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Physics Chapter 12 : Topic 7
Velocity Selector
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Velocity selection is the process of:
Reasoning: Velocity selection allows only particles moving with a particular velocity to pass through the system.
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Velocity selectors work on the principle of balancing:
Reasoning: In a velocity selector, electric and magnetic forces act in opposite directions and balance each other.
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In a velocity selector, a charged particle experiences electric force due to:
Reasoning: The electric field exerts a force $\mathbf{F = qE}$ on the charged particle.
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The magnetic force on a moving charged particle is given by:
Reasoning: Magnetic force depends on magnetic field, charge, velocity, and angle between velocity and field.
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In a velocity selector, the electric and magnetic forces are:
Reasoning: The two forces cancel for particles with the selected velocity.
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For a particle to pass straight through a velocity selector, the condition is:
Reasoning: Straight-line motion occurs when electric force equals magnetic force.
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The velocity selected by a velocity selector is:
Reasoning: From $\mathbf{qE = Bqv}$, cancelling $\mathbf{(q)}$ gives $\mathbf{v = E\ /\ B}$.
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In a velocity selector, the magnetic field is arranged:
Reasoning: Electric and magnetic forces must act in opposite directions, requiring perpendicular fields.
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A charged particle moving through a velocity selector faster than the selected velocity will:
Reasoning: For higher velocity, magnetic force becomes greater than electric force.
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A particle moving slower than the selected velocity in a velocity selector will:
Reasoning: Magnetic force decreases with velocity, so electric force dominates for slower particles.
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The charge of a particle does not affect its selected velocity because:
Reasoning: Both electric and magnetic forces contain charge $\mathbf{q}$, which cancels.
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In a velocity selector, a neutral particle:
Reasoning: Neutral particles have no charge, so electric and magnetic forces do not act.
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A velocity selector can separate particles based on their:
Reasoning: Only particles with the correct velocity experience balanced forces.
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If the electric field strength is increased while magnetic field remains constant, the selected velocity:
Reasoning: Since $\mathbf{v = E\ /\ B}$, increasing $\mathbf{E}$ increases selected velocity.
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If the magnetic field strength is increased while electric field remains constant, the selected velocity:
Reasoning: Velocity is inversely proportional to magnetic field strength.
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A velocity selector allows particles to pass straight because:
Reasoning: Equal and opposite electric and magnetic forces produce zero net force.
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A particle enters a velocity selector with velocity greater than $\mathbf{E\ /\ B}$. The magnetic force is:
Reasoning: Magnetic force increases with velocity, so faster particles experience greater magnetic force.
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A particle enters a velocity selector with velocity less than $\mathbf{E\ /\ B}$. The particle will be:
Reasoning: At lower velocities, magnetic force is smaller, so electric force causes deflection.
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In a velocity selector, the direction of electric force depends on:
Reasoning: Electric force direction depends on whether the charge is positive or negative.
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The direction of magnetic force depends on:
Reasoning: Magnetic force direction depends on charge type and the directions of velocity and magnetic field.
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A velocity selector is commonly used in:
Reasoning: Velocity selectors are used to select particles with known velocities before analysis.
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A particle with charge $\mathbf{(q)}$ enters a velocity selector. The electric force is:
Reasoning: Electric force on a charge in an electric field is $\mathbf{F = qE}$.
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A particle moving perpendicular to a magnetic field experiences maximum magnetic force because:
Reasoning: Magnetic force is maximum when velocity is perpendicular to the field.
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If the magnetic field in a velocity selector is removed, the particle:
Reasoning: Without magnetic force, only electric force acts and deflects the particle.
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If the electric field in a velocity selector is removed, the particle:
Reasoning: Without electric force, magnetic force causes deflection.
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A velocity selector does not depend on:
Reasoning: Charge cancels out in the equation $\mathbf{v = E\ /\ B}$.
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If $\mathbf{E = 6000\ N/C}$ and $\mathbf{B = 2\ T}$, the selected velocity is:
Reasoning: $\mathbf{v = E\ /\ B = 6000\ /\ 2 = 3000\ m/s}$
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A velocity selector selects particles because:
Reasoning: Only particles with $\mathbf{v = E\ /\ B}$ experience zero net force.
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If two particles with different masses but the same velocity enter a velocity selector:
Reasoning: Selection depends on velocity, not mass.
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The main purpose of combining electric and magnetic fields in a velocity selector is to:
Reasoning: Opposing electric and magnetic forces select particles with a specific velocity.
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