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Modern Physics

Description: The test will revise the learnt concept.
Number of Questions: 15
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Tags: Thermionic emission Cathode ray tube Atomic structure Radioactivity radioactive radiation etc. Thermoinic Emission Modern Physics Nuclear Radiations Precautions
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Which of the following statements are incorrect for a nucleus of an atom? (a) The size of nucleus is of the order of 10-5 m. (b) It contains nucleons naming proton and neutron. (c) The total number of nucleons determines its atomic number. (d) The mass of nucleus of an atom is approximately equal to the product of its mass number and the number of proton.

  1. Both (a) and (b)

  2. Both (b) and (c)

  3. Both (c) and (d)

  4. Both (a) and (c)

  5. Both (b) and (d)

Show answer
Correct Option: D
Explanation:

The size of a nucleus is of the order 10-14 m. The total number of nucleons determines the atomic mass of an atom. Here, both the statements are incorrect.

Which of the following statements are correct for work function? (a) It is defined as the energy required for emitting electrons from metallic surface. (b) Its value is generally expressed in joule. (c) It is a characteristic of a metal. (d) The work function for alkali metals is very high.

  1. Both (a) and (b)

  2. Both (a) and (c)

  3. Both (b) and (c)

  4. Both (b) and (d)

  5. Both (a) and (d)

Show answer
Correct Option: B
Explanation:

Work function is defined as the energy required for emitting electrons from metallic surface. It is a characteristic of a metal. Both the statements are correct.

Which of the following is a condition for existence of a radioactive element?

  1. The number of protons and neutrons are nearly equal.

  2. The number of protons exceeds much more than that of the neutrons.

  3. The number of neutrons exceeds much more than that of the protons.

  4. The number of protons exceeds much more than that of the electrons.

  5. The number of electrons exceeds much more than that of the neutrons.

Show answer
Correct Option: C
Explanation:

When the number of neutrons exceeds much than that of the protons in a nucleus, it becomes unstable or radioactive.

Which of the following does not affect the rate of thermionic emission?

  1. Nature of the metal

  2. Temperature of surface of the metal

  3. Shape of the metal

  4. Both temperature and shape of the metal

  5. Both temperature and surface area of the metal

Show answer
Correct Option: C
Explanation:

Thermionic emission does not depend on the shape of the metal.

The atomic and mass number of an atom of an element are 27 and 60 respectively. Which of the following statements are incorrect conclusions for the given data? (a) The name of the element is potassium. (b) It is a radioactive element. (c) The atom contains 33 neutrons in its nucleus. (d) It is a radioisotope of cobalt. (e) The ratio of neutron to the proton is less than 1.

  1. Both (a) and (b)

  2. Both (a) and (c)

  3. Only (a) and (e)

  4. Both (a) and (d)

  5. Both (b) and (c)

Show answer
Correct Option: C
Explanation:

Here, the ratio of number of neutrons to that of protons is greater than 1, which means that it is an unstable element. Hence, it is a radioisotope of cobalt.

A student of class 10 of ICSE board gives the clues in the form of reasons for the emission of beta particle to one of his classmates who recently studied the chapter of modern physics. Which of the following clues should he choose to reach the correct reason for this?

  1. An electron of outer orbit comes out of an atom after being exited.

  2. A proton disintegrates into neutron and electron, and this electron comes out of an atom.

  3. A neutron disintegrates into proton and electron, and this electron comes out of an atom.

  4. An electron of inner orbit falls into the nucleus, and finally comes out of an atom.

  5. A neutron strikes the electron of inner orbit and expels it out as a beta particle.

Show answer
Correct Option: C
Explanation:

An atom in which the ratio of neutrons and protons exceeds unity is unstable. A neutron disintegrates into proton and electron and this electron comes out of an atom.

Which of the following is a result of an alpha emission from a radioactive element?

