What do the thumb, first finger and second finger represent in Fleming's left-hand rule?

Thumb = Force / motion ( F ) First finger = Field ( B ) Second finger = Current ( I )

In which direction does the current point in Fleming's left-hand rule (second finger)?

The direction of conventional current , from positive to negative .

True or False? Dots are used to represent a magnetic field directed into the page.

False. Dots represent a field directed out of the page; crosses represent a field directed into the page.

Fleming's left-hand rule is used to find the current, field and force for a current-carrying conductor, which are all .......... to each other.

Fleming's left-hand rule is used to find the current, field and force for a current-carrying conductor, which are all mutually perpendicular to each other.

True or False? A charged particle travelling parallel to a magnetic field experiences the maximum possible magnetic force.

False. It experiences no force when travelling parallel to the field; the maximum force occurs when it travels perpendicular to the field.

How does the direction of conventional current relate to the velocity of a moving charged particle, for positive and negative charges?

For a positive charge, the current points in the same direction as its velocity For a negative charge, the current points in the opposite direction to its velocity

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

The magnetic force is always perpendicular to the particle's velocity, continuously changing its direction of motion.

In the equation F = BQv sin θ, θ is the angle between the particle's .......... and the magnetic field.

In the equation F = BQv sin θ, θ is the angle between the particle's velocity and the magnetic field.

Define Hall voltage .

The Hall voltage is the potential difference produced across an electrical conductor when an external magnetic field is applied perpendicular to the current through the conductor.

Why does a potential difference build up across a current-carrying conductor placed in a perpendicular magnetic field?

The magnetic force deflects the moving charge carriers to one side of the conductor, making that side more charged than the other. This charge separation produces the Hall voltage .

True or False? If the charge carriers in a conductor were positive rather than negative, the Hall voltage would be in the same direction, provided the current is unchanged.

False. Positive charge carriers experience a magnetic force in the opposite direction to electrons for the same current, so the charge separation reverses and the Hall voltage direction reverses.

In a Hall probe, charge carriers experience a magnetic force perpendicular to their direction of .......... , causing them to accumulate on one side of the conductor.

In a Hall probe, charge carriers experience a magnetic force perpendicular to their direction of drift , causing them to accumulate on one side of the conductor.

A Hall probe is a device used to measure magnetic flux density, based on the Hall effect. It consists of a cylinder with a flat sensing surface at one end.

How must the flat surface of a Hall probe be oriented to obtain the maximum voltmeter reading?

Perpendicular to the magnetic field lines, so the field passes completely through the flat surface.

Why can the reading from a Hall probe be used to determine the magnetic flux density of a field?

The Hall voltage produced is directly proportional to the magnetic flux density , so the flux density can be found from the voltmeter reading.

If a Hall probe is not held perpendicular to the field lines, the voltmeter reading will be .......... .

If a Hall probe is not held perpendicular to the field lines, the voltmeter reading will be reduced .

True or False? A Hall probe is too insensitive to detect the Earth's magnetic flux density.

False. A Hall probe is sensitive enough to measure even the Earth's magnetic flux density.

Why does a charged particle travel in a circular path when it enters a uniform magnetic field?

The magnetic force on the particle is always perpendicular to its velocity and directed towards the centre of the path, so it acts as a centripetal force , producing circular motion.

The centripetal acceleration of a charged particle moving in a magnetic field acts in the same direction as the .......... force.

The centripetal acceleration of a charged particle moving in a magnetic field acts in the same direction as the centripetal (magnetic) force.

Define velocity selector .

A velocity selector is a device consisting of perpendicular electric and magnetic fields where charged particles with a specific velocity can be filtered.

What happens to particles in the beam whose speed is not equal to the selected velocity v ?

The electric and magnetic forces on them are unequal, so they are deflected and collide with one of the charged plates, removing them from the beam.

True or False? The gravitational force on the charged particles must be included when calculating the selected velocity in a velocity selector.

False. The gravitational force is negligible compared to the electric and magnetic forces, so it can be ignored.

For a charged particle to pass through a velocity selector undeflected, the electric force must be equal and opposite to the .......... force.

For a charged particle to pass through a velocity selector undeflected, the electric force must be equal and opposite to the magnetic force.

A LevelPhysicsCambridge (CIE)Flashcards20. Magnetic FieldsForce on a Moving Charge

Force on a Moving Charge (Cambridge (CIE) A Level Physics): Flashcards

Exam code: 9702

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FrontFleming's Left-Hand Rule
What do the thumb, first finger and second finger represent in Fleming's left-hand rule?
BackFleming's Left-Hand Rule
Thumb = Force / motion (F)
First finger = Field (B)
Second finger = Current (I)
BackFleming's Left-Hand Rule
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Cards in this collection (34)

