WB JEE 2017 | Magnetism Question 28 | Physics

WB JEE 2017

MCQ (Single Correct Answer)

-0.25

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)

0.5 m

0.2 m

0.1 m

0.05 m

WB JEE 2017

MCQ (Single Correct Answer)

-0.5

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

$${{{2m{u^2}} \over {eE}}}$$

$${{{eE} \over {2m{u^2}}}}$$

$${{{mu} \over {2eE}}}$$

$${{{m{u^2}} \over {2eE}}}$$

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