ELECTRICITY AND MAGNETISM

Electricity

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

opposite charges attract Law of Conservation of Charge – electric charges can be transferred from object to object, but it cannot be created or destroyed. Positive and negative charges exert forces on each other. + - + - opposite charges attract like charges repel

CONDUCTORS VS. INSULATORS Conductors – material in which electrons move easily Ex. Metals Insulators – material in which electrons are not able to move easily Ex. wood, plastics, 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

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 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 Resistance – tendency for a material to oppose the flow of electrons, changing electrical energy into thermal and light energy. Wet Cell Contains two connected plates made of different metals in conducting solution. Ex. Car Battery

Voltage diff Current = Resistance Making wires thinner, longer or hotter increases resistance All materials have some electrical resistance measured in ohms. (Ω) Ohms Law – current in a circuit equals voltage difference divided by resistance. Voltage diff Current = Resistance

Electrical Circuits

Electrical energy enters your home at the circuit breaker or fuse box and branches out to appliances, wall socket and lights. Circuit breakers – small piece of metal that bends when it gets hot, opening circuit and stopping current flow. Electronic fuse - small piece of metal that melts if current becomes to high, opening circuit

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 closed to magnet)

All magnets have a north pole and a south pole. LIKE POLES REPEL UNLIKE POLES ATTRACT

MAGNETIC MATERIALS Only few metals, such as iron, cobalt, and 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 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 electric current flows through a wire, a magnetic field forms around the wire. Strength of magnetic field depends on the amount of current flowing in the wire. WIRE ELECTRON FLOW

Electromagnets – a temporary magnet made by wrapping a wire coil carrying a current around an iron core. Increases strength of the magnetic field by adding more turns to wire coil (solenoid) or increasing the current passing through the wire Electric motor – a device that changes electrical energy into mechanical energy

DIRECT AND ALTERNATING CURRENT In a simple electric motor, an electromagnet rotates between the poles of a permanent magnet. DIRECT AND ALTERNATING CURRENT Direct Current (DC) – current that flows in only one direction through a wire Ex. A battery Alternating Current (AC) - reverses the direction of the current flow in regular patterns. Ex. Plugging toaster into Wall outlet