Question

An electron travelling with a speed u along the positive x-axis enters into a region of magnetic field where B = . It comes out of the region with speed v then –

• A. v = u at y > 0
• B. v = u at y < 0
• C. v> u at y > 0
• D. v > u at y < 0

Answer 1

Answer: (B)

v = u at y < 0

Answer 2

$\overrightarrow { \mathrm { F } } = \mathrm { q } ( \overrightarrow { \mathrm { v } } \times \overrightarrow { \mathrm { B } } )$ = $- e \left( u \hat { i } \times - B _ { 0 } \hat { k } \right)$ = –euB₀ So it will move towards y < 0 and speed remains constant.