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

Question

A proton moving with a constant velocity passes through a region of space without any change in its velocity. If

\overset{\to}{E}

and

\overset{\to}{B}

represent the electric and magnetic fields respectively, then the region of space may have :
(A)

E = 0, B = 0

; (B)

E = 0, B \ne 0

; (C)

E \ne 0, B = 0

; (D)

E \ne 0, B \ne 0

Quantrex Academy · Accepted Answer

Correct answer: C. (A), (B) and (D) only

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

$\overset{\to}{F}e + \overset{\to}{F}m = q\overset{\to}{E} + q\left(\overset{\to}{v} \times \overset{\to}{B}\right) . . . \left(1\right)$

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

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

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

A proton moving with a constant velocity passes through a region of...

Options

Correct answer

Step-by-step solution

More from Magnetic Effects of Current