(i) Isotope of cobalt, ( Co), is used in the treatment of cancer. For example, Ne has atomic number as 10 and sodium has atomic number as 11 but both of these have mass numbers as 22. (iv) Isobars are such atoms which have same mass number but different atomic numbers. For example, chlorine has two isotopes with atomic number 17 but mass numbers as 35 and 37. (iii) Isotopes are atoms of the same element thus having same atomic number but different mass number. For example there are 6 protons and 6 neutrons in the nucleus of carbon, so its mass number is 12. (ii) Mass number is defined as the sum of the total number of protons and neutrons present in the nucleus of an atom. All atoms are characterized by their atomic numbers. For example, there are 6 protons in carbon, so the atomic number of carbon is 6. (i) Atomic number is defined as number of protons present in the nucleus of an atom. There is a loss or gain in energy of electron when it moves from one orbit to the other. To explain stability of atom and atomic spectra, Bohr suggested that electrons are moving round the nucleus in orbits which have fixed energy shells. This will lead to loss of energy of the moving electron and ultimately giving unstable model of atom. Since charged bodies moving in circular motion emit radiations. Iii)A very small fraction of (a)-particles were deflected by 180 0, indicating that all the positive charge and mass of the gold atom were concentrated in a very small volume with in the atom.ģ.)Neils Bohr. Ii)Very few particles were deflected from their path, indicating that the positive charge of the atom occupies very little space. I)Most of the space inside the atom is empty because most of the (a)-particles passed through the gold foil without getting deflected. On the basis of above experiment Rutherford concluded that: So, the atom as a whole is electrically neutral.Ģ.)Rutherford designed a model in which fast moving alpha (a)-particles were made to fall on a thin gold foil. Ii)The negative and positive charges are equal in magnitude. I)An atom consists of a positively charged sphere and the electrons are embedded in it. On the base of this model Thomson proposed that: In which the positive charge in atom is spread all over like the red edible part of the watermelon, while the electrons are studded in the positively charged sphere, like the seeds in the watermelon. Thomson found that this value comes to \( 1.76 \times 10^8 C/g \).1).Thomson proposed the model of an atom to be similar to that of a watermelon. The charge-to-mass ratio of the electron can be determined by measuring the effects of the magnetic and electric fields on the motion of the beam.What is the charge-to-mass ratio for the cathode ray particles?.If the correct combination is reached, the can completely cancel each other out and not deflect the rays at all. When both electric and magnetic forces are applied to the cathode ray, they combine against or with each other to deflect the cathode rays.What is the effect of simultaneous electric and magnetic fields on the cathode ray?.Again, this is due to the negative charge the cathode rays possess. When the north pole is facing towards the CTR, the beam is deflected upwards. If the south pole is facing towards the CTR (Cathode Ray Tube), the beam is deflected down. When a magnetic field is applied, the cathode rays get deflected.What is the effect of a magnetic field on the cathode ray?.This is because the cathode rays are negatively charged. When an electric field is applied to a stream of cathode rays, they are deflected towards the positive plate.What is the effect of an electric field on the cathode ray?.Notice the dotted circle indicating the position of the coils, the direction of the magnetic field between the coils and the value of the field. In the Thomson applet, set the voltage at 0 V and move the slider for the current to the right. When a current flows through the coils, a uniform magnetic field is created in the region between the horizontal plates. Using the same tube as shown in Figure 1 (above), he placed a pair of coils outside of the tube and on either side of the horizontal plates (Figure 3, below). Thomson also used a magnetic field to affect the beam of cathode rays. In the Thomson applet, this angle is provided by selecting Deflection Angle in the Options menu. From measurements of this deflection, he was able to calculate the angle of deflection. Thomson measured the deflection of the beam using a ruler etched on the end of the tube. You can see a simulation of this glow on the far right of the applet diagram, as shown in Figure 2. In Thomson’s experiment, a fluorescent material was coated on the end of the tube to produce a glowing dot where the cathode rays hit.
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