Home
Class 12
PHYSICS
The mean free path of electrons in the g...

The mean free path of electrons in the gas in a discharge tube is inversely proportional to the pressure inside it. The Crookes dark space occupies half the length of the discharge tube when the pressure is `0.02 mm` of mercury. Estimate the pressure at which the dark space will fill the whole tube.

Text Solution

Verified by Experts

Let the mean free path be'L' and pressure
be 'P'
Given L `alpha 1/p for L ` = half on the tube length `
` P = 0.02mm of Hg.`
` As 'P' becomes half, 'L' doubles, that is the
whole tube is filled with Crook's dark
space.
Hence the required pressure
= 0.02 /2 = 0.01 m of Hg .
Promotional Banner

Topper's Solved these Questions

  • ELECTRIC CURRENT THROUGH GASES

    HC VERMA|Exercise Objective 2|7 Videos

  • ELECTRIC CURRENT IN CONDUCTORS

    HC VERMA|Exercise Exercises|84 Videos

  • ELECTRIC FIELD AND POTENTIAL

    HC VERMA|Exercise Exercises|75 Videos

Similar Questions

Explore conceptually related problems

Colour in discharge tube filled with gas at low pressure is due to …

An ideal gas in enclosed in a tube and is held in the vertical position with the closed end upward. The length of pellet of mercury entrapping the gas is h = 10 cm and the length of the tube occupied by gas is l=40 cm. Calculate the length occupied by the gas when it is turned through theta= 60^(@) and 90^(@) . Atmospheric pressure , H= 76 cm of mercury.

A thin tube of uniform cross-section is sealed at both ends. It lies horizontally, the middle 5 cm containing mercury and the two equal end containing air at the same pressure P. When the tube is held at an angle of 60^@ with the vetical direction, the length of the air column above and below the mercury column are 46 cm and 44.5 cm respectively. Calculate the pressure P in centimeters of mercury. (The temperature of the system is kept at 30^@C ).

A horizontal cylinderical tank (6)/(pi)m in diameter is half full of water. The space above the water is filled with a pressurized gas of unknown refractive index. A small laser can move along the curved bottom of the water and aims a light beam towards the centre of the water surface. When the laser has moved a distance s=1m or more (measured from curved face) from the lowest point in water, no light enters the gas. The refractive index of gas is (mu_("water") = 4//3)

A potato gun first a potato horizontally down a half-open cylinder of cross-sectional area A . When the gun is fired , the potato slug is at rest , the volume betweeen the end of the cylinder and the potato is V_(0) , and the pressure of the gas in this volume is P_(0) . The atmospheric pressure is P_("atm") . where P__(0) gt P_("atm") . The gas in the cylinder is diatomic, this means that C_(V) = (5R)/(2) and C_(P) = (7R)/(2) . The potato moves down the cylinder quickly enough that no heat is transferred to the gas. Friction between the potato and the barreel is negligible and no gas leaks around the potato . The parameters P_(0) , P_("atm"), V_(0) and A are fixed, but the overall length L of the barrel may be varied. The length L in this case is

A potato gun first a potato horizontally down a half-open cylinder of cross-sectional area A . When the gun is fired , the potato slug is at rest , the volume betweeen the end of the cylinder and the potato is V_(0) , and the pressure of the gas in this volume is P_(0) . The atmospheric pressure is P_("atm") . where P__(0) gt P_("atm") . The gas in the cylinder is diatomic, this means that C_(V) = (5R)/(2) and C_(P) = (7R)/(2) . The potato moves down the cylinder quickly enough that no heat is transferred to the gas. Friction between the potato and the barreel is negligible and no gas leaks around the potato . The parameters P_(0) , P_("atm"), V_(0) and A are fixed, but the overall length L of the barrel may be varied. The maximum kinetic energy E_("max") with which the potato can exit the barrel?

Two glass bulbs of equal volume are connected by a narrow tube and are filled with a gas at 0^@C and a pressure of 76cm of mercury. One of the bulbs is then placed in melting ice and the other is placed in a water bath maintained at 62^@C . What is the new value of the pressure inside the bulbs? The volume of the connecting tube is negligible.

A container having base area A_(0) . Contains mercury upto a height l_(0) . At its bottom a thin tube of length 4l_(0) and cross-section area A(AltltA_(0) ) having lower end closed is attached . Initially the length of mercury in tube is 3l_(0) . in reamining part 2 mole of a gas at temperature T is closed as shown in figure . Determine the work done (in joule) by gas if all mercury is displaced from tube by heating slowly the gas in the rear end of the tube by means of a heater. (Given : density of mercury = rho , atmospheric pressure P_(0) = 2l_(0)rhog, C_(v) of gas = 3//2 R, A = (3//rho)m^(2), l_(0) = (1//9) m , all units is S.I. )

An electron gun with its collector at a potential of 100 v fires out electrons in a spherical bulb containing hydrogen gas at low pressure (~10^(-2)" mm of Hg") . A magnetic field of 2.83 xx 10^(-4) T curves the path of the electrons in a circular orbit of radius 12.0 cm. (The path can be viewed because the gas ions in the path focus the beam by attracting electrons, and emitting light by electron capture, this method is known as the ‘fine beam tube’ method.) Determine e/m from the data.

HC VERMA-ELECTRIC CURRENT THROUGH GASES-Exercises
  1. A discharge tube contains helium at a low pressure. A large potential ...

    Text Solution

    |

  2. A molecule of a gas, filled in a discharge tube, gets ionized when an ...

    Text Solution

    |

  3. The mean free path of electrons in the gas in a discharge tube is inve...

    Text Solution

    |

  4. Two discharge tubes have identical material structure and the same gas...

    Text Solution

    |

  5. Calcuate n(T)//n (1000 K) for tungsten emitter at T = 300 K, 2000 K an...

    Text Solution

    |

  6. The saturation current from a thoriated-tungsten cathode at 2000 K is ...

    Text Solution

    |

  7. A Tungsten cathode and a thoriated-tungsten cathode have the same geom...

    Text Solution

    |

  8. If the temperature of a tungsten filament is raised from 2000 K to 201...

    Text Solution

    |

  9. The constant A in the Richardson-Dushman equation for tungsten is 60 x...

    Text Solution

    |

  10. A plate current of 10 mA is obtained when 60 volts are applied across ...

    Text Solution

    |

  11. The plate current in a diode is 20 mA when the plate voltage is 50 V o...

    Text Solution

    |

  12. The power delivered in the plate circuit of a diode is 1.0 W when the ...

    Text Solution

    |

  13. A triode valve operates at Vp = 225 V and Vg = - 0.5 V. The plate curr...

    Text Solution

    |

  14. Calculate the amplification factor of a triode valve which has plate r...

    Text Solution

    |

  15. The dynamic plate resistance of a triode valve is 10 kOmega. Find the ...

    Text Solution

    |

  16. Find the values of rp, mu and gm of a triode operating at plate voltag...

    Text Solution

    |

  17. The plate resistance of a triode is 8 kOmega and the transconductiance...

    Text Solution

    |

  18. The plate resistance and the amplification factor of a triode are 10 k...

    Text Solution

    |

  19. The plate current, plate voltage and grid voltage of a 6F6 triode tube...

    Text Solution

    |

  20. The plate current in a triode can be written as ip = k ((Vg + (Vp)/(...

    Text Solution

    |