Atomic Structure and Cathode Rays

Test your knowledge on the fundamental particles of an atom, early atomic models, and the discovery of the electron through cathode ray experiments.

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1. According to the text, who is credited with coining the term 'atom'?

J.J. Thomson Rutherford John Dalton A.O. Rajee

Explanation: The text explicitly states, 'John Dalton coined the term atom.'

2. What conditions are necessary for the production of cathode rays in a discharge tube as described in the document?

High voltage and high pressure Low voltage and very low pressure High voltage and very low pressure Low voltage and high pressure

Explanation: The section 'Discovery of electron - study of Cathode rays' mentions that J.J. Thomson observed the effect 'when a high voltage is applied between the electrodes fitted in discharge tube, at a very low pressure'.

3. Why is an atom considered electrically neutral as a whole?

It contains only neutrons. The number of protons equals the number of electrons. The number of protons equals the number of neutrons. It lacks any charged particles.

Explanation: The text states: 'In fact, the atom as the whole is electrically neutral as number of protons in it is equal to number of electrons.'

4. Based on the diagram and text, from which electrode do the cathode rays originate?

The anode (positive electrode) The cathode (negative electrode) The vacuum pump inlet The glass wall of the tube

Explanation: The diagram labels the negative electrode as the 'Cathode' and shows 'Cathode rays' emerging from it. The text also mentions that radiations are 'emitted from the cathode'.

5. Under what condition will no electric current flow through the discharge tube?

When the gas pressure is very low When the voltage is very high When the gas pressure is 1 atm When a vacuum pump is attached

Explanation: The text notes that 'when the gas pressure in the tube is 1 atm, no electric current flows through the tube. This is because the gases are poor conductor of electricity.'

6. What is the described origin of cathode rays?

Spontaneous emission from the gas molecules. A chemical reaction with the glass tube. High-speed electrons emitted first from the anode. Bombardment of gas molecules by high-speed electrons emitted from the cathode.

Explanation: Under 'Origin of Cathode rays', the text explains they are 'produced in cathode due to bombardment of the gas molecules by the high-speed electrons emitted first from the cathode.'

7. What visible effect do the cathode rays produce in the experiment?

A bright white flash A faint green glow on the tube wall A purple light filling the tube Sparks between the electrodes

Explanation: The text says the 'wall of the discharge tube near cathode starts glowing,' and the diagram specifically labels this phenomenon as a 'Faint green glow'.

8. According to the introductory paragraph, what does modern physics suggest about the 'solar system' model of the atom?

It is a completely accurate representation. It may be useful in some circumstances but is ultimately incorrect. It is too complex for nonscientists to understand. It was proposed by J.J. Thomson.

Explanation: The introduction states, 'In some circumstances, this "solar system" model of the atom may be useful, but you should know that the electron is much more unusual than that model suggests.'

9. Which of the following is NOT listed as an 'AIM' of the lesson?

To introduce Fundamental particles To introduce Thomson's and Rutherford Atomic model To explain the principles of quantum mechanics To introduce terms like atomic number, mass number and isotopes

Explanation: The 'AIM' section lists introducing fundamental particles, atomic models, and terms like atomic number. It does not mention explaining quantum mechanics.

10. What did John Dalton consider the atom to be?

Composed of protons, neutrons, and electrons Easily divisible and destructible The fundamental particle of matter, indivisible and indestructible Electrically charged

Explanation: The text states, 'The atom is the fundamental particle of matter and considered to be indivisible and indestructible.'

11. According to the text, what are the negatively charged material particles that constitute cathode rays called?

Protons Anode rays Electrons Neutrons

Explanation: Point (iii) under 'Properties of Cathode rays' explicitly states, '...the negatively charged material particles constituting the cathode rays are called electrons.'

12. Who is credited with discovering the presence of positive rays (anode rays)?

Ernest Rutherford Goldstein J.J. Thomson Dr. A.O. Rajee

Explanation: The section 'Discovery of proton - study of Anode rays' begins with the sentence: 'Goldstein discovered the presence of positive rays.'

13. Which of the following is NOT a property of cathode rays mentioned in the text?

They produce X-rays when striking hard metals. They travel in straight lines with high speed. Their nature depends on the gas inside the discharge tube. They cause ionization of the gas through which they pass.

