Electricity Notes

Electricity Part A All matter is composed of atoms. Atoms are made up of smaller particles called protons, neutrons, and electrons. Protons are positively charged and electrons are negatively charged. According to the law of electric charges, like charges repel and opposite charges attract. If an atom loses electrons it becomes positively charged. If an atom gains electrons it becomes negatively charged.

There are three ways to “charge” an object... 1. Conduction– e- are transferred by direct contact Ex) uncharged metal & + charged glass rod (e- travel from metal to glass rod leaving the metal + charged) 2. Induction- when charges in an uncharged object are rearranged w/o direct contact Ex) – charged balloon and neutral wall (+ charged object near a neutral object and e- in neutral object are attracted to + charged object & move towards it) 3. Friction- when two objects are rubbed together electrons are “wiped” from one to another Ex) rub a plastic ruler with a cloth (e- are transferred from the cloth to the ruler)

Charge can be detected by using an Electroscope. Ex) Glass flask with a metal rod inserted through a rubber stopper. There are two metals leaves at the bottom of the rod. Leaves hang straight down when not charged and move apart when charged. Uncharged Charged

Static Electricity Static – not moving Static electricity is the build up of charges on an object. The charges that create static electricity do not move away from the object they are stuck to.

Why do clothes stick together after they are taken out of the dryer? When you dry clothes in the dryer, different fabrics rub together, and electrons from a cotton sock (for instance) may rub off onto a polyester shirt. That's why clothes sometimes stick together and make sparks when you pull them apart.

How does a fabric softener (dryer sheet) work to prevent static cling? As these sheets bounce around with your clothes, they add a uniform antistatic coating to the fabric. Rather than cotton rubbing against polyester, you've got the antistatic coating on the cotton rubbing against the antistatic coating on the polyester. No electrons rub off and you don't get any static cling.

The loss of static electricity is discharge. Gradually, over time, charges that build up on an object leave the object. Electric discharge may happen rapidly or slowly. The most dramatic example of electric discharge is lightning.

Current Electricity Electric current is a continuous flow of electrons. Current is how fast charge passes at a given point. There are 2 types of electric current: Alternating Current (AC) and Direct Current (DC). Electric current produced by batteries is DC and electric current from your home outlet is AC.

Current in a wire is determined by voltage and resistance Current in a wire is determined by voltage and resistance. The higher the voltage, the more energy is released. Resistance is the opposition to the flow of electric charge. It is represented with the symbol http://electronicsclub.info/circuitsymbols.htm The higher the resistance, the less current is in it. Resistance can change depending on an object’s material, thickness, length, and temperature.

An example of a material that has a low resistance is copper. Iron is a good conductor. Materials with a low resistance are used to make wires. A thick pipe has less resistance because there are more spaces for current to travel through. A thin pipe has more resistance because it does not have to move around many spaces.

In general, resistance increases as the temperature of a metal increases. This happens because atoms move faster at higher temperatures and get in the way of electric charge. If you cool certain materials, resistance will drop to zero. These materials are known as superconductors. They can be useful because very little energy is wasted when current travels through them.

Comparing Electricity & Magnetism + and – Charges North and South Poles Like Charges Repel Like Poles Repel Unlike Charges Attract Unlike Poles Attract electric field lines flow from + to - magnetic field lines flow N to S

In order to learn more about magnetism, electricity, and circuits, let’s make an Electrifoldable!