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Physics Chapter 12 : Topic 6
Charged Particle Motion in a Magnetic Field
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A charged particle moving perpendicular to a uniform magnetic field experiences:
Reasoning: Magnetic force acts perpendicular to both velocity and magnetic field.
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When a charged particle enters a uniform magnetic field at $\mathbf{90}^{\mathbf{o}}$ to the field direction, its path becomes:
Reasoning: The magnetic force provides the centripetal force required for circular motion.
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The magnetic force on a moving charged particle does not change its:
Reasoning: Magnetic force is perpendicular to velocity and does no work, so speed remains constant.
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A charged particle moves in a circular path inside a uniform magnetic field because:
Reasoning: The magnetic force continuously changes the direction of motion and acts toward the centre of the circle.
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The direction of magnetic force on a positive charge moving in a magnetic field is determined by:
Reasoning: Fleming’s left-hand rule gives the direction of force on moving positive charges.
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If the charge of a particle moving in a magnetic field is reversed, the direction of circular motion:
Reasoning: Reversing charge reverses the direction of magnetic force.
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A charged particle moving perpendicular to a magnetic field experiences a force that is:
Reasoning: Magnetic force is always perpendicular to the velocity of the moving charge.
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The work done by a magnetic field on a moving charged particle is:
Reasoning: Magnetic force is perpendicular to displacement, so it does no work.
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A charged particle moving in a uniform magnetic field maintains constant:
Reasoning: The magnetic force changes only the direction of velocity, not its magnitude.
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The circular motion of a charged particle in a magnetic field is due to:
Reasoning: Magnetic force provides the inward centripetal force.
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The radius of the circular path of a charged particle moving in a magnetic field is given by:
Reasoning: From centripetal force and magnetic force equality, $\mathbf{r = mv\ /\ Bq}$.
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If the velocity of a charged particle is increased, its circular path radius:
Reasoning: Radius is directly proportional to velocity $\mathbf{(r}\mathbf{\propto}\mathbf{v)}$.
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If magnetic field strength is increased, the radius of the circular path:
Reasoning: Radius is inversely proportional to magnetic field strength $\mathbf{(r}\mathbf{\propto}\mathbf{1/B)}$.
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A charged particle moving in a uniform magnetic field has constant speed because:
Reasoning: The magnetic force is perpendicular to motion and cannot change kinetic energy.
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The acceleration of a charged particle moving in a circular path is:
Reasoning: Circular motion requires centripetal acceleration directed toward the centre.
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A charged particle moving perpendicular to a magnetic field completes one circular revolution. During this motion:
Reasoning: Magnetic field does not perform work, so kinetic energy remains unchanged.
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The time period of circular motion of a charged particle in a uniform magnetic field depends on:
Reasoning: Time period depends on mass, charge, and magnetic field:$\mathbf{T = 2\pi m\ /\ qB}$
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If the mass of a charged particle is increased while charge and magnetic field remain constant, the radius:
Reasoning: Radius is directly proportional to mass.
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An electron and a proton enter the same magnetic field with the same velocity perpendicular to the field. Which has a smaller circular radius?
Reasoning: Electron has much smaller mass, so its radius is smaller.
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A positively charged particle moves in a circular path clockwise. If the charge becomes negative, the path will:
Reasoning: A negative charge experiences force in the opposite direction.
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A particle moving in a magnetic field has its velocity perpendicular to the field. The magnetic force is:
Reasoning: For $\mathbf{\theta =}\mathbf{90}^{\mathbf{o}}$, $\mathbf{sin\ \theta = 1}$ $\Longrightarrow$ So, $\mathbf{F = Bqv}$
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If the velocity of a charged particle becomes zero inside a magnetic field, the magnetic force becomes:
Reasoning: Magnetic force depends on velocity; without motion there is no force.
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The path of a charged particle moving perpendicular to a uniform magnetic field is:
Reasoning: Magnetic force causes circular motion while speed remains constant.
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A charged particle enters a uniform magnetic field. If the particle’s speed remains constant, this indicates that:
Reasoning: Perpendicular force changes direction but not speed.
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The magnetic force on a moving charged particle depends on:
Reasoning: Force is given by $\mathbf{F = Bqv\ sin\ \theta}$.
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A charged particle moving in a magnetic field completes a circle because:
Reasoning: The magnetic force always remains perpendicular to velocity and changes direction continuously.
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The frequency of revolution of a charged particle in a magnetic field depends on:
Reasoning: Cyclotron frequency depends on $\mathbf{qB\ /\ m}$.
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If the magnetic field is doubled, the frequency of circular motion:
Reasoning: Frequency is directly proportional to magnetic field strength.
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A charged particle moving in a magnetic field has centripetal acceleration because:
Reasoning: Magnetic force provides the centripetal force required for circular motion.
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A charged particle moving perpendicular to a magnetic field cannot increase its kinetic energy because:
Reasoning: Since force is perpendicular to displacement, work done is zero and kinetic energy remains constant.
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