A brass plate at room temperature radiates 10 W of blackbody radiation. If the plate is cooled to –30°C, does the peak of maximum radiated intensity shift toward shorter wavelengths, shift toward longer wavelengths, or remain the same? Explain.

1. Summarize the experimental evidence prior to the research of Thomson by which you might conclude that cathode rays are some kind of particle.

2. Summarize the experimental evidence prior to the research of Thomson by which you might conclude that cathode rays are some kind of wave.

Thomson observed deflection of the cathode-ray particles due to magnetic and electric fields, but there was no observed deflection due to gravity. Why not?

What was the significance of Thomson’s experiment in which an off-center electrode was used to collect charge deflected by a magnetic field?

What is the evidence by which we know that an electron from an iron atom is identical to an electron from a copper atom?

FIGURE Q37.6 shows a magnetic field between two parallel, charged electrodes. An electron with speed $v_0$ passes between the plates, from left to right, with no deflection. If a proton is fired toward the plates with the same speed $v_0$, will it be deflected up, deflected down, or pass through with no deflection? Explain.

FIGURE Q37.6

1. Describe the experimental evidence by which we know that the nucleus is made up not just of protons.

2. The neutron is not easy to isolate or control because it has no charge that would allow scientists to manipulate it. What evidence allowed scientists to determine that the mass of the neutron is almost the same as the mass of a proton?

Rutherford studied alpha particles using the crossed-field technique Thomson had invented to study cathode rays. Assuming that $v_{\text{alpha}}\approx v_{\text{cathode ray}}$ (which turns out to be true), would the deflection of an alpha particle by a magnetic field be larger than, smaller than, or the same as the deflection of a cathode-ray particle by the same field? Explain.

Once Thomson showed that atoms consist of very light negative electrons and a much more massive positive charge, why didn’t physicists immediately consider a solar-system model of electrons orbiting a positive nucleus? Why would physicists in 1900 object to such a model?

Explain why the observation of alpha particles scattered at very large angles led Rutherford to reject Thomson’s model of the atom and to propose a nuclear model.

An alpha particle (a bare helium nucleus with $q=+2e$) accelerates across a 100 V potential difference, starting from rest. What is the particle’s kinetic energy in eV when it reaches the negative electrode? This question requires no mathematics beyond what you can do in your head.

Identify the element, the isotope, and the charge state of each atom in FIGURE Q37.12. Give your answer in symbolic form, such as ${}^4{\text{He}}^{+}{\text{or }}^8{\text{Be}}^{-}$.

FIGURE Q37.12

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