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Chapter 29: Q21CQ (page 1062)
Why don鈥檛 we feel the momentum of sunlight when we are on the beach?
As Plank's constant is too small so when we calculate the momentum of the photon it will be very tiny amount. So, it's so small to be noticed.
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Question: Red light having a wavelength of \({\rm{700 nm}}\) is projected onto magnesium metal to which electrons are bound by \({\rm{3}}{\rm{.68 eV}}\). (a) Use \({\rm{KEe = hf-- BE}}\) to calculate the kinetic energy of the ejected electrons. (b) What is unreasonable about this result? (c) Which assumptions are unreasonable or inconsistent?
Question: (a) Find the energy in joules and eV of photons in radio waves from an FM station that has a \({\rm{90}}{\rm{.0 - MHz}}\) broadcast frequency. (b) What does this imply about the number of photons per second that the radio station must broadcast?
(a) How far away must you be from a \({\bf{650 - kHz}}\) radio station with power \({\bf{50}}{\bf{.0 kW}}\) for there to be only one photon per second per square meter? Assume no reflections or absorption, as if you were in deep outer space.
(b) Discuss the implications for detecting intelligent life in other solar systems by detecting their radio broadcasts.
The velocity of a proton emerging from a Van de Graaff accelerator is 25% of the speed of light. (a) What is the proton鈥檚 wavelength?
(b) What is its kinetic energy, assuming it is nonrelativistic?
(c) What was the equivalent voltage through which it was accelerated?
(a) Calculate the number of photoelectrons per second ejected from a \(1.00\,{\rm{m}}{{\rm{m}}^{\rm{2}}}\) area of sodium metal by \(500\,{\rm{nm EM}}\) radiation having an intensity of \(1.30\,{\rm{kW/}}{{\rm{m}}^{\rm{2}}}\) (the intensity of sunlight above the Earth鈥檚 atmosphere). (b) Given that the binding energy is\(2.28\,{\rm{eV}}\), what power is carried away by the electrons? (c) The electrons carry away less power than brought in by the photons. Where does the other power go? How can it be recovered?
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