A proton moving with a constant velocity passes through a region of space without any change in its velocity. If $\vec{E}$ and $\vec{B}$ represent the electric and magnetic fields respectively, then the region of space may have :
(A) $E = 0, B = 0$ ; (B) $E = 0, B \neq 0$ ; (C) $E \neq 0, B = 0$ ; (D) $E \neq 0, B \neq 0$

Question

Choose the most appropriate answer from the options given below :

TestHub · Accepted Answer

Net force on proton inside an electric and a magnetic field is given by

${\vec{F}}_{e} + {\vec{F}}_{m} = q \vec{E} + q (\vec{v} \times \vec{B}) . . . (1)$

If both $\vec{E}$ and $\vec{B}$ are zero, then ${\vec{F}}_{e}$ and ${\vec{F}}_{m}$ both are zero. Hence, velocity may remain constant. Therefore, option (A) is correct.

If $E = 0, B \neq 0$ , but velocity is parallel or antiparallel to the magnetic field, then also ${\vec{F}}_{e}$ and ${\vec{F}}_{m}$ both are zero. Hence, option (B) is also correct.

If $E \neq 0, B \neq 0$ , but ${\vec{F}}_{e} + {\vec{F}}_{m} = 0$ , then also velocity may remain constant. Thus, option (D) is also correct.

Physics - Magnetism Question with Solution | TestHub

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