# Eddy Currents

#### carpelumen

1. Homework Statement
A magnet of mass 0.10 kg is dropped from rest and falls vertically through a 35.0 cm copper tube. Eddy currents are induced, causing the copper to warm up. The speed of the magnet as it emerges from the tube is 1.50 m/s. How much heat energy is dissipated to the environment?

2. Homework Equations
E = mgh

3. The Attempt at a Solution
h = 35 cm --> .35 m

E = (.10 kg) * (9.81) * (.35 m) = .3433 J

Is the equation incorrect?

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#### ehild

Homework Helper
1. Homework Statement
A magnet of mass 0.10 kg is dropped from rest and falls vertically through a 35.0 cm copper tube. Eddy currents are induced, causing the copper to warm up. The speed of the magnet as it emerges from the tube is 1.50 m/s. How much heat energy is dissipated to the environment?

2. Homework Equations
E = mgh

3. The Attempt at a Solution
h = 35 cm --> .35 m

E = (.10 kg) * (9.81) * (.35 m) = .3433 J

Is the equation incorrect?
It is the initial energy if you take the potential energy zero at the bottom of the tube. But what is the loss of energy?

ehild

#### NascentOxygen

Mentor
1. Homework Statement
A magnet of mass 0.10 kg is dropped from rest and falls vertically through a 35.0 cm copper tube. Eddy currents are induced, causing the copper to warm up. The speed of the magnet as it emerges from the tube is 1.50 m/s. How much heat energy is dissipated to the environment?

2. Homework Equations
E = mgh

3. The Attempt at a Solution
h = 35 cm --> .35 m

E = (.10 kg) * (9.81) * (.35 m) = .3433 J

Is the equation incorrect?
What happens to the P.E. that you have just calculated the magnet loses?

#### Jakob Weg

An illustrative experiment on this issue

#### rude man

Homework Helper
Gold Member
An illustrative experiment on this issue
Good! We note that a larger-diameter tube slows the magnet down more than a smaller-diameter one, following emf = -dΦ/dt. Also that Cu slowed the magnet down more than did Al or brass, following i = emf/R. Vielen Dank!

#### rude man

Homework Helper
Gold Member
1. Homework Statement
A magnet of mass 0.10 kg is dropped from rest and falls vertically through a 35.0 cm copper tube. Eddy currents are induced, causing the copper to warm up. The speed of the magnet as it emerges from the tube is 1.50 m/s. How much heat energy is dissipated to the environment?

2. Homework Equations
E = mgh

3. The Attempt at a Solution
h = 35 cm --> .35 m

E = (.10 kg) * (9.81) * (.35 m) = .3433 J

Is the equation incorrect?
That's the kinetic energy (k.e.) that would have developed in the absence of the copper tube. What was the k.e. with the tube?

"Eddy Currents"

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