Concept explainers
The experimental evidence that convinced Thomson that he had discovered a subatomic particle, while working with cathode rays.
Answer to Problem 1CQ
While discovering cathode rays, J.J. Thomson observed deflection of cathode rays in between charged metal plates. After observing these all Thomson concludes that the electrons are fundamental particle of matter and he called them as sub atomic particle.
Explanation of Solution
While discovering cathode rays, J.J. Thomson observed deflection of cathode rays in between charged metal plates. As the law of charges if the charges characteristic are same then they repel each other and when the charges characteristic are different then they attract each other.
The cathode rays are negatively charged particles and deflected in the combination of the electric and magnetic fields. After observing that the invariance of the ratio of charge to mass Thomson concluded that the electrons are a fundamental particle of a matter and it is true no matter what the conditions under which he measured the ratio. So he called them as a subatomic particle.
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Chapter 8 Solutions
Integrated Science
- A Thomson-type experiment with relativistic electrons. One of the earliest experiments to show that p = mv (rather than p = mv) was that of Neumann. [G. Neumann, Ann. Physik 45:529 (1914)]. The apparatus shown in Figure P4.5 is identical to Thomsons except that the source of high-speed electrons is a radioactive radium source and the magnetic field B is arranged to act on the electron over its entire trajectory from source to detector. The combined electric and magnetic fields act as a velocity selector, only passing electrons with speed v, where v = V/Bd (Equation 4.6), while in the region where there is only a magnetic field the electron moves in a circle of radius r, with r given by p = Bre. This latter region (E = 0, B = constant) acts as a momentum selector because electrons with larger momenta have paths with larger radii. (a) Show that the radius of the circle described by the electron is given by r = (l2 + y2)/2y. (b) Typical values for the Neumann experiment were d = 2.51 104 m, B = 0.0177 T, and l = 0.0247 m. For V = 1060 V, y, the most critical value, was measured to be 0.0024 0.0005 m. Show that these values disagree with the y value calculated from p = mv but agree with the y value calculated from p = mv within experimental error. (Hint: Find v from Equation 4.6, use mv = Bre or mv = Bre to find r, and use r to find y.) Figure P4.5 The Neumann apparatus.arrow_forwardThe Balmer series for hydrogen was discovered before either the Lyman or the Paschen series. Why?arrow_forwardShow that Planck’s constant has the dimensions of angular momentum.arrow_forward
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- The gravitational attraction between electron and proton in a hydrogen atom is weaker than the coulomb attraction by a factor of about 10-40. An alternative way of looking at this fact is to estimate the radius of the first Bohr orbit of a hydrogen atom if the electron and proton were bound by gravitational attraction. You will find the answer interesting.arrow_forwardSuppose an electron was bound to a proton, as in thehydrogen atom, but by the gravitational force rather thanby the electric force. What would be the radius, and energy,of the first Bohr orbit?arrow_forwardThomson himself was perhaps the biggest critic of the model referred to as “plum pudding.” He tried for years to make it work. What experimental data could he not predict? Why couldn’t he make the planetary model of Rutherford-Bohr work?arrow_forward
- Why did only some of the a-particles bounce back when Ernest Rutherford fires the a-particles at a thin film of gold foil?arrow_forwardThe kinetic energy of an electron in a particular Bohr orbit is 135 10 19 . × . − J (a) Which Bohr orbit does theelectron occupy? (b) Suppose the electron moves away from the nucleus to the next higher Bohr orbit. Does thekinetic energy of the electron increase, decrease, or stay the same? Explain. (c) Calculate the kinetic energy ofthe electron in the orbit referred to in part (b)arrow_forwardWhy is the classical (Rutherford) model for an atom—of electron orbitting around the nucleus—not able to explain the atomic structure?arrow_forward
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