Problems are listed in approximate order of difficulty. A single dot (•) indicates straightforward problems involving just one main concept and sometimes requiring no more than substitution of numbers in the appropriate formula. Two dots (••) identify problems that are slightly more challenging and usually involve more than one concept. Three dots (•••) indicate problems that are distinctly more challenging, either because they are intrinsically difficult or involve lengthy calculations. Needless to say, these distinctions are hard to draw and are only approximate.
• A student doing the Rutherford scattering experiment arranges matters so that she gets 80 counts/min at a scattering angle of θ = 10°. If she now moves her detector around to θ = 150°, keeping it at the same distance from the target, how many counts would she expect to observe in a minute? (This illustrates an awkward feature of the experiment, especially before the days of automatic counters. An arrangement that gives a reasonable counting rate at small θ gives far too few counts at large θ, and one that gives a reasonable rate for large θ will overwhelm the counter at small θ.)
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