  1. The atomic number of the daughter element is increaseed by 2.

  2. The atomic number of the daughter element is decreased by 2.

  3. The mass number of the daughter element is increased by 4.

  4. Atomic number of daughter element is increased by 2, and mass number is increased by 4.

  5. Atomic number of daughter element is decreased by 2, and mass number is decreased by 4.

Show answer
Correct Option: E
Explanation:

When an alpha particle comes out of the nucleus of a radioactive element, the atomic number and the mass number decrease by 2 and 4 respectively.

Which of the following helps in explaining the phenomenon of radioactivity?

  1. Law of conservation of mass

  2. Law of conservation of charge

  3. Law of conservation of mass and charge

  4. Law of constant and multiple proportion

  5. Law of conservation of charge and constant proportion

Show answer
Correct Option: C
Explanation:

Both the mass and charge remain conserved during disintegration of a radioactive element.

Which of the following elements is not correctly matched with its work function?

  1. Platinum: 6.2 eV

  2. Chromium: 4.52 eV

  3. Zinc: 2.3 eV

  4. Potassium: 2.26 eV

  5. Tungsten: 4.52 eV

Show answer
Correct Option: C
Explanation:

The work function of zinc is 4.24 eV.

Which of the following are known as tracers in the field of medical science? (a) Cobalt-60 (b) Radio-sodium chloride (c) Radio-iodine (d) Gamma rays

  1. Both (a) and (b)

  2. Both (b) and (c)

  3. Both (a) and (c)

  4. Both (a) and (d)

  5. Both (b) and (d)

Show answer
Correct Option: B
Explanation:

Both radio-sodium chloride and radio-iodine are used in the field of medical science as tracers to detect brain tumor and blood clotting in the body.

Which of the following information about an alpha particle is not correct?

  1. The mass of an alpha particle is 6.68 x 10-27 kg.

  2. Its charge is + 3.2 x 10-19 coulomb.

  3. Its specific charge is 1.76 x 1011coulomb per kilogram.

  4. It is deflected in both electric and magnetic field.

  5. It is used for transmutation.

Show answer
Correct Option: C
Explanation:

The specific charge of an alpha particle is 4.79 x 107 coulombs per kilogram.

What of the following is not correct about background radiation?

  1. They are radiations to which we all are exposed even in the absence of visible radioactive sources.

  2. Radium, K-40 and C-14 are some of the sources of these radiations.

  3. They cause serious biological damage to us.

  4. Gamma radiations come from the radioactive rocks in the earth's crust.

  5. They do not exceed the maximum permissible level for human safety.

Show answer
Correct Option: C
Explanation:

The background radiations do not cause serious biological damage to us because they do not exceed the maximum permissible level for human safety.

Which of the following is not correct for gamma radiations? (a) Gamma radiations occur when the parent nucleus is in a state of excitation. (b) They are the electromagnetic waves. (c) Their ionising power is very high. (d) They affect a photographic plate. (e) They do not cause fluorescence.

  1. Only (a)

  2. Only (b)

  3. Both (a) and (c)

  4. Both (b) and (d)

  5. Both (c) and (e)

Show answer
Correct Option: D
Explanation:

The ionising power of gamma radiations is very low as they are not composed of charged particles like alpha and beta particles. They cause fluorescence when they are incident on a fluorescent material.

Which of the following radio isotopes are largely found in the bones, and affect only the bones and reproductive organs of humans?

  1. Radium

  2. Potassium-40

  3. Carbon -14

  4. Carbon -12

  5. Radio-iodine

Show answer
Correct Option: A
Explanation:

Radium is largely found in the bones, and affect only the bones and reproductive organs of humans.

Which of the following is considered as a helping hand in the manufacture of paper, plastic and metallic sheets?

  1. Alpha rays

  2. UV rays

  3. Gamma rays

  4. Cosmic rays

  5. X-rays

Show answer
Correct Option: C
Explanation:

Gamma rays have the maximum penetrating power and therefore, they are used to control the thickness of paper, plastic and metallic sheets during their manufacture.

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