Flash Cards (physical science)

magnetic force

Depending on which ends of the magnets are close together, the magnets either repel or attract each other. The strength of the force between two magnets increases as magnets move closer together and decreases as the magnets move farther apart.

earths magnetic field

A compass can help determine direction because the north pole of the compass needle points north. This is because Earth acts like a giant bar magnet and is surrounded by a magnetic field that extends into space.Just as with a bar magnet, the compass needle aligns with Earth's magnetic field lines.

magnetic domains

Groups of atoms with aligned magnetic poles are called magnetic domains. Each domain contains an enormous number of atoms, yet the domains are too small to be seen with the unaided eye. Because the magnetic poles of the individual atoms in a domain are aligned, the domain itself behaves like a magnet with a north pole and a south pole.

electromagnets

An electromagnet is a temporary magnet made by wrapping a wire coil carrying a current around an iron core. When a current flows through a wire loop, the magnetic field inside the loop is stronger than the field around a straight wire. A single wire wrapped into a cylindrical wire coil is called a solenoid.

earths magnetic poles

Currently, Earth's south magnetic pole is located in northern Canada about 1,500 km from the geographic north pole. Earth's magnetic poles move slowly with time. Sometimes Earth's magnetic poles switch places so that Earth's south magnetic pole is the southern hemisphere near the geographic south pole.

lining up domains

Even though each domain behaves like a magnet, the poles of the domains are arranged randomly and point in different directions. As a result the magnetic fields from all the domains cancel each other out. If you place a magnet against the same nail, the atoms in the domains orient themselves in the direction of the nearby magnetic field. The like poles of the domains point in the same direction and no longer cancel each other out. The nail itself now acts as a magnet. The nail is only a temporary magnet. Paper clips and other objects containing iron also can become temporary magnets.

galvanometers

In a galvanometer, the electromagnet is connected to a small spring. Then the electromagnet rotates until the force exerted by the spring is balanced by the magnetic forces on the electromagnet. Changing the current in the electromagnet causes the needle to rotate to different positions on the scale.

how magnets interact

Two magnets can either attract or repel each other. Two north poles or two south poles of two magnets repel each other. However, north poles and south poles always attract each other. When two magnets are brought close to each other, their magnetic fields combine to produce a new magnetic field.

electric motors

A fan uses an electric motor, which is a device that changes electrical energy into mechanical energy. The motor in a fan turns the fan blades, moving air past your skin to make you feel cooler. Almost every appliance in which something moves contains an electric motor.

generators

A generator uses electromagnetic induction to transform mechanical energy into electrical energy. An example of a simple generator is shown. In this type of generator, a current is produced in the coil as the coil rotates between the poles of a permanent magnet.

magnetic field

A magnet is surrounded by a magnetic field. A magnetic field exerts a force on other magnets and objects made of magnetic materials. The magnetic field is strongest close to the magnet and weaker far away. The magnetic field can be represented by lines of force, or magnetic field lines. A magnetic field also has a direction. The direction of the magnetic field around a bar magnet is shown by the arrows.

permanent magnets

A permanent magnet can be made by placing a magnetic material, such as iron, in a strong magnetic field. The strong magnetic field causes the magnetic domains in the material to line up. The magnetic fields of these aligned domains add together and create a strong magnetic field inside the material.

transformers

A transformer is a device that increases or decreases the voltage of an alternating current. A transformer is made of a primary coil and a secondary coil. These wire coils are wrapped around the same iron core. As an alternating current passes through the primary coil, the coil's magnetic field magnetizes the iron core. The magnetic field in the primary coil changes direction as the current in the primary coil changes direction. This produces a magnetic field in the iron core that changes direction at the same frequency. The changing magnetic field in the iron core then induces an alternating current with the same frequency in the secondary coil. The changing magnetic field in the iron core then induces an alternating current with the same frequency in the secondary coil. The voltage in the primary coil is the input voltage and the voltage in the secondary coil is the output voltage. The output voltage divided by the input voltage equals the number of turns in the secondary coil divided by the number of turns in the primary coil.

magnetic poles

Magnetic poles are where the magnetic force exerted by the magnet is strongest. All magnets have a north pole and a south pole. For a bar magnet, the north and south poles are at the opposite ends. The two ends of a horseshoe-shaped magnet are the north and south poles. A magnet shaped like a disk has opposite poles on the top and bottom of the disk. Magnetic field lines always connect the north pole and the south pole of a magnet.

magnets

More than 2,000 years ago Greeks discovered deposits of a mineral that was a natural magnet. The mineral is now called magnetite. In the twelfth century Chinese sailors used magnetite to make compasses that improved navigation. Today, the word magnetism refers to the properties and interactions of magnets.

magnetic field direction

When a compass is brought near a bar magnet, the compass needle rotates. The force exerted on the compass needle by the magnetic field causes the needle to rotate. The compass needle rotates until it lines up with the magnetic field lines. The north pole of a compass points in the direction of the magnetic field. This direction is always away from a north magnetic pole and toward a south magnetic pole.

transmitting electrical energy

When the electric energy is transmitted along power lines, some of the electrical energy is converted into heat due to the electrical resistance of the wires. The electrical resistance and heat production increases as the wires get longer. One way to reduce the heat produced in a power line is to transmit the electrical energy at high voltages, typically around 150,000 V. Electrical energy at such high voltage cannot enter your home safely, nor can it be used in home appliances. A transformer is used to decrease the voltage.

magnetic materials

You might have noticed that a magnet will not attract all metal objects. Only a few metals, such as iron, cobalt, or nickel, are attracted to magnets or can be made into permanent magnets. What makes these elements magnetic? Remember that every atom contains electrons. In the atoms of most elements, the magnetic properties of the electrons cancel out. But in the atoms of iron, cobalt, and nickel, these magnetic properties don't cancel out. Even though these atoms have their own magnetic fields, objects made from these metals are not always magnets.