Explanation: Point (x) under 'Properties of Cathode rays' states that 'The nature of the cathode rays does not depend upon the nature of the gas, taken in the discharge tube...'

14. What modification to the standard discharge tube was essential for the discovery of anode rays?

Using a heated anode Using a perforated cathode Coating the anode with zinc sulphide Increasing the gas pressure

Explanation: The text explains that Goldstein's experiment 'took perforated cathode and a gas at low pressure'. This allowed the positive rays to pass through the cathode and be observed.

15. How are anode rays (positive rays) formed in the discharge tube?

The anode emits positive particles. The cathode breaks down into positive fragments. Gas atoms in the tube lose electrons and become positively charged. Electrons combine to form positive particles.

Explanation: Under 'Origin of anode or positive rays,' the text states: 'In the discharge tube the atoms of gas lose negatively charged electrons. These atoms, thus, acquire a positive charge.'

16. How does the speed of anode rays compare to the speed of cathode rays, according to the text?

Anode rays are much faster. Their speeds are identical. Anode rays are much slower. Their speeds are dependent on the gas used.

Explanation: The first point under 'Properties of Anode rays' notes, 'They travel in straight lines. However, their speed is much less than that of the cathode rays.'

17. Who is credited with proving that the proton is a fundamental component of the nuclei of all atoms?

Goldstein J.J. Thomson Niels Bohr Ernest Rutherford

Explanation: The text states, 'The discovery of the proton is credited to Ernest Rutherford, who proved that the nucleus of the hydrogen atom (i.e. a proton) is present in the nuclei of all other atoms...'

18. What is the charge-to-mass (e/m) ratio for cathode rays described as?

Constant Variable Dependent on the anode material Dependent on the gas pressure

Explanation: Point (xi) under 'Properties of Cathode rays' states: 'For each cathode rays, the ratio of charge (e) to mass (m) is constant.'

19. What phenomenon occurs when cathode rays strike the glass walls of the discharge tube coated with zinc sulphide?

The glass melts. A loud sound is produced. Green fluorescence is produced. The tube becomes magnetic.

Explanation: Point (vii) under 'Properties of Cathode rays' mentions: 'They produce green fluorescence on the glass walls of the discharge tube exp : zinc sulphide.'

20. Based on the diagram and text, what is the purpose of the ZnS coating in the experiment for producing anode rays?

To act as the positive electrode. To absorb excess electrons. To make the invisible anode rays visible through fluorescence. To keep the tube at a low temperature.

Explanation: The text explains that the new rays coming through the cathode 'gives fluorescence on the opposite glass wall coated with zinc sulphide.' This indicates the ZnS coating serves as a detector.

21. According to the document, who discovered the neutron?

J.J. Thomson Ernest Rutherford Chadwick Millikan

Explanation: The text under the 'Neutron' section explicitly states, 'It was discovered by Chadwick by bombarding Be atom with high speed α-particles.'

22. What is the charge of an electron as determined by Millikan's oil drop experiment?

+1.602 x 10⁻¹⁹ coulombs -1.602 x 10⁻¹⁹ coulombs 9.11 x 10⁻²⁸ coulombs Zero

Explanation: Under the 'Electron' section, the text states the charge was determined by Millikan's oil drop experiment as -1.602x10⁻¹⁹ coulombs.

23. Based on the text, which fundamental particle is described as the heaviest and least stable?

Electron Proton Neutron Alpha Particle

Explanation: In the 'Neutron' section, the last point states: 'Among all the elementary particles neutron is the heaviest and least stable.'

24. The nature and charge-to-mass ratio of anode rays depend on what factor?

The material of the cathode The voltage applied across the tube The gas taken in the discharge tube The material of the anode

Explanation: Points (iv) and (v) at the beginning of the text state that the nature of anode rays and their charge-to-mass ratio depend on the gas used in the discharge tube.

25. According to the table, where are neutrons located within an atom?

Outside the nucleus In the nucleus Orbiting the nucleus In the electron shells

Explanation: The summary table at the bottom of the page lists the location for both the Proton and Neutron as 'In the nucleus'.