What do the thumb, first finger and second finger represent in Fleming's left-hand rule?
- Thumb = Force / motion (F)
- First finger = Field (B)
- Second finger = Current (I)
In which direction does the current point in Fleming's left-hand rule (second finger)?
The direction of conventional current, from positive to negative.
True or False?
Dots are used to represent a magnetic field directed into the page.
False.
Dots represent a field directed out of the page; crosses represent a field directed into the page.
Fleming's left-hand rule is used to find the current, field and force for a current-carrying conductor, which are all .......... to each other.
Fleming's left-hand rule is used to find the current, field and force for a current-carrying conductor, which are all mutually perpendicular to each other.
State the equation for the magnetic force F on an isolated charged particle moving at speed v at angle θ to a magnetic field of flux density B.
$F = B Q v s i n θ$
What is the equation for the magnetic force on a charged particle when it travels perpendicular to the field?
$F = B Q v$ since sin θ = 1 when θ = 90°.
True or False?
A charged particle travelling parallel to a magnetic field experiences the maximum possible magnetic force.
False.
It experiences no force when travelling parallel to the field; the maximum force occurs when it travels perpendicular to the field.
How does the direction of conventional current relate to the velocity of a moving charged particle, for positive and negative charges?
- For a positive charge, the current points in the same direction as its velocity
- For a negative charge, the current points in the opposite direction to its velocity
Why does a charged particle moving in a uniform magnetic field follow a circular path?
The magnetic force is always perpendicular to the particle's velocity, continuously changing its direction of motion.
In the equation F = BQv sin θ, θ is the angle between the particle's .......... and the magnetic field.
In the equation F = BQv sin θ, θ is the angle between the particle's velocity and the magnetic field.
Define Hall voltage.
The Hall voltage is the potential difference produced across an electrical conductor when an external magnetic field is applied perpendicular to the current through the conductor.
Why does a potential difference build up across a current-carrying conductor placed in a perpendicular magnetic field?
The magnetic force deflects the moving charge carriers to one side of the conductor, making that side more charged than the other. This charge separation produces the Hall voltage.
State the equation for the Hall voltage $V_{H}$ in terms of magnetic flux density B, current I, number density n, thickness t and charge q.
$V_{H} = \frac{B I}{n t q}$
Why is a semiconductor used as the sensing element of a Hall probe, rather than a metal?
Semiconductors have a much smaller number density of charge carriers n than metals. Since $V_{H} \propto \frac{1}{n}$ , this produces a larger, more measurable Hall voltage.
True or False?
If the charge carriers in a conductor were positive rather than negative, the Hall voltage would be in the same direction, provided the current is unchanged.
False.
Positive charge carriers experience a magnetic force in the opposite direction to electrons for the same current, so the charge separation reverses and the Hall voltage direction reverses.
In a Hall probe, charge carriers experience a magnetic force perpendicular to their direction of .........., causing them to accumulate on one side of the conductor.
In a Hall probe, charge carriers experience a magnetic force perpendicular to their direction of drift, causing them to accumulate on one side of the conductor.
Define Hall probe.
A Hall probe is a device used to measure magnetic flux density, based on the Hall effect. It consists of a cylinder with a flat sensing surface at one end.
What is a Hall probe connected to, in order to measure the Hall voltage it produces?
A voltmeter.
How must the flat surface of a Hall probe be oriented to obtain the maximum voltmeter reading?
Perpendicular to the magnetic field lines, so the field passes completely through the flat surface.
Why can the reading from a Hall probe be used to determine the magnetic flux density of a field?
The Hall voltage produced is directly proportional to the magnetic flux density, so the flux density can be found from the voltmeter reading.
If a Hall probe is not held perpendicular to the field lines, the voltmeter reading will be ...........
If a Hall probe is not held perpendicular to the field lines, the voltmeter reading will be reduced.
True or False?
A Hall probe is too insensitive to detect the Earth's magnetic flux density.
False.
A Hall probe is sensitive enough to measure even the Earth's magnetic flux density.
Why does a charged particle travel in a circular path when it enters a uniform magnetic field?
The magnetic force on the particle is always perpendicular to its velocity and directed towards the centre of the path, so it acts as a centripetal force, producing circular motion.
State the equation for the radius r of the circular path of a charged particle in a perpendicular magnetic field.
$r = \frac{m v}{B Q}$
where m = mass, v = speed, B = magnetic flux density, Q = charge.
How does the radius of the circular path depend on the speed and mass of the charged particle?
The radius is directly proportional to both:
- speed, $r \propto v$
- mass, $r \propto m$
How does the radius of the circular path depend on the charge of the particle and the magnetic flux density?
The radius is inversely proportional to both:
- charge, $r \propto \frac{1}{Q}$
- magnetic flux density, $r \propto \frac{1}{B}$
True or False?
A particle with a greater charge moves in a larger radius circular path.
False.
The radius is inversely proportional to the charge, $r \propto \frac{1}{Q}$ , so a greater charge produces a smaller radius.
The centripetal acceleration of a charged particle moving in a magnetic field acts in the same direction as the .......... force.
The centripetal acceleration of a charged particle moving in a magnetic field acts in the same direction as the centripetal (magnetic) force.
Define velocity selector.
A velocity selector is a device consisting of perpendicular electric and magnetic fields where charged particles with a specific velocity can be filtered.
Why does the electric force on a charged particle in a velocity selector not depend on its speed, while the magnetic force does?
The electric force is $F_{E} = E Q$ (no velocity term), but the magnetic force is $F_{B} = B Q v$ , which increases with speed v.
Derive the equation for the selected velocity v of a velocity selector, in terms of electric field strength E and magnetic flux density B.
For undeflected particles, $F_{E} = F_{B}$ , so $E Q = B Q v$ . The charge Q cancels, giving:
$v = \frac{E}{B}$
What happens to particles in the beam whose speed is not equal to the selected velocity v?
The electric and magnetic forces on them are unequal, so they are deflected and collide with one of the charged plates, removing them from the beam.
True or False?
The gravitational force on the charged particles must be included when calculating the selected velocity in a velocity selector.
False.
The gravitational force is negligible compared to the electric and magnetic forces, so it can be ignored.
For a charged particle to pass through a velocity selector undeflected, the electric force must be equal and opposite to the .......... force.
For a charged particle to pass through a velocity selector undeflected, the electric force must be equal and opposite to the magnetic force.

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