Sunday, September 25, 2022

H C Verma solutions, ELECTRIC CURRENT THROUGH GASES, Chapter-41, OBJECTIVE-I, Concepts of Physics, Part-II

Electric Current Through Gases


OBJECTIVE-I


     1.  Cathode rays constitute a stream of 

(a) electrons

(b) protons

(c) positive ions

(d) negative ions. 


ANSWER: (a).   


EXPLANATION: The cathode is connected to the negative terminal of the source. When a high potential difference is applied across the discharge tube, free electrons increase on the cathode, and at very low pressure in the tube, a beam of electrons rushes from the cathode toward the anode. This beam is called a cathode ray.     




     2.  Cathode rays are passing through a discharge tube. In the tube, there is 

(a) an electric field but no magnetic field

(b) a magnetic field but no electric field

(c) an electric as well as a magnetic field

(d) neither an electric field nor a magnetic field.   


ANSWER: (c).   


EXPLANATION: Cathode rays are itself a result of a high electric field present in the discharge tube. Also, cathode rays are beams of fast-moving electrons that also ionize gas molecules present in the tube. These charged particles have also their electric fields around them. Since a moving charged particle also produces a magnetic field around it, there is also a magnetic field present in the tube. 



        



     3.  Let iₒ be the thermionic current from a metal surface when the absolute temperature of the surface is Tₒ. The temperature is slowly increased and the thermionic current is measured as a function of temperature. Which of the following plots may represent the variation in (i/iₒ) against (T/Tₒ). 
The figure for Q-3


ANSWER: (d).   


EXPLANATION: From the Richardson-Dushman equation, the thermionic current is directly proportional to the square of the absolute temperature and directly proportional to e-φ/kT. Hence the current will increase exponentially with an increase in temperature and only plot (d) relates to it.     



     4.  When the diode shows the saturated current, dynamic plate resistance is

(a) zero

(b) infinity

(c) indeterminate

(d) different for different diodes.   


ANSWER: (b).   


EXPLANATION: Dynamic plate resistance is the ratio of the change in plate voltage to the corresponding change in the current. Since at saturation, there is no increase in current with an increase in plate voltage, the dynamic plate resistance becomes infinity. 



    



     5.  The anode of a thermionic diode is connected to the negative terminal of a battery and the cathode to its positive terminal.

(a) No appreciable current will pass through the diode.

(b) A large current will pass through the diode from the anode to the cathode.

(c) A large current will pass through the diode from the cathode to the anode.

(d) The diode will be damaged. 


ANSWER: (a).   


EXPLANATION: In this case, the electrons are pushed back towards the cathode, and no current flows in the external circuit. Hence option (a). 



    



     6.  A diode, a resistor, and a 50 Hz AC source are connected in series. The number of current pulses per second through the resistor is 

(a) 25

(b) 50

(c) 100

(d) 200. 


ANSWER: (b).   


EXPLANATION: Since the diode will allow current only in one direction, only half cycle of a cycle of AC source will show current as a current pulse. Hence the number of current pulses per second will be equal to the frequency of the AC source. Option (b) is correct. 


       



     7.  A triode is operated in the linear region of its characteristics. If the plate voltage is slightly increased, the dynamic plate resistance will

(a) increase

(b) decrease

(c) remain almost the same

(d) become zero. 


ANSWER: (c).   


EXPLANATION: The dynamic plate resistance 

rₚ =ΔVₚ/Δiₚ

In the linear region of the triode characteristic, ΔVₚ ≈ Δiₚ, hence rₚ will remain almost the same. 




      



     8.  The plate current in a triode valve is maximum when the potential of the grid is

(a) positive

(b) zero

(c) negative

(d) nonpositive. 


ANSWER: (a).   


EXPLANATION: When the potential of the grid is made positive, it helps electrons emitted from the cathode to accelerate towards the plate. Thus increasing the current. Hence option (a) is correct. 



    



     9.  The amplification factor of a triode operating in the linear region depends strongly on

(a) the temperature of the cathode

(b) the plate potential

(c) the grid potential

(d) the separations of the grid from the cathode and the anode. 


ANSWER: (d).   


EXPLANATION: When the triode is operating in the linear region of its characteristics, the plate voltage, grid voltage, and temperature of the cathode are already specified. It is the separation of the grid from the cathode or the anode that affects the amplification factor. If the grid is nearer to the cathode, the electrons are accelerated strongly. Option (d) is correct.    


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Links to the Chapters




CHAPTER- 41- Electric Current Through Gases



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".

---------------------------------------------------------------------------------

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)

-------------------------------------------------------------------------------

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


--------------------------------------------------------------------------------------------------------------

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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