ELECTRICITY and MAGNETISM. by pablo gomez

SCIENCE 6.

UNIT 7. ELECTRICITY & MAGNETISM.

CONTENTS: 1.– ELECTRICITY: Atom. 1.1.– Static electricity. 1.2.- Conductors and insulators. 1.3.- Components of an electrical circuit. 1.4.- Effects of electricity. 1.5.– Safety rules. 2.– MAGNETISM: 2.1.– Magnets. Types of magnets. 2.2.- Magnetic poles. 2.3.– Magnetic field. Earth’s magnetic field. 2.4.- Electromagnets. 2.5.– Electric motor. Electric generator.

C.E.I.P. SANTA ANA (Madridejos)

ELECTRICITY is the flow of electrons from atom to atom in a conductor substance. Electrons jump from atom to atom

2 Electric current.

1.– ELECTRICITY: All substances are formed by molecules and atoms. The center of an atom is called nucleus. It is made of particles called protons and neutrons. Protons have a positive charge. Atoms have got an electron shell formed by electrons. Electrons have a negative charge. They are much smaller than the nucleus. Electrons are spinning around the nucleus. If the size of the nucleus would be like a tennis ball, the electron shell would be like a football stadium. Electricity current is the flow of electrons from atom to atom in a conductor substance. 1.1.– Static electricity: All objects contain electrical charges. These charges are positive and negative. Static electricity occurs when the electrons from one object jump to another object. A.- If an object contains more positive charges than negative ones, it has a positive charge. B.- If the object has more negative charges than positive ones, it has a negative charge. Example: If we rub a balloon or a plastic ruler with a piece of cloth or our own hair, the balloon will be charged with electricity (static electricity). We will observe that the balloon can attract small pieces of paper or hair. This reaction is because the balloon or the ruler is charged and attract little pieces of paper or hair that have got the opposite charge. If we charge two balloons with the same piece of cloth, they will repel each other .

Proton

Nucleus Neutron

Electron

Static electricity occurs when the electrons from one object jump to another object. In Static electricity charges don’t move or flow.

Static electricity attracts little pieces of paper or hair.

.- Opposite electrical charges attract each other. .- Same electrical charges repel each other. We can feel static electricity when we get out from a car, and we touch the metal door. We sometimes feel a shock. During a storm there is a lot of static electricity in the air.

Electrons from the cloud fall down to the Earth (lightning).

9 Lightning

USEFUL WORDS: .– electricity .– neutron .– positive charge .– static electricity .– to attract

.– flow .– proton .– negative charge .– electron shell .– to repel

.– atom .– electron .– current .- to rub .– lightning

2 C.E.I.P. SANTA ANA (Madridejos)

.– Conductors permit an electric current to pass through them.

1.2.– Conductors and insulators:

.– Insulators don’t permit an electric current to pass through them.

Not all substances react in the same way to an electric current. There are two groups: a.– Conductors: are materials that permit an electric current to pass through them. Some examples are metals like copper, steel, aluminium, silver, water, human body… b.– Insulators: are materials that don’t permit an electric current to pass through them. Electrons from their atoms can’t move easily. Some examples are plastic, rubber, wood, clay, glass, dry air... 1.2.– Components of an electrical circuit:

Copper (conductor)

Plastic (insulator) 11

An Electrical circuit is a group of objects that generate, distribute and use electricity.

An electric circuit could have lots of components, because it could be very complicated (every house has got a circuit). But all circuits must have these components: a.– A Generator: that produces electric current. .- Power stations produce electricity to houses, towns... .– Battery: gives electricity to a car, or a simple circuit. b.- Wires: that transport electric current from the generator to other components. They are usually made of copper wire, covered by an insulator (plastic).

Switch (open)

Generator (battery)

Wires Receptor

c.– A Switch: that interrupts the flow of the electric current. When the circuit is closed, electricity can pass throught the circuit, when the circuit is open electricity can’t move.

(light bulb)

Simple electric circuit (photo)

d.– Receptors: receive and transform electricity in another form of energy. .– Light bulb transforms electricity into light. .– Electric motor transforms electricity into kinetic energy. .– Electric heater transforms electricity into heat. .– TV, radio, laptop, microwave oven... Simple electric circuit (diagram)

Simple electric circuit (drawing)

switch battery 17 18

Light bulb

Electric circuit symbols

USEFUL WORDS: .– conductor .– wires

.– insulator .– switch

electron flow

.- copper .– receptors

.– generator .– light bulb

C.E.I.P. SANTA ANA (Madridejos)

1.4.– Effects of electricity:

Electricity effects: light, heat, electromagnetism, sound, movement...

Electricity can be easily transformed into other types of energy, and it can produce some effects. a.– Light: When electrons pass through a substance produce friction. This friction heats the substance, and it can be incandescent and produces light. Light bulbs have got a tungsten filament that produces light. Flourescent tubes have a gas inside that can be incandescent and produces light too.

