Bell Work: Magnetism 1. When regions of iron atoms are aligned, a magnetic ( block / domain / pole ) is created. 2. When a magnet attracts a paperclip, the clip is ( permanently / temporarily ) magnetized. 3. Name two metals that are not ferromagnetic. 4. A compass lines up ( parallel / perpendicular ) to the magnetic fields. 5. Magnetic fields are strongest near the ( poles / center ) of the magnet.

Earth as a Magnet

Electromagnetism ► ► When there is current through a wire, the filings will form a pattern of concentric circles, around the wire. ► ► A wire with current will create a magnetic field perpendicular to the current flow

Which way? To determine the current and the magnetic field, we use right hand rules. Is the current flowing into or out of the screen? Is the magnetic field rotating clockwise or counter- clockwise?

1 st Right Hand Rule Imagine holding a length of insulated wire with your right hand. Keep your thumb pointed in the direction of the conventional (positive) current. The fingers of your hand circle the wire and point in the direction of the magnetic field. Determines Direction of the Magnetic Field relative to the current

Determine the direction of the current flow.

2 nd Right Hand Rule ► ► Imagine holding an insulated coil with your right hand. If you then curl your fingers around the loops in the direction of the conventional (positive) current, your thumb will point toward the north pole of the electromagnet. Determines Polarity

Which end is North? N

N

Which way is the current flowing?

Solenoid ► ► When a wire is looped several times to form a coil and a current is allowed to flow through the coil, the field around all the loops is in the same direction.

Solenoid ► ► A long coil of wire consisting of many loops is called a solenoid. The field from each loop in a solenoid adds to the fields of the other loops and creates a greater total field strength.

Electromagnets ► ► When there is an electric current in a coil of wire, the coil has a field similar to a permanent magnet. ► ► One end of the electromagnet will attract one end and repel the other end of a magnet. ► ► Thus, the current-carrying coil has a north and a south pole and is itself a magnet. ► ► This type of magnet, which is created when current flows through a wire coil, is called an electromagnet.

► ► The strength of the field is directly related to the current in the coil. ► ► The strength of the field is directly related to the number of coils.   The magnetic field produced by each loop is the same. Because these fields are in the same direction, increasing the number of loops increases the strength of the magnetic field. ► ► The strength of an electromagnet also can be increased by placing an iron rod or core inside the coil.   It increases the magnetic field because the field of the solenoid creates a temporary magnetic field in the core, just as a nearby permanent magnet does when brought near a metal object.

Electromagnetic Induction In 1822 Micheal Faraday wronte a goal in his notebook, it was “Convert magnetism into electricity”. After nearly 10 years he found that he could induce electric current by moving a wire through a magnetic field. The same year, Joseph Henry an American high- school teacher, also showed that a changing magnetic field could produce electric current.

Electromagnetic Induction ► When the wire is moved parallel to the magnetic field or held stationary, there is no current, but when the wire moves up through the field, the current is in one direction. ► When the wire is moves down through the field, the current is in the opposite direction.

Electromagnetic Induction An electric current is generated in a wire only when the wire cuts magnetic field lines. It is relative motion between the wire and the magnetic field that produces a current. Electromagnetic Induction

Electric Generator ► The Electric Generator was invented by Michael Faraday. ► It converts mechanical energy to electrical energy.

Electric Generator ► ► An electric generator consists of a number of wire loops placed in a strong magnetic field. The wire is wound around an iron core to increase the strength of the magnetic field.

Electric Generator ► The iron and wires are called the armature, which is similar to that of an electric motor.

Electric Generator  The armature is mounted so that it can rotate freely in the magnetic field. As the armature turns, the wire loops cut through the magnetic field lines and induce a potential difference. Commonly called the voltage.

Electric Generator The current is greatest when the motion of the loop is perpendicular to the magnetic field (the loop is in the horizontal position). When the loop is in the vertical position, the wire segments move parallel to the field and the current is zero.

Electric Generator The current changes smoothly from zero to some maximum value and back to zero during each half-turn of the loop. Then it reverses direction.

Electric Generators ► ► The entire loop does not contribute to the induced EMF? ► ► If the fourth right-hand rule is applied to segment ab, the direction of the induced current is toward the side of the wire. The same applies to segment cd. ► ► No current is induced along the length of the wire in ab or cd.

Generators and Motors Generators and motors are almost identical in construction, but they convert energy in opposite directions. Generators convert mechanical energy to electrical energy, motors converts electrical energy to mechanical energy.

Transformers ► Transformers are used o increase or decrease AC voltages. ► Transformers change voltages with relatively little loss of energy.

Transformers There are two types of transformers: Step-Up Transformers - the secondary voltage is larger than the primary voltage. Step-Down Transformers - the voltage coming out of the transformer is smaller than the voltage put in the transformer.