Fundamental Principles of Electricity and Circuit Components

Methods of Charging

• Charging by friction: Involves one material losing electrons and the other gaining. This usually occurs when you rub two objects together and is determined by the triboelectric series.
• Charging by induction: The process where a charged particle is held near an uncharged particle.

Kirchhoff's Laws

1st Law: The current in equals the current out.

2nd Law: EMF equals the Potential Difference (P.D.) on a loop.

Electric Shock Severity

Factors that affect the severity of a shock:

• The amount of current (A) involved in the electric circuit
• Duration and time of exposure

Material Conductivity

Conductors: Allow electrons to pass readily through them (e.g., copper wire).

Insulators: Restrict the movement of charge (e.g., plastic sheath).

Semi-conductors: Materials that have a conductivity value between a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite manner.

Electric Fields and Resistance

Arrows on a diagram represent the force a positively charged particle would experience. 8arro \

Current is what kills, not voltage.

Factors Affecting Resistance

• Type of material
• Length of material: Increases resistance
• Thickness: Decreases resistance
• Temperature of conductor: Increases resistance

For a graph: An Ohmic resistor is represented by a straight line, as current (i) and voltage (v) remain constant.

Direct and Alternating Current

Direct Current (D.C.): An electric current that always flows in one direction (e.g., cells, batteries, and electric circuits). It cannot be transferred over long distances.

Alternating Current (A.C.): An electric current that is constantly changing direction (e.g., generators and mains in our homes). It can be transferred efficiently over large distances with transformers.

Magnetic Flux and Induction

Magnetic Flux: The strength or density of the magnetic field.

Increasing Potential Difference Flux

P.D. flux increases when you:

• Increase the speed of the movement
• Increase the strength of the magnetic field
• Increase the number of turns on the coil
• Increase the area of the coil

For coil questions, if there is a higher or lower output or turn on coils, it refers to a step-up or step-down transformer.

Circuit Safety Devices

• Fuses: A length of wire designed to melt when the current rises above the circuit level.
• Circuit Breakers: An electromagnetic device that breaks the circuit after the current becomes too high.
• Residual Current Devices (RCD): Detects live current and shuts off the power.
• Double Insulation: An additional safety layer for electrical appliances.
• Earth Wire: Connected to the metal casing of a device (like a dryer); if any current is present, the earth wire will ground it, making the device safe to touch.

Diodes and Sensors

Forward Diodes: These are 'on' and allow current to run through after reaching the threshold voltage.

Reverse Diodes: These are in 'off' mode when the voltage is less than the threshold but greater than the breakdown voltage.

Zener Diode: Specifically made to operate under reverse diode conditions.

Light Dependent Resistor (LDR): As the light level increases, the resistance decreases (e.g., used in car headlights).