Physics: Discovery of Electron

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What device was used by William Crooks to study the conduction of electricity through gases?

Vacuum chamber

Conductivity cell

Incandescent bulb

Discharge tube (correct)

What behavior is exhibited by cathode rays when an electric field is applied?

They travel in a circular path.

They are absorbed by the anode.

They scatter in all directions.

They are deflected towards the positive plate. (correct)

Who first experimentally determined the charge/mass ratio of electrons?

Niels Bohr

Albert Einstein

J.J. Thomson (correct)

Ernest Rutherford

Which of the following is NOT a property of cathode rays?

They can pass through any material. Signup and view all the answers

What is the function of the electrodes in a discharge tube?

To conduct electricity Signup and view all the answers

What indicates the presence of negative charge in cathode rays?

Deflection towards the positive plate Signup and view all the answers

What happens to the current in the discharge tube at low pressures?

It can only flow at high voltages. Signup and view all the answers

What material can glow when hit by cathode rays?

Fluorescent materials Signup and view all the answers

What factor does NOT affect the deflection of particles in an electric or magnetic field?

Type of gas in the discharge tube Signup and view all the answers

What is the value of the charge to mass ratio of the electron as determined by Thomson?

$1.758820 x 10^{11} C/kg$ Signup and view all the answers

Which of the following statements about anode rays is true?

They carry a positive charge depending on the gas used. Signup and view all the answers

What particle is considered the smallest and lightest positive ion?

Proton Signup and view all the answers

What aspect of neutrons was discovered by Chadwick?

They are neutral particles formed from a- particles. Signup and view all the answers

In Thomson's model of the atom, where are the negatively charged electrons located?

Embedded within a positively charged sphere Signup and view all the answers

The properties of which type of rays are opposite to those of electrons?

Positive rays or anode rays Signup and view all the answers

Which of the following is NOT true regarding the charge to mass ratio of the particles in anode rays?

It is always equal to the charge of an electron. Signup and view all the answers

Study Notes

Discovery of Electron

In 1879, William Crooks conducted experiments on electricity conduction through low-pressure gases using a discharge tube.
The discharge tube is a 60 cm long cylindrical glass tube with two metal electrodes, sealed at both ends.
Electrical discharge is observable only at low pressures and high voltages, leading to the flow of particles known as cathode rays from the cathode to the anode.

Properties of Cathode Rays

Cathode rays travel in straight lines and originate from the cathode moving towards the anode.
They are invisible directly but can cause fluorescent materials to glow upon contact.
Cathode rays consist of negatively charged particles, demonstrated by their deflection towards a positive plate in an electric field.
Characteristics of cathode rays remain consistent regardless of the electrode material or gas type in the tube.

Discovery of Charge/Mass Ratio for Electrons

J.J. Thomson experimentally determined the charge/mass ratio (e/m) of electrons using electric and magnetic fields.
The degree of deflection of the particles depends on the charge magnitude, the particle's mass, and the strength of the electric/magnetic fields.
Thomson calculated the charge/mass ratio to be e/m = 1.758820 x 10^11 C kg^-1.

Charge on the Electron

R.A. Millikan's oil drop experiment was critical for determining the charge of an electron.

Discovery of Proton

In 1886, Goldstein modified the discharge tube with a perforated cathode, observing luminous rays called anode rays emerging through the perforations.
Anode rays move in the opposite direction to cathode rays and are generated between the anode and cathode.
The charge on particles in anode rays varies based on the gas used, and the charge/mass ratio also differs.

Properties of Anode Rays

Positive charge (e) of particles is gas-dependent, and some particles carry multiples of the fundamental electrical charge.
The behavior of anode rays in magnetic or electric fields is contrary to that of cathode rays.

Proton Characteristics

The smallest positive ion, the proton, originates from hydrogen.
The mass of a proton is 1.676 x 10^-27 kg, and its charge is +1.602 x 10^-19 C.

Discovery of Neutron

Neutrons, neutral particles, were discovered by Chadwick in 1932 through the bombarding of beryllium with alpha particles, resulting in highly penetrating neutral rays.

Thomson Model of Atom

J.J. Thomson proposed that an atom is a positively charged sphere, with embedded negatively charged electrons, suggesting a uniform distribution of charge.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Explore the groundbreaking experiments that led to the discovery of electrons, including the work of William Crooks and J.J. Thomson. This quiz covers the properties of cathode rays and their significance in understanding electrical conduction. Test your knowledge on the historical experiments that shaped modern physics.