week 1 introduction to magnetism liceo alfano. what is a magnet? applet a magnet is any piece of...
TRANSCRIPT
Week 1
Introduction to Magnetism
Liceo Alfano
What is a Magnet?
• Applet
• A magnet is any piece of material that will attract iron
• Imagine living hundreds of years ago and discovering that certain materials can manipulate objects without touching them. How strange would that be?
What is Magnetism?• Magnetism is a force that exists naturally,
like gravity
• Have you ever played with two magnets to see how they react to one another? What happened?
• Like poles repel, opposite poles attract
What is Magnetism?
• What happens if you cut a magnet in half? Does it make a magnet with only one pole?
• No! It just makes two smaller magnets
• It is impossible to have a magnet with just one pole
• How could you make a really small magnet?
Experiments
• Magnetic field of a permanent bar magnet
• Compass’s reaction to being in the magnetic field
• Exploring magnetic fields worksheet
Magnetic Field of a Bar Magnet
• A magnet has two poles, N and S
• Magnetic field lines start from N and go to S
• Magnets in Motion
Concept QuestionThe picture shows the field lines outside a permanent magnet. The field lines inside the magnet point:
1) Up2) Down3) Left to right4) Right to left5) The field inside is
zero
Concept Question
1) Up
Magnetic field lines are continuous.There are no magnetic charges (monopoles) so B field lines never begin or end
How Does a Compass Work?
• Based on our experiment and the map of a bar magnet’s magnetic field, how does a compass work in a magnetic field?
• A compass always points north on Earth. What does this mean about Earth?
Earth’s Magnetic Field
• Our planet is a huge magnet!
• Compasses always align to point approximately north (but not exactly north, why not?)
Other Magnetic Field Geometries
Other Magnetic Field Geometries
Reminder: Electric Fields
• What kind of particle causes an electric field?
• Any positively or negatively charged particle
• What kind of particles can “feel” electric field?
• Any positively or negatively charged particle
Now: Magnetic Fields
• We will talk about what particles can cause a magnetic field later
• Any moving positively or negatively charged particle can “feel” a magnetic field
• How is a magnetic field different from an electric field?
Magnetic Field Force• Force of a magnetic field on a moving particle:
• F = q v x B
• F is the force on the particle (Newtons)
• q is the charge of the particle (Coulombs)
• v is the velocity of the particle (m/s)
• B is the strength of the magnetic field (Teslas)
Cross Product• In the equation F = q v x B, v x B is a
cross product
• Cross product means the magnetic force is perpendicular to both the velocity of the charge, v, and the magnetic field, B
Direction of Magnetic Force
• Right hand rule = USE YOUR RIGHT HAND – works for small positive charges
• Thumb in the direction particle is moving
• Other fingers in the direction of the magnetic field
• Force comes straight out of your palm
Practice Question
• What direction is the force on a positive charge when entering a uniform B field in the direction indicated?
A) Up
B) Down
C) Left
D) Right
E) Into page
F) Out of page
Practice Question
• What direction is the force on a positive charge when entering a uniform B field in the direction indicated?
A) Up
B) Down
C) Left
D) Right
E) Into page
F) Out of page
Practice Question
• What direction is the force on a positive charge when entering a uniform B field in the direction indicated?
A) Up
B) Down
C) Left
D) Right
E) Into page
F) Out of page
Practice Question
• A particle with a positive charge of 0.001C is moving perpendicular to a magnetic field of strength 0.3T. The particle has a speed of 400 m/s. Calculate the magnitude of the magnetic force exerted on the particle
• The particle is moving to the right and the magnetic field points into the page. Find the direction of the force on the particle
Practice Question
• A particle with a positive charge of 0.001C is moving parallel to a magnetic field of strength 0.3T. The particle has a speed of 400 m/s. Calculate the magnitude of the magnetic force exerted on the particle