# Magnetic field diagram

1. Oct 12, 2009

### Suy

1. The problem statement, all variables and given/known data
http://img19.imageshack.us/img19/3505/picture1ul.jpg [Broken]
Three particles have identical charges and masses. They enter a constant magnetic field and follow the paths shown in the drawing. Rank the speeds of the particles, largest to smallest

2. Relevant equations
r=(mv)/(qB)

3. The attempt at a solution
the book give me 2-3-1, but isn't that the larger the radius , the faster the particles is?
can someone explain it?
ty

Last edited by a moderator: May 4, 2017
2. Oct 12, 2009

### Suy

i guess 2-3-1 is wrong, because they are assuming that 1,2,3 radius is same,
if radius same F=qBv or F=(mv^2)/r, 1 have the lowest magnetic downward force or centripetal force, so if low force, less velocity, this is why 1 will be the slowest.
But if they all have the same force, using this r=(mv)/(qB), (large radius, great speed),because in the diagram they have different radius, so we can't assume they are the same, we can only assume that the force is same, so it would 1>3>2
am i right?

3. Oct 12, 2009

### ideasrule

No, I'm afraid you're talking nonsense. As the question stated, the only thing that's constant for all 3 particles is the magnetic field strength, or B. The particles experience different forces because they trace out circles of different radii, and F=mv^2/r.

2-3-1 is wrong; the actual answer should be 1-3-2. As the OP noted, the faster the speed, the larger the radius.

4. Oct 12, 2009

### Suy

o , i mean the book give me 2-3-1, i was just wondering why the answer is 2-3-1
the book also stated that "Great Force ,Great velocity"

5. Oct 12, 2009

### ideasrule

But 2-3-1 is NOT correct. The answer should be 1-3-2.

6. Oct 12, 2009

### Suy

http://img132.imageshack.us/img132/9773/81045485.jpg [Broken]
Can you tell me if this is right?
1) B
3)C<B<A
For the first one, my friend said it's A,because it bends more,
i think he is wrong...
If i am wrong, plz explain it
ty!

Last edited by a moderator: May 4, 2017
7. Oct 12, 2009

### Suy

anyone?, i need someone to confirm my answer...
TY!