# Homework Help: Find number of turns in the solenoid

1. Nov 2, 2009

### jackxxny

1. The problem statement, all variables and given/known data
I have the following information about the problem.

i have the speed of an electron = v
the diameter of a circular path = d
the length of a solenoid = x
the current that the solenoid carried = I

I need to find the number of turns in the solenoid.
2. Relevant equations

i used the following equations
QvB=v2m/r

B=$$\mu$$NI/l

3. The attempt at a solution

then i put "B" in the first equation and i solve for N. Is that correct?

Last edited: Nov 2, 2009
2. Nov 3, 2009

### rock.freak667

Re: solenoid

Yes, do that.

3. Nov 3, 2009

### jackxxny

Re: solenoid

the only weird thing is that i get a number like

.121

and it is not a turn .121??? or it can be a valid answer?

4. Nov 3, 2009

### rock.freak667

Re: solenoid

no, you can't really get less than one. Post the numbers and your working and we'll see if you went wrong anywhere.

5. Nov 3, 2009

### jackxxny

Re: solenoid

v=1570 m/s
d = 1.57 cm
x = 35 cm
I = 2.61 A
what I did is :
N=(vmx)/(rQI*4*pi*10^-7)

6. Nov 3, 2009

### rock.freak667

Re: solenoid

I get the same answer as you, so I guess you'll need to put what you get and round up and put N=1

7. Nov 3, 2009

### jackxxny

Re: solenoid

the problem really states....

....that the electron follows a circular path of diameter 1.57 cm near the center of an evacuated solenoid of length 35 cm .

does that changes anything?