• Modern Physics - 1 (Class X)
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Modern Physics - 1 (Class X)

Description: Modern Physics - 1
Number of Questions: 15
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Tags: Modern Physics - 1 Thermionic Emission Hot Cathode Ray Tube and Diode Valve Production of X-rays and Its Uses Characteristics of α, β and γ Rays Nuclear Energy
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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.

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.

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 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.

Which of the following alternative energy sources pollute(s) the environment?

  1. Geothermal power plant

  2. Nuclear power plant

  3. Solar cells

  4. Both (1) and (3)

Show answer
Correct Option: B
Explanation:

During the process or reaction, a nuclear power plant gives the substance which pollutes the environment. Hence, option (2) is correct.

In which of the following electronic devices is the phenomenon of thermionic emission used?

(1) Diode valve (2) Radio (3) Stopwatch

  1. Only (3)

  2. Both (2) and (3)

  3. Only (1)

  4. Both (1) and (2)

Show answer
Correct Option: D
Explanation:

In diode valve and radio, the phenomenon of thermionic emission is used.

On which of the following factors does the rate of emission of electrons depend?

  1. Surface area of filament

  2. Temperature of filament

  3. Material used for filament

  4. Surface area and temperature of filament, and the material used for filament

Show answer
Correct Option: D
Explanation:

Thermionic emission is the emission of electrons from a heated filament or substance. When a filament like tungsten is heated to a high temperature, some electrons acquire sufficient energy and are able to break away from the surface of material and go into space. So, rate of emission of electrons depends upon surface area and temperature of filament and also on the material used for filament.

Which of the following is not correct regarding cathode ray tube?

  1. It is also called as Braun’s tube.

  2. Wehnelt cylinder is not used in cathode ray tube.

  3. It was invented by Karl Ferdinand Braun.

  4. It was invented in 1897.

Show answer
Correct Option: B
Explanation:

(1) The cathode ray tube was invented by the German Physicist Karl Ferdinand Braun in 1897 and is today used in computer monitors, TV sets etc. (2) The source of the electron beam is the electron gun which produces a stream of electrons through thermionic emission at heated cathode and focuses it into a thin beam by control grid. (The control grid is also called as Wehnelt cylinder.) So, 2nd option is incorrect.

Which of the following options is TRUE?

  1. X-rays are used in astronomy.

  2. X-rays can penetrate through human flesh.

  3. X-rays can pass through metallic materials.

  4. X-rays are used in optical microscopy.

Show answer
Correct Option: B
Explanation:

X-rays can penetrate through human flesh.

X-rays are produced when

  1. electric current flows through the X-ray tube filament

  2. projectile electrons bounce off the cathode

  3. projectile electrons interact with target atoms

  4. the target angle is sufficiently large

Show answer
Correct Option: C
Explanation:

X-rays are produced when projectile electrons interact with target atoms.

Which of the following is not true for electron gun as a part of hot cathode ray tube?

  1. Cathode C is indirectly heated by filament F.

  2. The anodes are maintained by means of low tension battery with respect to cathode.

  3. The rate of emission of electrons increases from cathode on increasing filament current.

  4. The brightness of pattern on screen varies by changing negative potential on grid.

Show answer
Correct Option: B
Explanation:

In an electron gun, the anodes have a small hole along their axes and they are maintained at a high positive potential with respect to cathode, by means of a high tension battery of about 1000 V. The low tension battery of 6 V is connected by cathode C and filament F. The electrons obtained from cathode are accelerated by a series of cylindrical anodes.

When can a steady bright spot be seen on the screen on the deflecting system in a hot cathode ray tube?

  1. When the electron beam strikes the centre of the screen

  2. When no potential difference is applied across the pairs of plates

  3. When there is no fluorescence on the screen

  4. Both (1) and (2)

Show answer
Correct Option: D
Explanation:

When no potential difference is applied across the pairs of plates, the electrons beam strikes the centre of the screen and a steady bright spot is seen due to fluorescence on the screen on the deflecting system in a hot cathode ray tube.

X-rays are used in

  1. radio therapy to cure tumors

  2. sterilizing surgical instruments

  3. studying the structure of molecules

  4. detecting invisible writings

Show answer
Correct Option: A
Explanation:

X-rays are used in radio therapy to cure tumors.

Which of the following is not an advantage of nuclear energy?

  1. Nuclear fuel can be used for a long time.

  2. It can cause very serious health problems in case of an accident.

  3. Even a small amount of nuclear fuel has the ability to generate very high amount of energy.

  4. It helps to reduce the dependence on fossil fuels.

Show answer
Correct Option: B
Explanation:

Accidents involving nuclear power plants are disastrous and have very grave consequences.

Which of the following statements is/are true?

  1. In nuclear fission, nucleus of a heavy atom, when bombarded with low energy neutrons, can split apart into lighter nuclei.

  2. Tremendous amount of energy is released in a nuclear fission reaction.

  3. Small amount of energy is released in a nuclear fission reaction.

  4. Both (1) and (2)

Show answer
Correct Option: D
Explanation:

Nuclear fission reaction involves the splitting of a big atom into smaller atoms with a tremendous release of energy.

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