A) remains constant
B) increases
C) decreases
D) becomes zero
Correct Answer: A
Solution :
Key Idea: Force due to magnetic field provides the required centripetal force. The force due to magnetic field \[B\] is \[F=qvB\sin \theta \] ... (i) When particle with charge\[q\]enters perpendicularly then\[\theta ={{90}^{o}}\], so\[F=qvB\]and required centripetal force is \[F=\frac{m{{v}^{2}}}{r}\] ... (ii) From Eqs. (i)-and (ii), we get \[\frac{m{{v}^{2}}}{r}=qvB\] \[\Rightarrow \] \[v=\frac{qrB}{m}\] Kinetic energy\[K=\frac{1}{2}m{{v}^{2}}=\frac{1}{2}m{{\left( \frac{qrB}{m} \right)}^{2}}\] \[=\frac{{{q}^{2}}{{r}^{2}}{{B}^{2}}}{2m}=\]constant Hence, kinetic energy remains constant.You need to login to perform this action.
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