IB+MYP+Magnetism

1. Magnetism

Magnetic Domains: Ferromagnetic: Characteristic of substances such as iron, nickel, or cobalt and various alloys that exhibit extremely high magnetic permeability. Atoms align with magnetic fields.

Ferromagnetism: The property of being strongly attracted to either pole of a magnet.

Magnetic forces tend to push all magnetic moments in same direction.

A group of atomic magnets pointing in the same direction is called a magnetic domains.

Solenoid: A loops of insulate wires. When an electric current flows through the solenoid, it produces a strong magnetic field. The resulting magnetic field pattern is like that of a bar magnet but the lines continue through the centre. The poles of the magnet can be determined by the right hand grip rule. (from one-school.net)

Magnetic field: A region in which a magnetic object, placed within the influence of the field, experiences a magnetic force. Magnetic field lines are around a magnet. Any magnetic material placed in the region of these field lines experience a magnetic force in the direction of these lines. Magnetic field lines never cross.

The strength of a field is related to the density of field lines. The magnetic field is strongest close to the poles. The magnetic flux density is the quantity that is used to measure how strong the field is. The unit of magnetic flux density is the **tesla (T)**.
 * Magnetic flux density (B) **

Refer to page 403 and 404, draw magnetic field lines between an N pole and an S pole then between two N or S poles. media type="file" key="MAGNETIC LINES OF FORCE DEMONSTRATION.flv" width="360" height="270" Uses of permanent magnets 1. **M**oving-coil ammeter 2. **M**agnetic door catch 3. **M**oving coil loudspeakers

<span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 21.3333px;">2. Electromagnetism

<span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">**Electromagnetism**: Moving charges (electric currents) produce a magnetic field around it. <span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">You can use the right hand grip rule to determine the direction of the field goes(Stronger field closer to wire).The right hand grip rule (from one-school.net).

<span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">Task 1; Draw Magnetic Field around a wire and a Solenoid (coil)

<span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">Simple eclectromagnet from IOP

<span style="color: #000000; font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">To make an electromagnet stronger <span style="display: block; font-family: "Comic Sans MS",cursive; font-size: 110%; text-align: left; vertical-align: baseline;">1. More C oils <span style="display: block; font-family: "Comic Sans MS",cursive; font-size: 110%; text-align: left; vertical-align: baseline;">2. More C urrent3. Use an iron <span style="color: #0000ff; font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%; vertical-align: baseline;">C ore

<span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">Uses of electromagnets <span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">1. Circuit breaker <span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">2. Magnetic relay <span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">3. Relays: How does a relay work? <span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">4. Magnetic Resonance Imaging (MRI) <span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">5. Electric bell: How does a electric bell work? <span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">>> A model electric bell: A clever application of feedback: a switch that opens and closes due to temporary magnetism in a current-carrying coil of wire.

<span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">When alternating current flow through a long piece of wire which passes between the north and the south pole of a permanent magnet, there is a force acting on it. This is due to the force acting on a current carrying conductor in a magnetic field. This force is caused by the interaction of two magnetic fields around the wire. When the current keeps changing the direction, the force on the wire also keeps changing direction. This is called motor effect. One use of motor effects is a speaker.
 * <span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">Motor Effect **

<span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">If a straight wire is placed in a magnetic field, it also experiences a force. The size of the force is dependent on how strong the field is, how much current is flowing throwing through the wire and the length of the wire. <span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">I is amount of current flowing through the wire <span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">L is the length of the wire ||
 * <span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">Force on a current carrying conductor **
 * <span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">**F = BIL sin θ**, where || <span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">B is magnetic flux density

<span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">The force on the wire may be increased by: <span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">using a larger current <span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">using a stronger magnet

<span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">The direction of the force may be changed by: <span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">changing the direction of the current <span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">changing the direction of the magnetic field

<span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">Looping a wire increases the magnetic field strength: coils <span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">Magnetic fields pass easily through iron <span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">A changing magnetic field induces a current in a conductor

<span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 21.3333px;">3. Electromagnetic Induction

<span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">Electromagnetic induction is a production of electricity using a magnetism. <span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">Changing one current in a primary coil forms magnetic field around it. The change of the magnetic field induces currents in the secondary coil.

<span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">A <span style="color: #0000ff; font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">changing current in <span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;"> the primary coil produces a <span style="color: #0000ff; font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">changing magnetic field <span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;"> in the core. This changing magnetic field <span style="color: #0000ff; font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">induces <span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;"> a changing current in the secondary coil.

<span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">The magnetic field produced by an alternating current in one coil induces a similar current in the other coils.