26. How many times heavier is a proton compared to an electron, as mentioned in the notes?

1837 times 1/1837th 0.18% They have the same mass

Explanation: Under the 'Proton' section, the text says about its mass: 'It is 1837 times heavier than an electron.'

27. What is the value of the charge on one mole of electrons?

0.55 mg 1.76x10⁸ coulombs 96500 coulombs 1.602x10⁻¹⁹ coulombs

Explanation: The 'Electron' section states: 'Charge on one mole of electron is 96500 coulombs or 1 faraday.'

28. Which of these particles has a specific charge (e/m ratio) of zero?

Electron Proton Neutron Anode ray particle

Explanation: The notes for the 'Neutron' state, 'Specific charge: It is zero.' This is because its electrical charge (e) is zero.

29. According to the summary table, what is the mass of a proton in kilograms?

9.109x10⁻³¹ kg 1.672x10⁻²⁷ kg 1.675x10⁻²⁷ kg 1.6022x10⁻¹⁹ kg

Explanation: The table under the 'Proton' column and 'Mass' row lists the value as 1.672x10⁻²⁷ kg.

30. The discovery of the proton is credited to which scientist?

J.J. Thomson Chadwick Millikan Ernest Rutherford

Explanation: The text under section '2. Proton' starts with 'The discovery of the proton is credited to Ernest Rutherford'.

31. According to Thomson's Atomic Model, what is the structure of an atom?

A central positive nucleus with electrons orbiting it. A sphere of positive charge with electrons embedded in it. A solid, indivisible particle with no internal structure. A cloud of electrons surrounding a small, dense nucleus.

Explanation: The text states that in Thomson's model, 'an atom is a sphere of positive charge having a number of embedded electrons in it and sufficient enough to neutralize the positive charge.'

32. Thomson's model is also known by what other names mentioned in the text?

Planetary model or nuclear model Billiard ball model or solid sphere model Watermelon model or plum pudding model Quantum mechanical model or cloud model

Explanation: The text explicitly says, 'This model, sometime called watermelon model or raisin or plum pudding model.'

33. What was a major limitation of Thomson's Atomic Model as stated in the document?

It couldn't explain the existence of isotopes. It did not account for the atom's neutral charge. It failed to explain the results of Rutherford's scattering experiment. It contradicted the law of conservation of mass.

Explanation: Under the 'Limitation' section, the text notes, 'This model failed [to] explain the results of scattering experiment of Rutherford and the stability of atom.'

34. In Rutherford's alpha-ray scattering experiment, what was the purpose of the zinc sulphide screen?

To generate the alpha particles. To act as the target for the alpha particles. To focus the beam of alpha particles. To detect the alpha particles after they struck the foil.

Explanation: The text mentions that the presence of alpha particles 'was detected with the help of a circular zinc sulphide screen' which would produce 'a flash of light' upon being struck.

35. What type of particles were used to bombard the thin metal foil in Rutherford's experiment?

Electrons Beta particles Alpha particles Neutrons

Explanation: The section is titled 'Rutherford's Atomic Model' and details his 'α-ray scattering experiment' using a 'beam of fast moving radioactive particles' (alpha particles).

36. What was the most common observation in Rutherford's gold foil experiment, according to the text?

Most of the α-particles were deflected at large angles. All of the α-particles were absorbed by the foil. A small fraction of α-particles bounced straight back. Most of the α-particles passed through the foil without any deflection.

Explanation: The first point under 'Observations and Conclusions' states, 'Most of the α-particles passed through the gold foil without any deflection from their original path.'

37. What primary conclusion was drawn from the observation that most alpha particles passed straight through the gold foil?

The atom is a solid sphere of positive charge. The atom is largely empty space. Electrons are located in the nucleus. The gold foil was too thin to affect the particles.

Explanation: The text explains this observation by stating, 'Bcz [because] atom has largely empty space as most of the α-particles passed through the foil undeflected.'

38. What material was used for the thin foil in the diagram of Rutherford's experiment?

Silver Platinum Copper Gold

Explanation: While the text mentions other metals, the main diagram specifically labels the target as 'Gold foil (100 nm thickness)'.

