Chapter 7 Electricity

Section 1 Electricity

Structure of Atoms Atoms contain the following… ParticleChargeLocation Proton+1Nucleus Neutron0Nucleus Electron Outside the nucleus

Positive and Negative Charges In most atoms, the negative charge cancels out the positive charge. These atoms are said to be electrically neutral.

Static Electricity The accumulation of excess electrical charge on an object. The accumulation of excess electrical charge on an object.Ex: Walking on carpet. Electrons are transferred from the carpet to your shoes. Walking on carpet. Electrons are transferred from the carpet to your shoes. Lightning is a very large static charge Lightning is a very large static charge

Charges Exert Forces The force on the atoms depends on… 1. The distance between the atoms. 2. The amount of charge on the atoms. Opposite charges attract Like charges repel

An electric field surrounds every electric charge and exerts the force that causes other electric charges to be attracted or repelled. Any charge that is placed in an electric field will be pushed or pulled by the field. Electric Fields

Earth’s Electric Field

Law of Conservation of Charge A charge can be transferred from object to object, but cannot be created or destroyed. A charge can be transferred from object to object, but cannot be created or destroyed.

Static Charge

Charging Objects By Contact Charges can be transferred by rubbing or touching objects. Charges can be transferred by rubbing or touching objects. Ex: Rubbing your shoes on carpet or rubbing your hair with a balloon.

Charging By Induction (Charging at a distance) Charged objects brought near a neutral object will cause electrons to rearrange their positions on the neutral object.

Charging at a Distance The balloon on the left is electrically neutral. The balloon on the left is electrically neutral. The balloon on the right is negatively charged and produces a positively charged area on the sleeve by repelling electrons. The balloon on the right is negatively charged and produces a positively charged area on the sleeve by repelling electrons.

Lightning is a large static discharge. Lightning A static discharge is a transfer of charge between two objects because of a buildup of static electricity.

Eventually, enough charge builds up to cause a static discharge between the cloud and the ground. Lightning As the electric charges move through the air, they collide with atoms and molecules. These collisions cause the atoms and molecules in air to emit light.

Thunder Lightning also generates powerful sound waves. The electrical energy in a lightning bolt rips electrons off atoms in the atmosphere and produces great amounts of heat. The heat causes air in the bolt's path to expand rapidly, producing sound waves that you hear as thunder.

Grounding Connecting an object to Earth. Connecting an object to Earth. Providing a path for a charge to reach the Earth prevents an excess charge from building up. Providing a path for a charge to reach the Earth prevents an excess charge from building up.

Electroscope A device used to detect an electric charge. A device used to detect an electric charge.

Section 2 Electric Current

Electric Current The net movement of electrons in a single direction. The net movement of electrons in a single direction. Flows from higher voltage to lower voltage. Flows from higher voltage to lower voltage. Measured in Amperes. (amps) Measured in Amperes. (amps)

Voltage Difference The differences in electrical charges. The differences in electrical charges. Measured in Volts. Measured in Volts.

Circuits A closed path that the electric current follows. A battery can provide the voltage difference needed to keep current flowing.

Resistance Resistance is the tendency for a material to oppose the flow of electrons, changing electrical energy into thermal energy Resistance is the tendency for a material to oppose the flow of electrons, changing electrical energy into thermal energy and light. Resistance is measured in ohms Resistance is measured in ohms

Ohm’s Law Current (in amps) = voltage difference (in volts) Current (in amps) = voltage difference (in volts) resistance (in ohms) resistance (in ohms) I = V R

Section 3 Electrical Energy

Circuits There are 2 types of circuits: Series and Parallel

Series Circuit Have only one loop to flow through. Have only one loop to flow through. EX: flashlights, some holiday lights.

Parallel Circuits Contain two or more branches for the current to move through. Contain two or more branches for the current to move through. The current can flow through both or either of the branches. The current can flow through both or either of the branches. Advantage: When one branch opens the current continues to flow through the other branches. Advantage: When one branch opens the current continues to flow through the other branches.

Household Circuits A combination of parallel circuits connected in a network. A combination of parallel circuits connected in a network.

Protection From Overheating Fuses: Contain a small piece of metal that melts when it becomes overheated, breaking the circuit and stopping flow of current.

Circuit Breaker A circuit breaker contains a piece of metal that bends when the current in it is so large that it gets hot.