JEE Advance - Physics (2007 - Paper 2 Offline - No. 8)
A magnetic field $$\overrightarrow{\mathrm{B}}=\mathrm{B}_{0} \hat{j}$$ exists in the region $$a < x < 2 a$$ and $$\overrightarrow{\mathrm{B}}=-\mathrm{B}_{0} \hat{j}$$, in the region $$2 a < x < 3 a$$, where $$\mathrm{B}_{0}$$ is a positive constant. A positive point charge moving with a velocity $$\vec{v}=v_{0} \hat{i}$$, where $$v_{0}$$ is a positive constant, enters the magnetic field at $$x=a$$. The trajectory of the charge in this region can be like,
Explanation
For $$a < x < 2 a$$
$$\overrightarrow{\mathrm{B}}=\mathrm{B}_{0} \hat{j} $$
The initial velocity is $$\vec{v}=v \cdot \hat{j}$$
From the above diagram it is clear that force on the particle is toward $$+z$$-axis (by applying Fleming's left hand rule) at $$x=a$$, which shifts the particle as shown in the x-z plane
For $$2 a < x < 3 a$$
$$\overrightarrow{\mathrm{B}}=-\mathrm{B}_{0} \hat{j}$$
The direction of velocity is shown at $$x=2 a$$.
Again by using Fleming's left hand rule, we get direction of force.
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