Electricity Study Guide

Static electricity is an imbalance of electric charges within or on the surface of a material. Unlike current electricity, which involves the flow of electrons, static electricity involves charges that remain stationary. The production of static electricity often occurs when two different insulating materials are rubbed together. This process, known as triboelectric charging, causes electrons to transfer from one material to the other. The material that gains electrons becomes negatively charged, while the material that loses electrons becomes positively charged. For example, rubbing a plastic rod with a cloth causes electrons to move from the cloth to the rod, making the rod negatively charged and the cloth positively charged.

Once objects are charged, they can exert forces on each other. These forces can be either attractive or repulsive. The fundamental rule of electrostatics states that like charges repel each other (e.g., two positive charges or two negative charges will push each other away), while opposite charges attract each other (e.g., a positive charge and a negative charge will pull towards each other). These forces act without the objects needing to be in direct contact, demonstrating action-at-a-distance. You can observe this by holding a charged comb near small pieces of paper; the comb will attract them. The greater the charge on the objects, and the closer they are, the stronger these electrostatic forces will be. A more dramatic effect of static electricity is sparking. If enough charge builds up on an object, and it is brought close to another object with a different charge or to an earthed object, the insulating air between them can break down. This breakdown allows electrons to rapidly jump across the gap, creating a visible spark and often a crackling sound, as seen with lightning or when touching a metal object after walking across a carpet.

A magnetic field is the region around a magnet where a magnetic force can be detected. This force acts on other magnets or magnetic materials like iron, nickel, and cobalt. The characteristics of a magnetic field include both strength and direction. The strength of a magnetic field is strongest at the poles of the magnet (the ends) and decreases as you move further away from the magnet. This means that a magnetic force will be strongest closest to the magnet and weakest furthest away. The direction of a magnetic field is conventionally defined as the direction a free-moving North pole of a compass would point. Outside a bar magnet, magnetic field lines emerge from the North pole and enter the South pole, forming continuous loops. Inside the magnet, the field lines go from the South pole to the North pole. The direction at any given point in the magnetic field can be shown by drawing field lines with arrows. Where the field lines are drawn closer together, the magnetic field is stronger. Where they are further apart, the field is weaker. These lines never cross each other. Magnetic fields are invisible, but their effects can be observed using compasses or by sprinkling iron filings around a magnet, which align themselves with the field lines.