Question

If an electron enters with a velocity into a cubical region in a uniform electromagnetic field and the orbit of the electron is found to spiral down inside the cube in plane parallel to the x-y plane then the configuration of electric field and magnetic field is

• A.
• B. $\vec { E } = E _ { 0 } \hat { i } , \vec { B } = B _ { 0 } \hat { k }$
• C.
• D.

Answer 1

Answer: (B)

$\vec { E } = E _ { 0 } \hat { i } , \vec { B } = B _ { 0 } \hat { k }$

Answer 2

The orbit of the electron spirals down inside the cube in a plane parallel to x-y plane. therefore must be along +z direction and should be along x-axis

i.e. $\overrightarrow { \mathrm { B } } = \mathrm { B } _ { 0 } \hat { \mathrm { K } }$ and $\overrightarrow { \mathrm { E } } = \mathrm { E } _ { 0 } \hat { \mathrm { i } }$ where $\mathrm { E } _ { 0 } > 0$