Transcript Magnets
Question • Without using your book or electronic devices: • Make a definition of what a magnet is. Magnets What is a magnet? •A magnet is an object that attracts certain materials usually objects made of iron or steel. •A magnet has two ends called magnetic poles or just poles for short. •A magnet’s pull is strongest at the poles. •Poles are usually marked North and South. Types of Magnets • There are three types of magnets. • Permanent • Temporary • Electromagnet Permanent Magnets • These are naturally occurring pieces of a mineral called magnetite. It also has another name known as “lodestone”. • Key features: • • • • Naturally occurring Magnetic field cannot be turned off Magnetic field has a specific direction Cannot increase the field strength Temporary Magnets • These are pieces of iron, steel, or cobalt that have been temporarily turned into a magnet. • Key features: • Occurs when a permanent magnet is rubbed along a piece of iron, steel, or cobalt • Magnetic field cannot be turned off, however it doesn’t last long • Magnetic field has a specific direction which is determined by the permanent magnet. • Field strength is determined by strength of permanent magnet used on it. Electromagnets • Will be discussed in detail later. •Magnetic Forces •Forces you feel when playing with magnets can be pushes or pulls. •A magnetic field is the space all around a magnet where the force of the magnet can act. •You can’t see the field • Forces between magnetic poles are like forces between electric charges. • Opposite magnetic poles attract, and like poles repel. North and South poles attract. • North and North poles repel or push away. • South and South poles repel or push away. How does it work? Magnetic Force • With the charges lined up it creates a greater amount of force that can react at a distance. What about a temporary magnet? • Remember everything that is matter has charges in them. However until those charges line up or move in the same direction they have very little force. Compass •The North and South seeking poles of magnets have been helpful to people for hundreds of years to find direction. • The first magnets used were made of heavy natural material called a lodestone, which is a mineral magnetite. • A compass today uses a lightweight magnetic needle that is free to turn. • A compass needle points along an imaginary line connecting the North and South poles. This is because earth is like a giant magnet. •Field lines of earth’s magnetic field come together close to the planet’s North and South poles. •The north-seeking pole of the freemoving magnet in the compass points to Earth’s North Pole. Electromagnetism Section 1: What is Electromagnetism? What is electromagnetism? • (1820) Hans Christian Oersted produced a current in a wire during a lecture. • When he brought a compass near the wire, the compass changed direction. • Whenever he turned on the current in the wire, the compass needles lined up around the write in the shape of a circle. Electric Current & Magnetism • How can you observe electromagnetism? • Compass & electric current • A compass needle normally points north because it aligns itself with Earth’s magnetic field • The needles of compasses surrounding a current will align with the current, producing a circle Electric Current & Magnetism • Wherever there is electricity, there is magnetism • An electric current produces a magnetic field • This relationship is called electromagnetism What do they look like? • An electromagnets can be made out of a variety of materials but they all have the following: • Voltage source (battery or other source) • A magnetic core • Wire wrapped around the core. This is known as a solenoid. The more times the wire is wrapped around the core the greater the strength of the magnet. Electromagnets day 2 Ball Drop Review The Magnetic Field • The magnetic field produced by a current has three distinct characteristics: 1. The field can be turned on and off 2. The field can have its direction reversed 3. The field can have its strength changed The Magnetic Field • You can turn a magnetic field produced by a current on and off… • How can you turn the magnetic field off? • Simply by turning the current off! The Magnetic Field • You can change the direction of a magnetic field… • How can you change the direction? • Simply by reversing the direction of the current! Solenoids • You can change the strength of a magnetic field produced by a current… • How can you change the strength? • Simply by looping, or winding, the wire of the wire! • The strength will increase as the number of loops or coils increases • A solenoid is a coil of wire with a current. Electromagnets • A solenoid with a ferromagnetic core is called an electromagnet. • The magnetic field of an electromagnet can be hundreds or thousands of times stronger than the magnetic field of the current alone • Basically, an electromagnet is a strong magnet that can be turned on or off. Electromagnets • You can increase the strength of an electromagnetic field… 1. 2. 3. 4. Increase the current in the solenoid Add more loops of wire to the solenoid Wind the coils of the solenoid closer together Increase the strength of an electromagnet by using a stronger ferromagnetic material for the core Simulation • http://phet.colorado.edu/en/simulation/legacy/ma gnets-and-electromagnets Does theory match up??? • Test whether adding more wraps does create a stronger magnetic field. Common Electromagnets • Audiotapes • Videotapes • Computer hard drives • Credit cards • Doorbells • Radios • Refrigerators Electric Motors Electric Motor • An electromagnet is the basis of an electric motor • An electric motor is all about magnets and magnetism: A motor uses magnets to create motion. • Opposites attract and likes repel. Inside an electric motor, these attracting and repelling forces create rotational motion. • A motor is consist of two magnets. Vertical position of the loop: Rotation N S