Unit 3 Lesson 5 Electromagnetism

Home , Electric current, Electromagnetism, Magnetic field

Magnetic Attraction What is electromagnetism?

• In 1820, Danish physicist Hans Christian Oersted observed a magnet move in the presence of an electric current.

• Oersted hypothesized that the electric current had produced a magnetic field. Later experiments confirmed his hypothesis, demonstrating the relationship between electricity and magnetism.

• Electromagnetism results when electric currents and magnetic fields interact with each other.

How can you make a magnet using current? • A coil of wire that carries an electric current, and therefore produces a magnetic field, is called a solenoid. The more loops, the stronger the magnetic field.

How can you make a magnet using current? • Wrapping a solenoid around an iron core makes an electromagnet, which combines the magnetic field of the solenoid with the magnetic field of the magnetized iron core.

• Adding loops to the solenoid or increasing the electric current strengthens the electromagnet.

What are some uses for electric magnets? • Electromagnets are useful for lifting and moving large metal objects containing iron. When current runs through the solenoid coils, it creates a magnetic field that attracts the metal objects. Turning off the current turns off the magnetic field so that the metal can be easily dropped in a new place.

• Powerful electromagnets can raise a maglev train above its track. Just as poles of a bar magnet repel each other, electromagnets in the train and track repel each other when the electric current is turned on.

What are some uses for electric magnets? • A galvanometer is a meter that measures the strength and direction of an electric current in a wire.

• A galvanometer contains an electromagnet between the poles of a permanent magnet. When current is applied to the electromagnet, the two magnetic fields interact and cause the electromagnet to turn.

• The indicator, attached to the electromagnet, moves to one side of the zero on the scale, indicting the strength and direction of the current.

What are some uses for electric magnets? • The indicator on a galvanometer shows current direction and strength.

A Look Inside • Magnetic resonance imaging (MRI) machines use powerful electromagnets and radio waves to produce detailed images of the body’s interior.

• Doctors use MRI scans to diagnose many conditions, including broken bones and strained tendons.

• Some MRI scans help scientists understand how the brain works.

Let’s Motor! How do motors work?

• An electric motor changes electrical energy into mechanical energy.

• Electric motors range in size from large motors, used to power Ferris wheels, to small motors used in computer cooling fans. Almost every time a device uses electricity to make something move, there is a motor involved.

How do motors work?

• A simple motor has a coil or loop of wire called an armature mounted between the poles of a magnet. The armature becomes an electromagnet when current passes through it.

• The armature rotates because its poles are pushed and pulled by the opposite poles of the magnet. The armature turns until its north pole is opposite the magnet’s south pole.

• Then, a device called a commutator reverses the direction of the current in the wire, causing the armature to complete its turn.

How do motors work?

• Electric motors are very similar to galvanometers. However, in a motor, the electromagnet is made to rotate all the way around instead of back and forth in the magnetic field.

A New Generation What are some uses for induction?

• Using a magnetic field to create an electric current in a wire is called electromagnetic induction.

• When electric charges move through a wire, the wire carries a current. Magnetic force from a magnet moving inside a coil of wire can make the electric charges in the wire move. When the magnet stops moving inside the coil, the electric current stops.