<span style="font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 110%;">Three ways to produce more electricity <span style="font-family: &#39;Comic Sans MS&#39;,cursive;">1. Stronger **M** __ agnet __ <span style="font-family: &#39;Comic Sans MS&#39;,cursive;">2. **M**ore number of c __ oils __ <span style="font-family: &#39;Comic Sans MS&#39;,cursive;">3. **M**ove the magnet or coils __ faster __

**<span style="font-family: &#39;Comic Sans MS&#39;,cursive;">Faraday's Law of Electromagnetic Induction **
<span style="font-family: &#39;Comic Sans MS&#39;,cursive;">Any change in the magnetic environment of a coil of wire will cause a voltage=emf to be induced in the coil.

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<span style="font-family: &#39;Comic Sans MS&#39;,cursive;">When an emf generated by a change in magnetic flux, the direction of the induced e.m.f. and hence the induced current in a closed circuit, is always such that its magnetic effect opposes the motion or change producing it. => Changes in magnetic flux generate electromotive force. System do not like a change. =====


 * <span class="wiki_link_ext">Faraday's law from HyperPhysics**



//Faraday's Electromagnetic Lab//** from Phet media type="custom" key="13747940" 1. Investigate Faraday's Electromagnet Lab paying attention to what you can change and what tools you can use to make measurements. We will using the Bar Magnet and Electromagnet tabs for this activity and the other tabs later.
 * Predict the direction of the magnetic field for different locations around a bar magnet and an electromagnet.
 * Compare and contrast bar magnets and electromagnets.
 * Identify the characteristics of electromagnets that are variable and what effects each variable has on the magnetic field's strength and direction.
 * Relate magnetic field strength to distance quantitatively and qualitatively.
 * Compare and contrast how both a light bulb and voltmeter can be used to show characteristics of the induced current.

2. Read the first four learning goals and design experiments using the simulation that would help you learn thee specific things. You do not have to write the procedures, but be prepared to explain to the teacher or another student your designs. Write a document that gives evidence that you can meet the learning goals. (Include illustrations drawn by hand.)

A. Pretend you and your lab partner are designers for the PhET simulations and want to make a simulation for students to investigate gravity fields. Think about what you know about gravity and what kinds of experiments a student might want to do to learn about gravity. You may have to refresh your memory by using the text. Draw a design, by hand, for a gravity simulation. Explain why you included each component and explain at least one experiment that a student could do.
 * __//Challenge//__**

B. Compare and contrast the fields of gravity and magnets qualitatively. => To check your writing, each person will meet with a person from a different group. Read each others paragraphs and talk about your reasoning. Write one new paragraph that you both agree is well done.

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<span style="font-family: &#39;Comic Sans MS&#39;,cursive;">(Transformers consist of two coils of conducting material, such as wire, wrapped around a common soft core, often made of iron. The primary coil is connected to an AC supply. This causes a changing magnetic field inside the coil. This field is made stronger by the presence of the soft iron core which itself becomes magnetic temporarily. Since the secondary is wound around the same core, it will have a changing magnetic field within it, which induces an emf in its coils). =====

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<span style="font-family: &#39;Comic Sans MS&#39;,cursive;">- A transformer where the voltage <span style="color: #0000ff; font-family: &#39;Comic Sans MS&#39;,cursive;">rises <span style="font-family: &#39;Comic Sans MS&#39;,cursive;"> is called a **step-** <span style="color: #ffffff; font-family: &#39;Comic Sans MS&#39;,cursive;">up <span style="font-family: &#39;Comic Sans MS&#39;,cursive;"> transformer. =====

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<span style="font-family: &#39;Comic Sans MS&#39;,cursive;">- A transformer where the voltage <span style="color: #0000ff; font-family: &#39;Comic Sans MS&#39;,cursive;">falls <span style="font-family: &#39;Comic Sans MS&#39;,cursive;"> is called a **step-** <span style="color: #ffffff; font-family: &#39;Comic Sans MS&#39;,cursive;">down <span style="font-family: &#39;Comic Sans MS&#39;,cursive;"> transformer. =====

<span style="font-family: &#39;Comic Sans MS&#39;,cursive;">*The ratio of primary and secondary **voltage** is the same as the ratio of primary and secondary **coils**.

