This magnet question confounds me

[lodovico]

Homework Statement

Today, my teacher gave us some practice AP multiple choice and my friend and I were debating between answer choices H and J (changed from A and B to remove any confusion) the question as i remember it:
blah blah... B-field into the page, constant velocity v, radius R and charge q. which graph shows the relationship between B-field and radius.. something with radius getting smaller as B-field gets larger

Choice H: this is a straight line coming from +y crossing the +x axis (basically a straight negative slope)

Choice J: the (1/x) graph with x>0

Homework Equations

Fc = mv^2/r
Fb= qvB

The Attempt at a Solution

Fc=Fb
\frac{mv^2}{r}=qvB
\frac{mv}{r}=qB
since mv and q are constants, is it ok to treat them as 1? that is what i did so...

\frac{1}{r}=B
\frac{1}{B}=r

since on the graphs r was the y-axis and B was the x-axis

i chose the (1/x) shaped graph

 

[berkeman]

Homework Statement

Today, my teacher gave us some practice AP multiple choice and my friend and I were debating between answer choices H and J (changed from A and B to remove any confusion) the question as i remember it:
blah blah... B-field into the page, constant velocity v, radius R and charge q. which graph shows the relationship between B-field and radius.. something with radius getting smaller as B-field gets larger

Choice H: this is a straight line coming from +y crossing the +x axis (basically a straight negative slope)

Choice J: the (1/x) graph with x>0

Homework Equations

Fc = mv^2/r
Fb= qvB

The Attempt at a Solution

Fc=Fb
\frac{mv^2}{r}=qvB
\frac{mv}{r}=qB
since mv and q are constants, is it ok to treat them as 1? that is what i did so...

\frac{1}{r}=B
\frac{1}{B}=r

since on the graphs r was the y-axis and B was the x-axis

i chose the (1/x) shaped graph

Yes, it is known as the Lamor Radius:

http://www-fusion.ciemat.es/fusionwiki/index.php/Larmor_radius