a) [2018] State Kirchhoff’s two Laws, and give the fundamental physical principles which each law expresses.
b) De Broglie explained the
a particle, with the value of λ coming from the momentum p = mv as λ = h/p.
i) Calculate the de Broglie wavelength of a bird (a racing pigeon) that weighs 0.350 kg
and flies at 100 km per hour.
ii) Equating the
iii) Calculate the momentum and the de Broglie wavelength of an electron moving at the speed you obtain in (ii).
iv) Compare the wavelength you obtain in (iii) with the circumference of the orbit. Com- ment on this comparison. Explain briefly what it implies about the possible orbits of the Bohr model and how the higher orbits might be predicted.
c) Thorium-234 is a radioactive element that has a decay constant of 3.33×10−7 s−1. It decays by beta-decay with an energy of 270 keV. A sample of pure Th-234 has an initial activity of 8.56 × 1013 Bq.
i) Calculate the initial number of atoms present.
ii) Calculate number of days taken for the activity to drop to one-sixteenth of the initial
activity.
iii) Calculate the initial mass of the sample, and estimate the reduction in mass at the time calculated in (ii).
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