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Sub atomic particles short questions

Question 5.1: Which observations tell the presence of cathode rays in the discharge tube?
Answer: Cathode rays produce fluorescence on the striking glass wall opposite to the cathode. Fluorescence is a phenomenon in which a substance absorbs energy and then emits in the form of radiations. The color of the fluorescence produced on the walls of the glass tube, depends upon the composition of glass. When we place the alumina and tin stones in the path of cathode rays, alumina glows red and tin yellow. 

Question 5.2: Why are the cathode rays produced in the discharge tube by applying a high voltage?
Answer: When high voltage of 5000-10000 volts is applied at the pressure of around 0.01 torr, cathode rays are produced. Reason is that at this voltage electrons have enough energy to release from cathode, to overcome the gas pressure of 0.01torr and to reach at anode and strike the glass walls. 

Question 5.3: Why is it necessary to decrease the pressure in the discharge tube to get the cathode rays?
Answer: The pressure in discharged tube is decreased to allow the cathode rays and anode rays to move freely from one electrode to the other. This is because, In this way the possibility of collisions between rays and gas molecules are minimized.

Question 5.4: How various experiments conducted in the cathode rays tube show that cathode rays are material particles with the negative charge on them? 
Answer: In 1897, J. Thomson showed that cathode rays negatively charged because when these rays are passed through the electric field, they are deflected towards the positively charged plate. Similarly, these rays can drive small paddle wheel placed in their path. This shows that these rays possess momentum which means that cathode rays are not rays but material particles with definite velocity and mass. 

Question 5.5: Whichever gas is used in the discharge tube; the nature of the cathode rays remains the same why?
Answer: Atoms or molecules of all gases contain electrons. When cathode rays collide with atoms or molecules of gases in the discharge tube, they knock out only electrons which are attracted towards anode. As cathode rays also consist of electrons and are attracted toward anode, so nature of cathode rays does not change whichever gas is used. 

Question 5.6: Why e/m value of the cathode rays is just equal to that of electrons?Answer: Cathode rays are electrons, so their e/m values are just equal to those of electrons.

Question 5.7: How do electric and magnetic fields show that cathode rays negatively charged?
Answer: The cathode rays are deflected towards the positively charged plate when electric field is applied. It shows that cathode rays are negatively charged. When cathode rays are passed through the magnetic field, they are deflected perpendicular to line joining the north and south pole. This also shows that they are negatively charged because positively charged particles are deflected in opposite direction.

Question 5.8: Why the positive rays are also called canal rays? Give its reasons.
Answer. When pressure inside the discharge tube is reduced and high voltage is applied, cathode rays are produced. When cathode rays are travelling away from cathode, other rays produced at the same time, are travelling towards the cathode. As these rays produce glow on the glass wall after passing through canals or holes of cathodes, they are called canal rays. 

Question 5.9: The e/m values of positive rays for different gases are different but those for cathode rays the e/m values are same. Justify it. 
Answer. When high speed cathode rays strike with molecules of a gas, they knock out the electrons from the gas molecules and positive rays are produced. The charge to mass ratio (e/m) value of positive rays are different for different gases used in discharge tube. As different gases have different positive ions, so their e/m values are also different.As cathode rays also consist of electrons, so charge to mass ratio(e/m) for electrons remain same and do not change whichever gas is used.  

Question 5.10: The value of the positive rays obtained from the hydrogen gas is 1836 times less than that of cathode rays. Justify it.
Answer. When we use hydrogen gas in the discharge tube positive rays consist of protons only. The proton is 1836 times heavier than that of electron. So, its e/m is 1836 times smaller.

Question 5.11: Why the anode rays depend upon the nature of the gas?
Answer. When high speed cathode rays strike with molecules of gas, they knock out the electrons from the gas molecules and positive rays are produced. The charge to mass ratio (e/m) value of positive rays is different for different gases used in discharge tube. Reason is that different gases have different positive ions in discharge tube, therefore their e/m values are also different. Heavier the gas, the smaller the e/m value. 

Question 5.12: How the idea of the proton can be verified by taking H2 gas in the discharge tube?
Answer. As hydrogen nucleus consists of just a proton. Hence the positive ion obtained from the hydrogen gas is called proton and is lightest among all positive particles. In this way when we study anode rays, they give properties of protons.                                                                                                                                      Next

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