1
WB JEE 2017
MCQ (Single Correct Answer)
+1
-0.25
Change Language
A proton is moving with a uniform velocity of $${{{10}^6}}$$ ms$$-$$1 along the Y-axis, under the joint action of a magnetic field along Z-axis and an electric field of magnitude 2 $$ \times $$ 104 Vm$$-$$1 along the negative X-axis. If the electric field is switched off, the proton starts moving in a circle. The radius of the circle is nearly (given : $${e \over m}$$ ratio for proton $$ \approx $$ 108 Ckg$$-$$1)
A
0.5 m
B
0.2 m
C
0.1 m
D
0.05 m
2
WB JEE 2017
MCQ (Single Correct Answer)
+2
-0.5
Change Language
A particle with charge e and mass m, moving along the X-axis with a uniform speed u, enters a region where a uniform electric field E is acting along the Y-axis. The particle starts to move in a parabola. Its focal length (neglecting any effect of gravity) is
A
$${{{2m{u^2}} \over {eE}}}$$
B
$${{{eE} \over {2m{u^2}}}}$$
C
$${{{mu} \over {2eE}}}$$
D
$${{{m{u^2}} \over {2eE}}}$$
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