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Electromagnetism Magnetism

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Magnetic Field Definition Electric Field A region of space in which a charged particle experiences an electric force. Magnetic Field A region of space in which a moving charged particle experiences a magnetic force. How must it move? Discuss later.

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Law of Poles Review Law of Charges Opposites – Attract Likes – Repel Law of Poles Opposites – Attract Likes – Repel

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Magnetic Field Lines Rules 1.Point North to South on the EXTERIOR of a magnet. 2.Point South to North on the INTERIOR of a magnet. 3.Form closed loops. 4.Never cross.

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Magnetic Field Lines Examples 1.Two like poles 2.Two opposite poles 3.Bar magnet 4.Earth

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B Field of a Current-Carrying Wire 1 st Right Hand Rule Using your right-hand: 1.Point your thumb in the direction of the conventional current. 2.Curl your fingers into a half-circle around the wire, they point in the direction of the magnetic field, B Field Notation Out of the page. Into the page.

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B Field of a Current-Carrying Wire Examples 1.Current flowing straight towards you. 2.Electrons flowing away from you. 3.Current flowing away from you. 4.Current flowing right-to-left. 5.Electrons flowing left-to-right. 6.Electrons flowing straight towards you. 7.Current flowing left-to-right. 8.Electrons flowing right-to-left.

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B Field of a Current-Carrying Loop 2 nd Right Hand Rule Using your right-hand: 1.Point your thumb in the direction of the conventional current. 2.Curl your fingers into the loop, they point in the direction of the magnetic field, B Field Notation Out of the page. Into the page.

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B Field of a Current-Carrying Loop Examples 1.Current flowing clockwise. 2.Electrons flowing counterclockwise. 3.Electrons flowing down the front edge 4.Current flowing counterclockwise. 5.Current flowing down the front edge. 6.Current flowing up the front edge. 7.Electrons flowing clockwise. 8.Electrons flowing up the front edge.

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Tangent Galvanometer Lab PreLab 1.Discuss set-up. 2.Discuss aligning the plane of loops. 3.Discuss how to wind the loops. 4.Discuss how to connect batteries. 5.Discuss how to measure current. 6.Discuss how to measure the angle. 7.Discuss B calculation. 8.Discuss average calculations.

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Tangent Galvanometer Lab Post Lab 1.When the current is flowing through the loops, what are the two magnetic fields affecting the compass? Draw an overhead view of the influencing fields. 2.Calculate the average B Loop and angle for each of the five battery readings. 3.Using the averaged data, graph B loop vs. tan .

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Tangent Galvanometer Lab Post Lab 4. From your graph calculate the Earth’s magnetic field. Show your work in the space below Magnetic Declination

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Tangent Galvanometer Lab Post Lab 5. If both of the magnetic fields were the same strength, how many degrees from due north would the compass deflect? Draw a vector diagram indicating the magnetic fields and the direction the compass would deflect.

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Tangent Galvanometer Lab Post Lab 6. An important aspect of the lab was to align your coils in the north-south direction. How would your results differ if you aligned the coils east-west direction?

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Magnetic Domains What’s required to produce a magnetic field? MOVING CHARGES Macro and Micro Scales Definition Domain A microscopic magnetic region composed of a group of atoms whose magnetic fields are aligned in a common direction.

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Magnetic Force on a Charged Particle When a charge is placed in a magnetic field, that charge experiences a magnetic force when two conditions exist: 1.The charge is moving relative to the magnetic field. 2.The charge's velocity has a component perpendicular to the direction of the magnetic field.

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Magnetic Force on a Charged Particle 3 rd Right Hand Rule Using your right hand: 1.Point your index fingers in the direction the magnetic field, B. 2.Point your thumb in the direction of the charge's velocity, v, (recall conventional current). 3.The magnetic force F B is directed out of the palm of your hand.

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Magnetic Force on a Charged Particle 3 rd Right Hand Rule (Optional) Using your right hand: 1.Point your index finger in the direction of the charge's velocity, v, (recall conventional current). 2.Point your middle finger in the direction of the magnetic field, B. 3.Your thumb now points in the direction of the magnetic force, F B.

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Magnetic Force on a Charged Particle 3 rd Right Hand Rule Examples

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Magnetic Field Unit Review the equation for electric field. What’s required to produce a magnetic field. Discuss units of Tesla and Gauss.

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Force on a Charged Particle in B. Equation F B = qv X B = qvBsin Example A proton moves straight upward (away from the ground) through a uniform magnetic field that points east to west and has a magnitude of 2.5 T. If the proton moves with a speed of 1.5 X 10 7 m/s through this field what force (magnitude and direction) will act on it?

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Force on a Charged Particle in B. Example Continued Draw the subsequent path of the charge particle. Calculate the proton’s acceleration. Calculate the radius of its circular path. What’s its period of revolution?

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Force on a Current-Carrying Wire Equation-Derivation F B = BILsin Example The magnetic force on a straight 0.15 m segment of wire carrying a current of 4.5 A is 1.0 N. What is the magnitude of the component of the magnetic field that is perpendicular to the wire?

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Force on a Parallel Wires Relationship Determine the relationship between force and direction of current. Parallel Currents – Attract Anti-Parallel Currents - Repel

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Motors Definition Converts electrical energy into mechanical energy. Let’s analyze the torque produced by the current-carrying armature.

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Commutator Split Ring Maintains unidirectional current flow.

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Commutator Slip Ring Maintains bidirectional current flow.

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Motor Lab PreLab READ THE DIRECTIONS CAREFULLY! THINK BEFORE YOU SAND!

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Motor Lab Post Lab Review sanding of armature

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Generators Definition Converts mechanical energy into electrical energy. Let’s analyze the current produced by a rotating armature in a magnetic field.

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Commutator Split Ring Maintains unidirectional current flow.

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Commutator Slip Ring Maintains bidirectional current flow.

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Induced Currents Two Methods 1.Moving a wire in a stationary magnetic field. 2.Moving (changing) the magnetic field about a stationary wire. Let’s examine the current produced in a closed loop of wire in the presence of a changing magnetic field.

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Transformers Definition A device the changes the potential difference or current. Energy is always Conserved. Energy in equals Energy out Power in equals Power out. Equation derivation.

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Transformers Types of Transformers 1.Step-Up Transformer The secondary voltage is greater than the primary voltage. 2. Step-Down Transformer The primary voltage is greater than the secondary voltage. What’s the current relationship?

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Example A transformer is used to convert 120 V to 9.0 V for use in a portable CD player. If the player needs 360 mA to operate, how much current is being supplied to the transformer? Is this a step-up or step-down transformer?

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Lecture Outline Chapter 19 College Physics, 7 th Edition Wilson / Buffa / Lou © 2010 Pearson Education, Inc.

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