In the equation F = BQv for the force on a moving charge, what does B represent and what is its unit?

B represents magnetic flux density, measured in tesla (T).

In the equation F = BQv, what does Q represent and what is its unit?

Q represents the charge of the particle, measured in coulombs (C).

State the formula for the force on a charged particle moving in a magnetic field.

F = BQv, where B is magnetic flux density, Q is charge, and v is velocity.

Calculate the magnetic force when magnetic flux density = 1.09 T, charge = 1.60 × 10⁻¹⁹ C, velocity = 1.12 × 10⁶ m s⁻¹.

Magnetic force = 1.09 × 1.60 × 10⁻¹⁹ × 1.12 × 10⁶ = 1.95 × 10⁻¹³ N.

Under what condition regarding the angle between velocity and field does the formula F = BQv apply?

The formula applies only when the magnetic field is perpendicular to the velocity of the charged particle.

When using Fleming's left-hand rule for a positive charge in a magnetic field, what does the thumb represent?

The thumb represents the direction of the force on the charged particle.

AQA A-Level Physics 7408

Measurements and Their Errors

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Particles and Radiation

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Fields and Their Consequences

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Fields and Their Consequences

Moving charges in a magnetic field

5 things to know
Papers 2 and 3

Overview

F = BQv, circular motion in a field, and the cyclotron.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Numbers

What do the symbols in F = BQv mean, and what units do they take?

Numbers

When does F = BQv apply, and how is Fleming's left-hand rule used for a positive charge?

Numbers

Why does a charged particle follow a circular path in a uniform magnetic field?

Numbers

How is the radius of the circular path found, and what provides the centripetal force?

Numbers

What is cyclotron frequency, and why is it independent of the particle's speed?

Questions from this subtopic

Each one with the model answer underneath.

1
In the equation F = BQv for the force on a moving charge, what does B represent and what is its unit?
Model answer
B represents magnetic flux density, measured in tesla (T).
2
In the equation F = BQv, what does Q represent and what is its unit?
Model answer
Q represents the charge of the particle, measured in coulombs (C).
3
State the formula for the force on a charged particle moving in a magnetic field.
Model answer
F = BQv, where B is magnetic flux density, Q is charge, and v is velocity.
4
Calculate the magnetic force when magnetic flux density = 1.09 T, charge = 1.60 × 10⁻¹⁹ C, velocity = 1.12 × 10⁶ m s⁻¹.
Model answer
Magnetic force = 1.09 × 1.60 × 10⁻¹⁹ × 1.12 × 10⁶ = 1.95 × 10⁻¹³ N.
5
Under what condition regarding the angle between velocity and field does the formula F = BQv apply?
Model answer
The formula applies only when the magnetic field is perpendicular to the velocity of the charged particle.
6
When using Fleming's left-hand rule for a positive charge in a magnetic field, what does the thumb represent?
Model answer
The thumb represents the direction of the force on the charged particle.

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