TOF (mass spectrometer) Analyzer Question

[carlphysics30]

Homework Statement

An unknown hydrocarbon ion required 9.415*10^-6 seconds to travel through the 0.250 T magnetic field of a mass spectrometer with a radius of curvature of 14.1 cm. Since the magnetic chamber is shaped like a 'D' it only travels half way around the circle.

a. find the speed of the ion through the magnetic field
b. identity of the ion using the charge to mass ratio (q/m)[/B]

Homework Equations

Fm = qvB
Fm=Fnet=Fc
qvB=mv^2/r
Fc=(4π^2/T^2)

Unknown variables: q (charge), m (mass), v (velocity) or V (voltage)[/B]

The Attempt at a Solution

a. Rearranging the formula gives me v=qBr/m. I do not have the (q/m) ratio, so that creates two unknown variables. Next, I tried substituting (4π^2/T^2) as an equivalent for qvB. [/B]

The Fm is 4.453680806*10^11 N.

After this step I am stuck.

ANSWER FROM THE BOOK:
The velocity is 4.7*10^4 m/s, and the substance is pentane, with a (q/m) ratio of 1.34*10^6.

 

[mfb]

You can calculate the curve length the ion travels in the spectrometer, and you know the time. That allows to get the speed.
Afterwards you can find q/m.

 

[carlphysics30]

You can calculate the curve length the ion travels in the spectrometer, and you know the time. That allows to get the speed.
Afterwards you can find q/m.

WOW THANKS. I didn't even know it was that simple! thanks again! :)