By decreasing the pressure in the discharge tube the no. of gas molecules also reduce. Due to less no. of molecules, the hindrance in the movement of electron also reduces. So, cathode rays only produce at low pressure.
02. Whichever gas is used in the discharge tube the nature of cathode rays is the same. Why?
Cathode rays are basically electrons. Electrons are the fundamental particle of matter. Every matter has an electron of identical nature. So, cathode rays have the same nature for every gas.
03. Why the e/m value of the cathode rays is just equal to that of electrons?
The e/m value of the cathode rays is just equal to that of electrons because cathode rays are actually electrons i. e. 1.7588 × 1011C kg−.
04. How the bending of cathode rays in the electrically and magnetic field shows that they are electrons?
In the magnetic field, cathode rays are deflected perpendicular to the line joining the two poles of the magnetic field.
In the electrical field, these rays deflected towards a positive plate which shows that they have negative charge on them.
05. Why positive rays are also called canal rays?
Small openings in the cathode called canals. Positive rays pass through these canals and produce a glow on sticking the wall of the discharge tube. That is why they are called canal rays.
06. The e/m value for positive rays is different for different gases but that of cathode rays is the same. Explain.
Cathode rays are electrons that are similar in nature for all the gases. But positive rays are positive ions of the gas used in the discharge tube. All the gases have different mass so the e/m value is different for different gases. Hydrogen is the lightest gas so it has the highest e/m value.
07. The e/m value for positive rays obtained for hydrogen is 1836 times less than that of cathode rays. Explain.
The mass of an electron is very small than that of proton or hydrogen positive rays. The mass of the proton is almost 1836 times greater than that of the electron. The value of e/m is inversely related to the mass.
08. The potential energy of the bonded electron is negative. Explain.
The free-electron has no attraction with the nucleus and considered to be at infinite distance from the nucleus. So its potential energy is zero. When the electron comes closer to the nucleus its potential energy decreases which are represented by the negative sign.
09. The total energy of the electron is also negative. Explain.
The total energy of the electron is the sum of potential and kinetic energy. Kinetic energy is positive but potential energy is negative. When both energies are added, the total energy becomes negative.
10. The energy of an electron is inversely proportional to n 2, but the energy of higher orbits is always greater than those of the lower orbits.
According to the energy equation of Bohr’s model, the Energy of an electron is inversely proportional to n2. Greater will be the value of n greater will be the energy because it has negative sing. Hence energy increases by increasing n and its maximum value are zero when n is equal to infinity.
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