39. According to the diagram of Rutherford's experimental setup, where did the beam of alpha particles originate?

From the zinc sulphide screen From the gold foil itself From a lead block containing a radioactive source From a particle accelerator

Explanation: The text says the particles 'originated from a lead block,' and the diagram shows a 'Radioactive source' housed in a block which produces the 'beam of alpha particles'.

40. How did Rutherford's findings challenge Thomson's model?

By proving atoms are divisible. By suggesting the atom's positive charge and mass are concentrated in a small nucleus, not spread out. By discovering the existence of the neutron. By showing that electrons have a negative charge.

Explanation: The observation that most alpha particles passed through undeflected, while a few were strongly deflected, contradicted Thomson's 'plum pudding' model of a diffuse positive charge. It led to the conclusion of a small, dense, positively charged nucleus in a mostly empty atom.

41. According to Rutherford's model as described in the text, what is primarily responsible for the mass of the atom?

The electrons orbiting the nucleus The extra nuclear part The nucleus The empty space within the atom

Explanation: Point 6 under 'According to Rutherford' states, 'As the nucleus of the atom is responsible for the mass of the atom...'

42. Why is Rutherford's model also referred to as the 'planetary model'?

Because it was discovered by an astronomer Because it has resemblances with the solar system Because atoms are spherical like planets Because electrons travel at the speed of light

Explanation: The text explicitly states in point 5, 'Rutherford's model has resemblances with solar system. Hence it's also known as planetary model of the atom.'

43. What was the main reason given for the deflection of a few alpha particles at large angles in Rutherford's experiment?

Collision with electrons Repulsion from a heavy positive charge at the atom's center The magnetic field of the atom The random motion of atoms in the foil

Explanation: The text explains this in point ii: '...there is heavy positive charge at the center of the atom which causes repulsions.'

44. Based on the drawbacks mentioned, what would happen to an electron according to Maxwell's electromagnetic theory?

It would gain energy and move to a higher orbit. It would maintain a stable orbit indefinitely. It would continuously lose energy and spiral into the nucleus. It would be ejected from the atom.

Explanation: Drawback 1 states that according to Maxwell's theory, a charged particle like an electron would lose energy continuously, 'move closer and closer to the nucleus following a spiral path', and ultimately 'fall into the nucleus'.

45. According to the text, why is an atom considered electrically neutral in Rutherford's model?

The nucleus contains an equal number of protons and neutrons. The number of extra nuclear electrons equals the number of positive charges in the nucleus. Atoms do not contain any charged particles. The positive charge is spread evenly throughout the atom.

Explanation: Point 4 explains, 'The number of extra nuclear electrons is equal to the number of units of positive charge in the nucleus. Therefore the atom is electrically neutral.'

46. What is the 'extra nuclear part' of the atom responsible for, as stated in the notes?

The atom's mass The atom's stability The atom's positive charge The atom's volume

Explanation: Point 6 clearly states, '...the extra nuclear part is responsible for its volume.'

47. What was the predicted atomic spectrum based on Rutherford's model, and how did it differ from the observed spectrum?

Predicted: Line spectrum; Observed: Continuous spectrum Predicted: Continuous spectrum; Observed: Line spectrum of well-defined frequencies Predicted: No spectrum; Observed: A single line spectrum Predicted: A spectrum in the UV range; Observed: A spectrum in the visible range

Explanation: Drawback 2 notes that if electrons lose energy continuously, 'the spectrum is expected to be continuous but the actual observed spectrum consists of well-defined lines of definite frequencies.'

48. Which of these statements is a central conclusion of Rutherford's model described in the text?

The atom is a solid, indivisible sphere. Electrons are embedded within a positively charged medium. The atom is mostly hollow with a small, positively charged nucleus. The nucleus is negatively charged.

Explanation: Points 1 and 2 under 'According to Rutherford' summarize this: 'Atom is spherical and mostly hollow with a lot of empty space...' and 'It has a small positively charged part at its center known as nucleus.'

49. The inability of Rutherford's model to explain which of the following is listed as a major drawback?

The existence of isotopes The electrical neutrality of the atom The stability of the atom The spherical shape of the atom

Explanation: The first drawback concludes that an electron spiraling into the nucleus would be 'making the atom unstable', and a later sentence says, 'Rutherford's model cannot explain the stability of the atom.'