Monday, April 24, 2023

H C Verma solutions, X-rays, Chapter-44, Questions for Short Answer, Concepts of Physics, Part-II

X - rays

Questions for Short Answer

      1.  When a Coolidge tube is operated for some time it becomes hot. Where does the heat come from?  

ANSWER: In the Coolidge tube, electrons from the hot filament are accelerated to hit the metal target to emit the X-rays but not all the electrons are able to emit X-rays. Some electrons collide with metal atoms and lose their kinetic energy. The kinetic energy of these absorbed electrons is utilized to increase the vibration of the metal molecules. It increases the temperature of the metal. So the heat in the Coolidge tube comes from the conversion of the kinetic energy of the electrons.      





      2.  In a Coolidge tube, electrons strike the target and stop inside it. Does the target get more and more negatively charged as time passes?   

ANSWER: The target is not an isolated piece of metal but connected to the positive end of a battery terminal to create a large potential difference between the hot filament and the target to accelerate the electrons emitted from the filament. Thus, those electrons that stop inside the target do not remain inside it but go through the outer circuit into the battery. So the target does not get more and more negatively charged with time.      



      3.  Can X-rays be used for the photoelectric effect?  

ANSWER: Of course. If the energy of the X-ray photon is more than the threshold frequency of the metal it can eject photoelectrons from that metal surface.      



      4.  Can X-rays be polarized?  

ANSWER: Since X-rays are also electromagnetic waves, they are transverse in nature. Since transverse waves can be polarised, X-rays can also be polarised. If we consider the particle nature of the light that consists of photons, the polarization can be explained through quantum theory.      




 

      5.  X-ray and visible light travel at the same speed in a vacuum. Do they travel at the same speed in the glass?  

ANSWER: The refractive index of glass for X-rays is less than that for visible light. Since the speed of an electromagnetic wave is inversely proportional to the refractive index, the speed of X-rays in the glass will be more than the visible light.   



  



      6. Characteristic X-rays may be used to identify the element from which they are coming. Can continuous X-rays be used for this purpose?  

ANSWER: Characteristic X-rays are produced when the accelerated electrons knock out an inner electron from the atom of the target. This vacancy is filled by the higher-orbit electrons in the atom. The difference in the energy levels of these two orbits is given to the emitted photon of the X-ray. This difference is characteristic of a particular element. By studying these characteristic X-rays the element can be identified from which they are emitted. 

   Continuous X-rays are emitted when the accelerated electrons lose their kinetic energy after hitting the target and stop inside the target after many collisions. So the energy (and frequency) of the photons thus emitted depends upon the amount of lost kinetic energy of electrons. It does not carry any information about the elements from which they are emitted. So continuous X-rays can not be used for identifying elements from which they are emitted.

 



   



      7.  Is it possible that in a Coolidge tube characteristic Lₐ X -rays are emitted but not Kₐ rays?  

ANSWER: Kₐ X-ray is emitted when an electron in the K shell of the target atom is knocked out by the accelerating electron in the Coolidge tube and the electron in the L shell fills it. But the Lₐ X-ray is emitted if an electron in the L shell is knocked out and it is filled by an M shell electron in the target atom. We know that it requires less energy to knock out an electron from the L shell than the K shell. If the potential difference in the X-ray tube is maintained such that it gives the accelerating electrons less energy than required for dislodging a K shell electron but more energy than required to dislodge an electron from the L shell, then Lₐ X-rays may be emitted but not Kₐ X-rays. Hence in a Coolidge tube, it is possible that only Lₐ X-rays or other L series X-rays are emitted and not the Kₐ X-rays by controlling the potential difference in the tube. 




  



      8.  Can Lₐ X-ray of one material have a shorter wavelength than Kₐ X-ray of another?  

ANSWER: In other words, can an Lₐ X-ray photon of one material have more energy than a Kₐ X-ray photon of another material. The energy levels of K, L, and M shells depend on the atomic number Z of an element. The energy of the photon of Lₐ X-ray is the difference between the L and M shell of the atom while the energy of the photon of Kₐ X-ray is the difference between the K shell and L shell of the atom. There may be a situation in which an element with a higher atomic number such as Z =74 (Tungston) has an energy difference between the L and M shell more than the energy difference between the K and L shell of an element with a lower atomic number say Z =27 (Cobalt). In such a case, Lₐ X-rays of Tungston will have a shorter wavelength than the Kₐ X-rays of Cobalt.



