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- 2. What is the shape of the trajectory that a charged particle follows in a uniform magnetic field?
- Helix
- Parabola
- Circle
- Ellipse
- Hyperbola

- What is the SI unit for the strength of the magnetic field?
- Gauss
- Henry
- Tesla
- Becquerel
- Bohr magneton

- 4. The magnetic field of a straight, current-carrying wire is
- parallel to the wire.
- inside the wire.
- perpendicular to the wire.
- around the wire.
- zero.

- 3. The magnetic field of a point charge is given by
- Biot-Savart’s law.
- Faraday’s law.
- Gauss’s law.
- Ampère’s law.
- Einstein’s law.

What is the SI unit for the strength of the magnetic field?

- Gauss
- Henry
- Tesla
- Becquerel
- Bohr magneton

What is the shape of the trajectory that a charged particle follows in a uniform magnetic field?

- Helix
- Parabola
- Circle
- Ellipse
- Hyperbola

The magnetic field of a point charge is given by

- Biot-Savart’s law.
- Faraday’s law.
- Gauss’s law.
- Ampère’s law.
- Einstein’s law.

The magnetic field of a straight, current-carrying wire is

- parallel to the wire.
- inside the wire.
- perpendicular to the wire.
- around the wire.
- zero.

Field Around Magnet

- Use a compass to map the direction of the magnetic field surrounding a magnet.
- White board your results. In particular:
- how does the strength of the field vary with distance from the wire?
- how does the field direction relate to the poles of the magnet?

Magnetism

Activity: Map Field of Magnets

- Use iron filings to map the field of a
- bar magnet
- horseshoe magnet

- White board results
- draw field lines.
- how might magnets generate magnetic fields?

Magnetism

Magnetic Field Lines

- direction of magnetic field, B, is parallel to field line
- number of lines per area is proportional to strength of field

- field lines point
- from N to S
- field lines formclosed loops

Magnetism

Magnets are similar to Electric Dipoles

Magnetism

Ferromagnetism

- Ferromagnetic material
- iron or other materials that can be made into magnets

- You can make a magnet from iron by placing it in a strong B field
- individual domains become aligned with external B field

- Loss of magnetism from:
- dropping
- heating
- Curie temperature
- 1043 K for iron

- Curie temperature

Preferentially

downwards

Random

Magnetism

Cross Product – Right Hand Rule

Magnetism

Force on a moving charge

- Right Hand Rule (#2)
- qv = fingers
- B = bend fingers
- F = thumb

- Find the direction of the force on a negative charge for each diagram shown.

Magnetism

Think-Pair-Share

- Derive an expression for the radius of an e-’s orbit in a uniform B field. Express your answer in terms of me, v, qe, and B. Turn in your solution!

Magnetism

Earth’s Magnetic Field

- magnetic declination
- angular difference between geographic north and magnetic north
- varies with latitude

Magnetism

The Source of the Magnetic Field: Moving Charges

The magnetic field of a charged particle q moving with velocity v is given by the Biot-Savart law:

where r is the distance from the charge and θ is the angle between v and r.

The Biot-Savart law can be written in terms of the cross product as

The Magnetic Field of a Current

The magnetic field of a long, straight wire carrying current I, at a distance d from the wire is

The magnetic field at the center of a coil of N turns and radius R, carrying a current I is

Magnetic Dipoles loop

The magnetic dipole moment of a current loop enclosing an area A is defined as

The SI units of the magnetic dipole moment are A m2. The on-axis field of a magnetic dipole is

EXAMPLE 33.7 The field of a magnetic dipole loop

QUESTIONS:

Ampère’s law loop

Whenever total current Ithrough passes through an area bounded by a closed curve, the line integral of the magnetic field around the curve is given by Ampère’s law:

The strength of the uniform magnetic field inside a solenoid is

where n = N/l is the number of turns per unit length.

The Magnetic Force on a Moving Charge is

The magnetic force on a charge q as it moves through a magnetic field B with velocity v is

where α is the angle between v and B.

Magnetic Forces on Current-Carrying Wires is

Consider a segment of wire of length l carrying current I in the direction of the vector l. The wire exists in a constant magnetic field B. The magnetic force on the wire is

where α is the angle between the direction of the current and the magnetic field.

EXAMPLE 33.13 Magnetic Levitation is

QUESTION:

Applications is

Applications is

Applications is

Does the compass needle rotate clockwise (cw), counterclockwise (ccw) or not at all?

- Clockwise
- Counterclockwise
- Not at all

Does the compass needle rotate clockwise (cw), counterclockwise (ccw) or not at all?

- Clockwise
- Counterclockwise
- Not at all

The magnetic field at the position P points counterclockwise (ccw) or not at all?

- Into the page.
- Up.
- Down.
- Out of the page.

The magnetic field at the position P points counterclockwise (ccw) or not at all?

- Into the page.
- Up.
- Down.
- Out of the page.

The positive charge is moving straight out of the page. What is the direction of the magnetic field at the position of the dot?

- Left
- Right
- Down
- Up

The positive charge is moving straight out of the page. What is the direction of the magnetic field at the position of the dot?

- Left
- Right
- Down
- Up

What is the current direction in this loop? And which side of the loop is the north pole?

- Current counterclockwise, north pole on bottom
- Current clockwise; north pole on bottom
- Current counterclockwise, north pole on top
- Current clockwise; north pole on top

What is the current direction in this loop? And which side of the loop is the north pole?

- Current counterclockwise, north pole on bottom
- Current clockwise; north pole on bottom
- Current counterclockwise, north pole on top
- Current clockwise; north pole on top

An electron moves perpendicular to a magnetic field. What is the direction of ?

- Left
- Into the page
- Out of the page
- Up
- Down

An electron moves perpendicular to a magnetic field. What is the direction of ?

- Left
- Into the page
- Out of the page
- Up
- Down

What is the current direction in the loop? the direction

- Out of the page at the top of the loop, into the page at the bottom.
- Out of the page at the bottom of the loop, into the page at the top.

What is the current direction in the loop? the direction

- Out of the page at the top of the loop, into the page at the bottom.
- Out of the page at the bottom of the loop, into the page at the top.

Which magnet or magnets produced this induced magnetic dipole?

- a or d
- a or c
- b or d
- b or c
- any of a, b, c or d

Which magnet or magnets produced this induced magnetic dipole?

- a or d
- a or c
- b or d
- b or c
- any of a, b, c or d

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