Determination of specific charge of an electron - Thomsons method

Summary

In Thompson's experiment, a uniform magnetic field is applied perpendicular to an electric field, and Fleming's Left-Hand Rule is used to determine the direction of force on a beam of electrons. By adjusting the magnetic field, the effect of the electric field is canceled out, and the forces on the electrons from both fields are balanced. This allows the electron beam to be precisely controlled, demonstrating how the magnetic field impacts the motion of charged particles. The experiment showcases the interplay of electric and magnetic forces and the essential role of Fleming's Left-Hand Rule in understanding particle behavior.

Takeaways

• 😀 A uniform magnetic field is created using an electromagnet perpendicular to the electric field.
• 😀 The magnetic field flows from the North Pole to the South Pole of the electromagnet.
• 😀 Fleming's left hand rule helps to determine the direction of motion for charged particles.
• 😀 The index finger points to the direction of the magnetic field in Fleming's left hand rule.
• 😀 The middle finger points to the direction of the current, which is opposite to the direction of the electron flow.
• 😀 The thumb in Fleming's left hand rule indicates the direction of the electron's motion or thrust.
• 😀 Electrons, which are negatively charged, move opposite to the current flow.
• 😀 The electron beam moves upwards as the magnetic field causes a force on the electrons.
• 😀 The displacement of the electron beam is proportional to the magnitude of the magnetic field.
• 😀 Adjusting the magnetic field cancels out the effect of the electric field, keeping the beam at point P.
• 😀 The force on the electron due to the electric field equals the force on the electron due to the magnetic field.

Q & A

What is the role of the uniform magnetic field in Thompson's experiment?

The uniform magnetic field, created by an electromagnet, is perpendicular to the electric field applied by the metal plates. It influences the movement of the electron beam, causing it to experience a magnetic force.

How does Fleming's Left-Hand Rule apply in this experiment?

Fleming's Left-Hand Rule helps determine the direction of the force on a charged particle, like an electron, in the presence of both electric and magnetic fields. The index finger represents the magnetic field, the middle finger represents the electric current, and the thumb points in the direction of the motion of the electron beam.

Why is the direction of the current opposite to the direction of the electron flow?

The electron flow is in the opposite direction to the conventional current because electrons are negatively charged. Current is defined as the flow of positive charge, which is opposite to the actual movement of electrons.

What happens when the magnetic field is increased in this experiment?

When the magnetic field is increased, the displacement of the electron beam increases, causing the beam to move further upward. The magnetic field strength affects the amount of force exerted on the electrons.

How is the effect of the electric field canceled out in the experiment?

The effect of the electric field is canceled by adjusting the magnetic field so that the force from the magnetic field exactly balances the force from the electric field, resulting in no net force on the electron beam.

What does the term 'force on the electron' refer to in this experiment?

The 'force on the electron' refers to the interaction between the electric field and the magnetic field, which causes the electrons to move in a specific direction. The net force on the electron results from both fields acting on it.

How is the force on the electron due to the magnetic field different from the force due to the electric field?

The force due to the magnetic field depends on the velocity of the electrons and the strength of the magnetic field. The force due to the electric field depends on the charge of the electron and the strength of the electric field. The two forces act on the electron in different ways but can be balanced in this experiment.

What is the significance of the point P mentioned in the experiment?

Point P is the specific location where the electron beam is adjusted to reach when the magnetic field is applied. It represents the point at which the forces from the electric and magnetic fields balance out, causing the electron beam to stabilize.

Why does the electron beam move upwards in this setup?

The electron beam moves upward because the direction of the force from the magnetic field (as indicated by Fleming's Left-Hand Rule) is upward, and this motion compensates for the force from the electric field.

What does the term 'displacement proportional to the magnetic field' mean in this context?

This means that the vertical displacement of the electron beam increases as the magnetic field strength increases. The stronger the magnetic field, the further the beam moves upward, showing a direct proportional relationship between the magnetic field and displacement.