 



      9.  Can a hydrogen atom emit characteristic X-rays?  

ANSWER: The maximum energy of radiation that may be emitted from a hydrogen atom is 13.6 eV while the minimum energy of X-rays is 100 eV. So a hydrogen atom can not emit characteristic X-rays. 



      



      10.  Why is exposure to X-ray injurious to health but exposure to visible light is not, when both are electromagnetic waves?  

ANSWER: It is due to the fact that the photons of X-rays have much more energy than the photons of visible light. With very high frequency, X-rays have much penetrating power with damaging effects on living cells. Long exposures may cause cancer, alter the DNA of cells, and genetic defects.  

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Links to the Chapters





CHAPTER- 34- Magnetic Field

CHAPTER- 29- Electric Field and Potential











CHAPTER- 28- Heat Transfer

OBJECTIVE -I







EXERCISES - Q51 to Q55


CHAPTER- 27-Specific Heat Capacities of Gases

CHAPTER- 26-Laws of Thermodynamics


CHAPTER- 25-CALORIMETRY

Questions for Short Answer

OBJECTIVE-I

OBJECTIVE-II


EXERCISES - Q-11 to Q-18


CHAPTER- 24-Kinetic Theory of Gases







CHAPTER- 23 - Heat and Temperature






CHAPTER- 17 - Light Waves




CHAPTER- 14 - Fluid Mechanics




CHAPTER- 13 - Fluid Mechanics


CHAPTER- 12 - Simple Harmonic Motion









CHAPTER- 11 - Gravitation





CHAPTER- 10 - Rotational Mechanics






CHAPTER- 9 - Center of Mass, Linear Momentum, Collision


CHAPTER- 8 - Work and Energy

Click here for → Question for Short Answers

Click here for → OBJECTIVE-I

Click here for → OBJECTIVE-II

Click here for → Exercises (1-10)

Click here for → Exercises (11-20)

Click here for → Exercises (21-30)

Click here for → Exercises (31-42)

Click here for → Exercise(43-54)

CHAPTER- 7 - Circular Motion

Click here for → Questions for Short Answer 

Click here for → OBJECTIVE-I

Click here for → OBJECTIVE-II

Click here for → EXERCISES (1-10)

Click here for → EXERCISES (11-20)

Click here for → EXERCISES (21-30)

CHAPTER- 6 - Friction

Click here for → Questions for Short Answer

Click here for → OBJECTIVE-I

Click here for → Friction - OBJECTIVE-II

Click here for → EXERCISES (1-10)

Click here for → Exercises (11-20)

Click here for → EXERCISES (21-31)

For more practice on problems on friction solve these- "New Questions on Friction".

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CHAPTER- 5 - Newton's Laws of Motion


Click here for → QUESTIONS FOR SHORT ANSWER

Click here for→Newton's Laws of Motion,Exercises(Q.No. 13 to 27)

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CHAPTER- 4 - The Forces

The Forces-

"Questions for short Answers"    


Click here for "The Forces" - OBJECTIVE-I


Click here for "The Forces" - OBJECTIVE-II


Click here for "The Forces" - Exercises


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CHAPTER- 3 - Kinematics - Rest and Motion

Click here for "Questions for short Answers"


Click here for "OBJECTIVE-I"


Click here for EXERCISES (Question number 1 to 10)


Click here for EXERCISES (Question number 11 to 20)


Click here for EXERCISES (Question number 21 to 30)


Click here for EXERCISES (Question number 31 to 40)


Click here for EXERCISES (Question number 41 to 52)


CHAPTER- 2 - "Physics and Mathematics"

Click here for "Questions for Short Answers"


Click here for "OBJECTIVE-II"

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