What is the specific charge of the electron?

The ratio of the electron's charge to its mass, expressed as e/mₑ.

State the accepted value of the specific charge of the electron.

Approximately 1.76 × 10¹¹ C kg⁻¹.

In Thomson's experiment, how were cathode rays produced?

Cathode rays were produced in an evacuated tube.

How did Thomson apply an electric field to deflect the cathode ray beam?

An electric field was applied between parallel plates, which deflected the beam.

In what orientation was the magnetic field applied relative to the beam and electric field in Thomson's apparatus?

The magnetic field was applied perpendicular to both the beam and the electric field.

How did Thomson determine the velocity of the electrons when the beam was undeflected?

The electric and magnetic fields were adjusted until the beam was undeflected, giving v = E/B.

AQA A-Level Physics 7408

Measurements and Their Errors

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Particles and Radiation

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Turning Points in PhysicsOptional topic

Topic overview Cathode rays Thermionic emission of electrons Specific charge of the electron Principle of Millikan's determination of the electronic charge, e Newton's corpuscular theory of light Significance of Young's double slits experiment Electromagnetic waves The discovery of photoelectricity Wave–particle duality Electron microscopes The Michelson-Morley experiment Einstein's theory of special relativity Time dilation Length contraction Relativistic mass and energy

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Turning Points in Physics

Specific charge of the electron

4 things to know
Paper 3, section B

Overview

Thomson's experiment, balancing the electric and magnetic fields, and what the result implied.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Numbers

How was Thomson's magnetic field oriented, how did balancing the fields give the electron velocity, and what is v for E = 33500 V m⁻¹ and B = 0.0053 T?

Numbers

How is specific charge found from a circular path, and what does r represent?

Numbers

What did Thomson conclude about atomic structure, and why does high specific charge mean small mass?

Numbers

State the approximate value of the specific charge of the hydrogen ion

Questions from this subtopic

Each one with the model answer underneath.

1
What is the specific charge of the electron?
Model answer
The ratio of the electron's charge to its mass, expressed as e/mₑ.
2
State the accepted value of the specific charge of the electron.
Model answer
Approximately 1.76 × 10¹¹ C kg⁻¹.
3
In Thomson's experiment, how were cathode rays produced?
Model answer
Cathode rays were produced in an evacuated tube.
4
How did Thomson apply an electric field to deflect the cathode ray beam?
Model answer
An electric field was applied between parallel plates, which deflected the beam.
5
In what orientation was the magnetic field applied relative to the beam and electric field in Thomson's apparatus?
Model answer
The magnetic field was applied perpendicular to both the beam and the electric field.
6
How did Thomson determine the velocity of the electrons when the beam was undeflected?
Model answer
The electric and magnetic fields were adjusted until the beam was undeflected, giving v = E/B.

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