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PHYSICS- Laws of Motion

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When the cathode is heated from the 6.3 V AC supply, electrons are emitted from its surface. These electrons fall on the grid (which is positive) and a current flows in the cathode/grid circuit. As electrons stream from the cathode toward the grid, they bombard atoms of the gas under study (in this case a noble gas) inside the valve. As the potential difference between the cathode and the grid is increased, electrons are accelerated through the valve at greater and greater speeds. As the kinetic energy of the electrons continues to increase, it eventually becomes great enough such that on collision with an atom, the most loosely bound electron is removed from the atom to yield a cation. The cations are attracted to the negative terminal and the electrons to the positive terminal and this leads to a sudden increase in the reading from the ammeter. The kinetic energy of the bombarding electrons can be calculated from the voltage of the system via the following formula:

How does the force exerted on the cations relate to the force exerted on the electrons given that the mass of the cation involved is 6.7 x 10-27 kg ?
AND is this a circuit + electrostatics problem? why is it causing the same force on both the cation and electron?


  • PHYSICS- Laws of Motion -

    During the collision between electron and atom, the electron exerts a force on the atom and the atom exerts an equal and opposite force on the electron. That is Newton's third law.

    The rest of the problem is about the energy required to free a bound electron from its orbit about the atom forming a positive ion flowing toward the cathode and another electron in the stream flowing toward the grid.

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