Lesson 6

Lenz’s LawLiceo Alfano

Reminder

• Last time:

• Currents create magnetic fields, and are affected by magnetic fields

• Electric motors spin due to the forces from the magnetic field

• We can make an electromagnet by wrapping a wire around a conductor

Magnetic Fields and Current

• We know that a magnetic field will create a force on a current

• We know that a current will create a magnetic field

• Now, we look at one more relationship between currents and magnetic fields

• Magnets through 3 pipes video

• Magnet through ring animation

What’s Going On?

• When a conductor feels a changing magnetic field, it induces (creates) a current inside the conductor

• What does a current create?

• Lenz’s Law tells us that the current will be created in the direction that opposes the change in the magnetic field – it wants to keep the magnetic field constant

Lenz’s Law Example• Magnetic field through a ring: as the magnet gets

closer, does the field get stronger or weaker?

• The ring doesn’t want this change – it creates a current to try to keep the field constant, so which way will the current go?

Videos

• Lenz’s law explanation video

• Lenz’s law animation

• Ring around a rod video

• Coil of copper over aluminum plate video

• Coins falling by magnets video

Concept Question

The magnetic field shown through the circle of wire is increasing with time. The induced current will be

1)Clockwise

2)Counterclockwise

Concept Question

The magnetic field shown through the circle of wire is increasing with time. The induced current will be

1)Clockwise

2)Counterclockwise

Concept Question

The magnetic field shown through the circle of wire is decreasing with time. The induced current will be

1)Clockwise

2)Counterclockwise

Concept Question

The magnetic field shown through the circle of wire is decreasing with time. The induced current will be

1)Clockwise

2)Counterclockwise

Concept Question

A square loop falls through a magnetic field as shown. The induced current will be

1)Clockwise

2)Counterclockwise

Concept Question

A square loop falls through a magnetic field as shown. The induced current will be

1)Clockwise

2)Counterclockwise

Concept Question

A loop of blue wire is inside a circuit. When the current is turned on, which way will the current in the blue wire go?

1)Clockwise

2)Counterclockwise

Concept Question

A loop of blue wire is inside a circuit. When the current is turned on, which way will the current in the blue wire go?

1)Clockwise

2)Counterclockwise