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 Question The picture shows the field lines outside a permanent magnet. The field lines inside the magnet point: 1)Up 2)Down 3)Left to right 4)Right to left 5)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

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