Tungsten filament

Inert gas (inside the bulb)

Glass bulb Light bulb (light)

23 Electric heater (heat)

Screw cap

Electric resistance

b.– Heat: when electrons pass through the wires, produce a friction due to the resistance from the wire. This friction produces heat, that we can use to heat a room, to toast a piece of bread... Controls

A magnetic field is the portion of space near a magnetic object in which magnetic forces can be detected. 24

Protection

Piece of iron

Battery

c.– Electromagnetism: When a current of electrons flows through a wire, it generates a magnetic field. The magnetic field can be increased if you roll up the wire around a piece of iron. This allows more current to flow through a smaller distance and increases the power of the magnetic field. The piece of iron becomes into a magnet when the current is working, so it can attract small pieces of iron (paper clips, nails…) Rolled up wire

25 Membrane

d.– Sound: speakers from a radio, or a phone… have got an electromagnet that produces vibrations on a membrane. This is the way that electricity produces sounds. Electromagnet

Speaker (sound)

Electromagnet (magnetism)

Rotor

Shaft

e.– Movement: An electric motor is a machine with an electromagnet that can move and converts electricity into movement. 1.4.– Safety rules when we use electricity:

Electric motor (movement)

There are some rules to follow when we use electricity, because it can be very dangerous. ELECTRICITY CAN BE DANGEROUS!!!

1.– Never play with electricity. You only can use small batteries. 2.– When you use a device, you must always follow the instructions. 3.– Don’t insert anything into a socket. 4.– Don’t plug lots of devices in the same socket.. 5.– Don’t touch electric devices if you are wet. 6.– Never put electronic devices into the water, specially if they are plugged in.

.–magnetic field .– device

.– electromagnetism .-socket

.- speaker .- to plug

C.E.I.P. SANTA ANA (Madridejos)

MAGNETISM is the property of some 2.– MAGNETISM: substances to attract some metals like iron. Magnetism is the property of some substances to attract some This substances are called magnets. metals like iron or mixtures of iron such steel.

2.1.– Magnets: are objects that attract iron and some other metals. There are two types of magnets: a.- Natural magnets: attract iron and other metals by their own composition: magnetite. b.- Artificial magnets: they are man-made. They are made of steel which get magnetism when they come in contact with other magnets (touch, or friction), or by an electrical current.

33 Magnetite and a man-made magnet attract a nail.

2.2.– Magnetic poles: Magnets can be different in shapes or size, but all magnets have two poles. Magnet poles are the areas of a magnet with the strongest magnetism. Poles are at the ends of the magnet, and they are called north pole (N) and south pole (S).

There are two poles: N (north) & S (south). * Opposite poles attract. * Same poles repel.

35 36 Same poles repels / Opposite poles attract.

2.3.– Magnetic field. Earth’s magnetic field. 37

2.3.1.- A magnetic field is the portion of space surrounding a magnet or an electrical current in which magnetic forces can be detected.

There are magnetic forces that attract or repel parts of other magnets or pieces of some metals inside this space. These magnetic forces goes from the N pole to the S pole. Magnetic poles can’t be isolated, so if a magnet breaks in two pieces, we will have two smaller magnets, both of them with its own north and south poles. 2.3.2.– Earths’s magnetic field is the magnetic field generated by the motion of molten iron in the core of Earth. So our planet works like an enormous magnet. Geographical poles and magnetic poles on Earth are near each other but they don’t totally fit. A compass is an instrument that points at the Earth’s magnetic poles. It is used for orientation and navigation.

Lines of forces in a magnetic field. From N pole to S pole.

Geomagnetic field is used by animals to guide and navigate (homing pigeons, migratory birds, turtles…)., and protects our planet from radiations from the Sun and Space.

Solar wind

Geomagnetic field

Earths’s magnetic field is the magnetic field generated by the core of the Earth. 38

Geomagnetic field protects our planet from radiations from the Sun & Space.

.– magnet .– man-made .– repel .– north pole .– Earth’s magnetic field

40 .– attract .– south pole .– compass

C.E.I.P. SANTA ANA (Madridejos)

Electromagnet is formed by a piece of iron surrounded by a coil of wire. The iron becomes a magnet when an electrical current is on.

2.4.– Electromagnets:

Electromagnets are temporary magnets in which the magnetic field is produced by an electric current. The magnetic field disappears when the current is turned off. We can make an electromagnet if we coil an insulated wire around a piece of iron that becomes magnetized when the electric current flows through the wire. Structure of an electromagnet.

Electromagnets are components of other electrical devices, such as motors, generators, loudspeakers… They are also used in industry for picking up and moving heavy iron objects. This crane uses a big electromagnet.

2.5.1.– Electric motors: Electric motors transform electric energy (through an electromagnet which is spinning by the attraction and repelling forces with another magnet) into movement. ELECTRICITY

MAGNETISM

MOVEMENT

An electric motor is an electrical machine that converts electrical energy into mechanical energy .

2.5.2.– Electric generators:

43 44 Structure of an electric motor. Electric motor from inside.

Electromagnetic induction consists of the generation of electrical energy from a changing magnetic field. If an induction coil (that is a wire rolled around a piece of iron) moving near a magnet, produces a flow of electrons (an electrical current). This is the reason because generators and dynamos produce electricity. MOVEMENT

MAGNETISM

Structure of an electric generator.

ELECTRICITY

An electric generator is a machine that converts mechanical energy into electrical energy. .– electromagnet .– to spin .– dynamo

.- coil .– crane .– electric motor .– electric generator

Electric generator.

Electricity

Rolled