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Physics · 2023 · 2 marks
CBSE 2023 · Region 4 · Set 3 · Q23
A particle of charge q and mass m starts moving with uniform velocity v_0 i. Specify the direction of magnetic field which should be set up in the…
A particle of charge $\displaystyle q$ and mass $\displaystyle m$ starts moving with uniform velocity $\displaystyle \mathrm{v}_{0} \hat{\mathrm{i}}$. Specify the direction of magnetic field which should be set up in the region so that the particle moves (a) straight undeviated, and (b) in a circle. Justify your answers.
Marking-scheme solution
Specification of the direction of magnetic field for particle to move
(a)
For straight undeviated path, magnetic field should be set up parallel or antiparallel to velocity vector
\[\vec{F}=q(\vec{\mathrm{v}} \times \vec{B})
\]
Altrenatively: angle between \(\displaystyle \vec{\mathrm{v}}\) and \(\displaystyle \vec{B}, \theta=0^{\circ}\), or \(\displaystyle \theta=180^{\circ}\)
\[\theta=0^{\circ}, \text { or } \theta=180^{\circ}
\]
(b)
If charge particle moves in circle magnetic field should be setup perpendicular to the velocity vector.
\[\vec{F}=q(\vec{\mathrm{v}} \times \vec{B}) \quad \vec{\mathrm{v}} \perp \vec{B}
\]
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