Electricity & Magnetism

Electricity Electric charges are from protons+ which are positive particles and electrons- which are negative particles. Static Electricity – accumulation of excess electric charges on an object. Atoms become charged by gaining or losing electrons.

Law of Conservation of charge- electric charges can be transmitted from object to object, but it cannot be created or destroyed. Positive and negative charges exert forces on each other.

Conductors vs. Insulators Conductors– materials in which electrons move easily. Ex. Metals Insulators - materials in which electrons are not able to move easily. Ex. Wood, plastic, rubber Charging Objects Charging by contact – process of transferring charge by touching or rubbing. Charging by induction - rearrangement of electrons on a neutral object caused by nearby charged objects.

ELECTRIC CURRENT & CIRCUITS

Electric Current Electric current - net movement of electric charges in a single direction through a wire or conductor. Voltage difference - force that causes electric charges to flow; charges flow from high voltage to low voltage. Circuit - a closed path that electric current follows. Battery, wires and voltage difference allows current to flow.

Batteries Dry- cell - chemical reactions occur in a moist paste causing transfer of electrons. Ex. See battery above Wet-cell - contains two connected plates made of different metals in conducting solid. Ex. Car battery Resistance_- tendency for a material to oppose the flow of electrons, changing electrical energy into thermal and light energy. Making wires thinner, longer or hotter increases resistance. All materials have some electrical resistance measured in Ohms. Ω Ohm’s Law - current in a circuit equals voltage difference divided by resistance.

Electrical Circuits Circuit Symbols

Complex Circuit A circuit composed of both series and parallel circuits. Electrical energy enters your home at the Circuit breaker or fuse box and branches out to appliances, wall sockets and lights. Circuit Breaker - small piece of metal that bends when it gets hot, opening circuit and stopping current flow. Electric fuse - small piece of metal that melts if current becomes too high, opening circuit.

MAGNETISM AND ELECTRICITY

Magnetism Magnetism - refers to the properties and interactions of magnets in which there is a force of attraction or repulsion between like or unlike poles. Strength of force between two magnets depends on the distance between them. Magnetic field - exerts a force on other magnets and objects made of magnetic materials. (strongest closest to magnet)

All magnets have a north pole and a south pole. Like poles repel; unlike poles attract. Magnetic Materials Only a few metals, such as iron, cobalt & nickel are attracted to magnets or can be made into permanent magnets. Magnetic domains – group of atoms with aligned magnetic poles (too small to be seen with the eye) Permanent magnets are made by placing a magnetic material in a strong magnetic field, forcing magnetic domains to line up.

Magnetism and Electricity When an electric current flows through a wire, a magnetic field forms around the wire. Electron flow Strength of magnetic field depends on the amount of current flowing in the wire. Electromagnets - a temporary magnet made by wrapping a wire coil carrying a current around an iron core.

Electric motor - a device that changes electrical energy into mechanical energy. In a simple electric motor, an electromagnet rotates between the poles of a permanent magnet. Increase strength of the magnetic field by adding more turns to wire coil (solenoid) or increasing the current passing through the wire.

Direct Current (DC)Alternating Current (AC) Current that flows in only one direction through a wire Ex. battery Reverses the direction of the current flow in regular patterns. Ex. Plugging a toaster into wall outlet Direct and Alternating Current