 * =====<span style="font-family: &#39;Comic Sans MS&#39;,cursive;">Input (primary) voltage ===== || =====**=**===== || =====<span style="font-family: &#39;Comic Sans MS&#39;,cursive;">Primary turns ===== ||
 * =====<span style="font-family: &#39;Comic Sans MS&#39;,cursive;">Output(secondary) voltage ===== ||  || =====<span style="font-family: &#39;Comic Sans MS&#39;,cursive;">Secondary turns ===== ||

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//V// p / //V// s = <span style="font-family: &#39;Trebuchet MS&#39;,Helvetica,sans-serif; font-size: 150%;">//N// p /<span style="font-family: &#39;Trebuchet MS&#39;,Helvetica,sans-serif; font-size: 150%;"> //N// s=====

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<span style="color: #000000; font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 14px;">Because transformers rely on induction (caused by changing fields), they only work with alternating current (a.c.) =====

**<span style="color: #000000; font-family: &#39;Comic Sans MS&#39;,cursive; font-size: 14px;">Why do we need transformers? **
Current flowing through wires causes them to get hot and energy is lost. Keeping the current low means electricity can be transported long distances without losing too much energy. However, in order to send a large quantity of energy, high voltages are needed.

<span style="font-family: Arial,Helvetica,sans-serif;">DEFINITIONS AND CONCEPTS

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">MAGNETIC FIELD: The area around a magnet where another magnet would feel a force. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">MAGNETIC FIELD LINES: Show the direction of the magnetic field. The lines run from North to South. Where the field is strong, they are close together. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">INDUCED MAGNETISM: A magnetic material can be magnetised by being placed in a magnetic field. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">INDUCED e.m.f.: Any influence that causes electric charges flow as a result of electromagnetic induction. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">INDUCED current: An electric current that flows as a result of an induced e.m.f. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">ELECTROMAGNET: A current-carrying coil of wire (SOLENOID) often wrapped around a soft magnetic core which produces a magnetic field quite like a bar magnet with uniform field lines inside. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">MOTOR EFFECT: A current-carrying wire in a magnetic field experiences a force. This effect is applied in simple DC motors, loudspeakers and ammeters. The force is greater when the field or current are greater. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">ELECTROMAGNETIC INDUCTION: A changing magnetic field through a conductor will induce a voltage in the conductor. The voltage is greater when the change is greater (larger field or faster movement). <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">GENERATOR/ DYNAMO: A device which induces a voltage when a magnet rotates in a coil or vice versa. A larger voltage is induced when the rotation is faster, the field greater or there are more turns in the coil. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">TRANSFORMER: A device which allows an input AC voltage to be stepped up or down. <span style="font-family: Arial,Helvetica,sans-serif;">HARD AND SOFT MAGNETIC MATERIALS: Materials which are difficult to magnetise and de-magnetise. Soft materials are easy to magnetise and de-magnetise. <span style="font-family: Arial,Helvetica,sans-serif;">High temperature: Random orientation <- Curie Point Temperature -> Low temperature: Aligned <span style="font-family: Arial,Helvetica,sans-serif;">Hard(Steel): Alignment stays <span style="font-family: Arial,Helvetica,sans-serif;">Soft(Iron) : Transient

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">Magnetism

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">1 units <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">2 recall that magnets repel and attract other magnets, and attract magnetic substances <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">3 recall the properties of magnetically hard and soft materials. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">4 understand the term ‘magnetic field line’. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">5 understand that magnetism is induced in some materials when they are placed in a magnetic field ) <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">6 sketch and recognise the magnetic field pattern for a permanent bar magnet and that between two bar magnets <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">7 know how to use two permanent magnets to produce a uniform magnetic field pattern

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">Electromagnetism

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">8 recall that an electric current in a conductor produces a magnetic field round it <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">9 describe the construction of electromagnets <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">10 sketch and recognise magnetic field patterns for a straight wire, a flat circular coil and a solenoid when each is carrying a current <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">11 appreciate that there is a force on a charged particle when it moves in a magnetic field as long as its motion is not parallel to the field <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">12 recall that a force is exerted on a current-carrying wire in a magnetic field, and, how this effect is applied in simple d.c. electric motors and loudspeakers <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">13 predict the direction of the resulting force when a wire carries a current perpendicular to a magnetic field <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">14 recall that the force on a current-carrying conductor in a magnetic field increases with the strength of the field and with the current

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">Electromagnetic induction

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">15 recall that a voltage is induced in a conductor when it moves through a magnetic field or when a magnetic field changes through a coil; also recall the factors which affect the size of the induced voltage <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">16 describe the generation of electricity by the rotation of a magnet within a coil of wire and of a coil of wire within a magnetic field; also describe the factors which affect the size of the induced voltage <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">17 recall the structure of a transformer, and understand that a transformer changes the size of an alternating voltage by having different numbers of turns on the input and output sides <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">18 explain the use of step-up and step-down transformers in the large-scale generation and transmission of electrical energy <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">19 recall and use the relationship between input (primary) and output (secondary) voltages and the turns ratio for a transformer <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">20 recall and use the relationship for 100% efficiency