Q. In the figure shown, a charge q moving with a velocity v along the x-axis enter into a region of uniform magnetic field. The minimum value of v so that the charge q is able to enter the region x > b

(a) $ \displaystyle \frac{q B b}{m}$

(b) $ \displaystyle \frac{q B a}{m}$

(c) $ \displaystyle \frac{q B( b -a )}{m}$

(d) $ \displaystyle \frac{q B( b +a )}{2m}$

Ans: (c)

Sol: If particle enter the region x > b

Then , R ≥ (b-a)