Lecture 58 – Lecture 59 Electricity and Magnetism Ozgur Unal NIS – PHYSICAL SCIENCE Lecture 58 – Lecture 59 Electricity and Magnetism Ozgur Unal

Electric Current and Magnetism In 1820, Danish physicist and teacher Hans Christian Oersted found that electricity and magnetism are related. While doing a demo involving electric current he noticed that the flow of electric current affected the orientation of the compass needle  electric current creates a magnetic field Today, we know that moving charges create magnetic field. The direction of the magnetic field can be found using the right hand rule. http://www.absorblearning.com/media/attachment.action?quick=7d&att=522

Electromagnets An electromagnet is a temporary magnet made by wrapping a wire coil carrying a current around an iron core. A single wire wrapped into a cylindrical wire coil is called a solenoid. The magnetic field inside a solenoid is stronger than the field in a single loop. If the solenoid is wrapped around an iron core, an electromagnet is formed. The solenoids magnetic field magnetizes the iron core  stronger magnetic field (100 times)

Properties of Electromagnets Electromagnets are temporary magnets  magnetic field is present as long as the current flows The strength of the magnetic field can be increased by adding more turns to the solenoid OR by increasing the current. Since electromagnets have south and north poles, they can attract or repel other magnets.

Making an Electromagnet Rotate An electromagnet can be made to rotate using another magnet.

Electromagnets in Speakers In a speaker there is an electromagnet that vibrates the speaker cone  production of sound

Galvanometers Galvanometers are devices that use an electromagnet to measure electric current.

Electric Motor Consider these electrical devices in the pictures. What type of energy do these devices convert electrical energy into? Electrical energy is converted into mechanical energy. These appliances all contain an electric motor. An electric motor is a device that changes electrical energy into mechanical energy.

Electric Motor A simple electric motor contains a wire coil, a permanent magnet and a source of electric current (such as battery). It also includes components called brushes and a commutator. The brushes are conducting pads conencted to the battery. A commutator is a conducting metal ring that is split. The brushes and the commutator form a closed circuit between the battery and the coil.

Electric Motor When current flows in the coil, the forces between the coil and the permanent magnet cause the coil to rotate. Reversing the direction of the current twice at each rotation makes the electromagnet rotate continuously. Check out Figure 15!! http://www.animations.physics.unsw.edu.au/jw/electricmotors.html#mandg http://www.walter-fendt.de/ph14e/electricmotor.htm