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An electron is accelerated from rest through potential difference V and then enters a region of uniform magnetic field, where it undergoes uniform circular motion. The figure gives the radius r of that motion versus V1/2. The vertical axis scale is set by Is= 4.50 mm, and the horizontal axis scale is set by V,1/2= 26.5 V1/2. What is the magnitude of the magnetic field? r (mm) 0 Vi/2 Vi/2 (V1/2) Number i Units