2. In the circuit shown below, the switch is initially closed and the bulb glows brightly. When the switch is opened, what happens to the brightness of the bulb?

A. The brightness of the bulb is not affected.B. The bulb gets dimmer.C. The bulb gets brighter.D. The bulb initially brightens, then dims.E. The bulb initially dims, then brightens.

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Additional Clicker Questions

2. In the circuit shown below, the switch is initially closed and the bulb glows brightly. When the switch is opened, what happens to the brightness of the bulb?

B. The bulb gets dimmer.

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Answer

Capacitor Concepts

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Key Equations for Circuits – another way to look at loop rule

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• Magnets and the magnetic field

• Electric currents create magnetic fields

• Magnetic fields of wires, loops, and solenoids

• Magnetic forces on charges and currents

• Magnets and magnetic materials

Chapter 24Magnetic Fields and Forces

Topics:

Sample question:This image of a patient’s knee was made with magnetic fields, not x rays. How can we use magnetic fields to visualize the inside of the body?

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3-D Arrows, Cross Products, and Right Hand Rule 1

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• Showing vectors in 3D

• Cross Product

For direction use Right-hand rule 1

• Right-hand rule 1 (RHR 1) => for finding direction of cross-product vector

(Cross-Product Rule)1.Point right hand in the direction of the first vector (vector A)

2.Rotate your right hand until you can point your fingers in the direction of the second vector (vector B)

3.Thumb points in direction the cross-product vector (vector C)

Electric vs. Magnetic Interactions

1. Nature of Magnetic Interactions

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Discovering Magnetism

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The Magnetic Field

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Mapping Out the Field of a Bar Magnet

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Mapping Out the Magnetic Field Using Iron Filings

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Drawing Field Lines of a Bar Magnet

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Magnetic Fields Produced by Bar Magnets

A single bar magnet A single bar magnet(closeup)

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Magnetic Fields Produced by Bar Magnets

Two bar magnets, unlike poles facing

Two bar magnets,like poles facing

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Checking Understanding

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Magnetic Fields from Two MagnetsBar Magnets A and B are placed at right angles. Two compasses, X and Y are placed so that they are equidistant from the two magnets as shown

A.) The arrow in compass X indicates the direction in which the North pole of the compass is pointing. Indicate the North and South ends of both magnets in the diagram

B.) Draw an arrow in compass Y to show the direction in which the North pole of the compass needle would point.

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Magnetic Fields Around Us

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Key Points• Three types of magnetic interactions

1. no interaction with either pole of a magnet => object is non-magnetic

2. attracted to both poles of a magnet => object is magnetic

3. Attracted to one pole and repelled by the other pole=> object is a magnet

• Magnetic field vector from a bar magnet is a super position of the magnetic field vectors from the N and S poles:

• Vector from N pole points away from N pole

• Vector from S pole points towards S pole

• Field lines form complete loops inside and outside of magnet• Field lines outside magnet go from N to S poles

• Field lines inside magnet go from S to N poles

• Magnetic Field vectors at a point are tangential to Magnetic Field Lines

Electric Currents Also Create Magnetic Fields

A long, straight wire

A current loop A solenoid

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The Magnetic Field of a Straight Current-Carrying Wire

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Representing Vectors and Currents That Are Perpendicular to the Page

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Checking Understanding

Point P is 5 cm above the wire as you look straight down at it. In which direction is the magnetic field at P?

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Answer

Point P is 5 cm above the wire as you look straight down at it. In which direction is the magnetic field at P?

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Drawing Field Vectors and Field Lines of a Current-Carrying Wire

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Drawing a Current Loop

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The Magnetic Field of a Current Loop

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The Magnetic Field of a Solenoid

A short solenoid A long solenoid

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The Magnitude of the Field due to a Long, Straight, Current-Carrying Wire

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Checking Understanding

A. 10 A to the right.

B. 5 A to the right.

C. 2.5 A to the right.

D. 10 A to the left.

E. 5 A to the left.

F. 2.5 A to the left.

The magnetic field at point P is zero. What are the magnitude and direction of the current in the lower wire?

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E. 5 A to the left.

The magnetic field at point P is zero. What are the magnitude and direction of the current in the lower wire?

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Answer