# Electromagnet help please?

1. Aug 30, 2006

### NUMB_NUTS

:surprised
HI EVEYONE,
NEED TO TAALK TO SOMEONE WHO IS UP ON CALCULATING THE VALUE OF (B), REQUIRED TO LIFT A PLATE OF XXNEWTONS. ALSO ESTIMATE THE M.M.F REQUIREDTO LIFT THE SAME PLATE.
THANKS

2. Aug 30, 2006

### Staff: Mentor

No need to yell. What are the equations that describe the force generated by current flowing in a coil?

3. Aug 30, 2006

### NUMB_NUTS

I WILL TRY EXPLAIN MY QUESTION AND PRESENT YOU WITH ALL THE FACTS I HAVE AT MY DISPOSAL.
In the question it is first mentioned that the pull,P, exerted at each pole of the magnet is given by the equation:
P = Bsquared x A divided by 2 x permeability of free space.
A being CSA of the pole faces
free space being 4 x pie x 10 to power of -7.

OK.
next we have c.s.a of magnet: 22 x 22 cm.
angle in degrees: 120.
relative permeability of magnet: 2000.
relative permeability of plate: 1000.
thickness of plate: 5cm
weight of plate: 10'000 Newtons.

I have drawn out a diagram to show you what the radius and angle are all about. Can i paste a paint document here? It would help a lot.
Many thanks .

4. Aug 30, 2006

### LM741

just save the the jpeg file on your computer and then attach it to the post.

5. Aug 31, 2006

### NUMB_NUTS

electromagnet problem, need help please!

View attachment electromagnet question.doc

Q1, I need to calculate the value of B required to lift a plate.
Q2, Estimate the mmf F required to lift the same plate.

I understand P = B squared x A. divided by 2 x permeability of free space.

This is what I have to work with:

The plate to be lifted weighs, 10000 Newtons
Relative permeability of plate, 1000
Thickness of plate, 5 cm.

c.s.a. of magnet, 22 x 22 cm.
radius (mean) of magnet, 0.5m ( shown as red circle)
angle in degrees, 120.

I am assuming you have to first calculate the distance between the 2 poles. Using the cosine rule I make it: 0.75metres.

Now I need help with the rest please.
I donâ€™t just want the answer I want to understand the formula properly.

Many thanks.

6. Sep 3, 2006

### Ouabache

Can you define more clearly, the units for each of the variables in your expression
$$P = \frac{B^2 A}{2 \mu_o}$$

by the way, your expression looks similar to one I note on this page. Are you using the same units?

From your given information, I don't see a value for "magnetic flux density" B. Perhaps you have some given information from which you can derive B.

Last edited: Sep 4, 2006