricity are static electricity and dynamic electricity, which can be AC or DC.

Direct Current (DC)

• DC flows in one direction through a wire
• A battery is an example of DC

Alternating Current (AC)

• AC reverses the direction of the current flow in regular patterns.
• Plugging a toaster into a wall outlet is an example of AC
• Alternating current is an electric current that is constantly changing direction, produced by most generators and used in mains electricity.
• Motors often work using alternating current.
• The voltage of alternating current is easily changed with a transformer.
• Alternating current can be transferred efficiently over large distances.
• In most countries, the electricity supply is a.c. with a frequency of 50 Hz or 60 Hz.

Electromagnetic Induction

• Electromagnetic induction is the process where a wire moved near a magnet or a magnet moved near a wire causes an electric current to flow in the wire.
• These principles of electricity generation were discovered by Michael Faraday in 1831.
• Faraday's law of electromagnetic induction states: "Whenever a conductor is placed in a varying magnetic field, an electromotive force is induced."
• Electromagnetic induction is the technical name for the fact that, when a wire is moved near a magnet or a magnet is moved near a wire, an electric current flows in the wire.
• If the coil is part of a complete circuit, the induced e.m.f will make an induced current flow around the circuit.
• Generating electricity from motion is called electromagnetic induction.
• A coil of wire and a magnet moving relative to each other are needed to induce a voltage across the ends of a wire.
• This is called the dynamo effect.

Increasing the induced current

• Increase the speed at which the coil rotates.
• Increase the strength of the magnetic field.
• Increase the number of turns in the coil.
• Increase the total area of the coil.
• In a power station generator, an electromagnet is often used as this can provide a stronger magnetic field than is possible with a permanent magnet.

Fleming's Right-Hand Rule

• Fleming's right-hand (generator) rule shows the direction of induced current when a conductor attached to a circuit moves in a magnetic field.
• First finger points in the direction of the magnetic field.
• Thumb points in the direction of motion.
• Second finger points in the direction of (conventional) induced current.

Direction of Induced E.M.F

• An induced current always flows in a direction such that it opposes the change that produced it (Lenz's Law).

Electric Generators

• Can generate electricity by spinning a coil in a magnetic field.
• Converts mechanical energy to electrical energy.
• There are two types: AC generator and DC generator.
• The principle is electromagnetic induction.
• Supplies mains electricity to homes, offices, and factories from power stations
• Provides current to bicycle lights

AC Generator

• An AC generator converts mechanical energy into electrical energy in the form of alternative emf or alternating current
• AC generator works on the principle of electromagnetic induction
• The three main generator components are a field magnet, an armature, and slip rings with brushes.
• If the armature is rotating with a constant angular velocity in a constant magnetic field, the magnitude of the induced emf and current varies sinusoidally with respect to time.

Increasing Voltage in an AC Generator

• Turn the coil rapidly
• Use a coil with more turns of wire
• Use a coil with bigger area
• Use stronger magnets

Electric Motors vs Generators

• Electric motors convert electrical energy into mechanical energy and use electricity.
• Electric generators convert mechanical energy into electrical energy and generate electricity.
• Electric motors follows Fleming's left hand rule
• Electric generators follows Fleming's right hand rule
• Electric motors are based on the principle that "Current carrying conductor placed in magnetic field experiences force"
• Electric generators are based on the principle of Electromagnetic Induction

Exercise 21.1 from Workbook

• A wire is moved through the field of a magnet: Current induced
• A magnet is held close to a wire: No current induced
• A magnet is moved into a coil of wire: Current induced
• A magnet is moved out of a coil of wire: Current induced
• A magnet rests in a coil of wire: No current induced.
• To increase the strength of induced current: Increase magnetic field strength, use more turns of wire in the coil, turn the coil faster, use larger area of cross-section of the coil.
• When a magnet is moved towards a coil of wire, the direction of the induced current is reversed.
• Increasing the rate of change of the magnetic field through the coil, increasing the rate of cutting of field lines by the coil results to increased induced current.