Bohr's postulates and his derived rₙ, vₙ and Eₙ, the five spectral series in one table, de Broglie's λ = h/p and the uncertainty principle, and the X-ray spectrum with Bragg's law.
Unit 6 carries 12 of the 50 physics marks — more than any other physics unit — and with seven chapters sharing them this one averages a little under two (MEC publishes weights by unit, not by chapter). It is also the widest chapter in the whole subject: it runs from why hydrogen glows red, through why an electron can diffract, to what happens inside the tube that takes a chest radiograph.
The MEC scope lines are: Bohr's theory of the hydrogen atom: spectral series and energy levels; de Broglie waves and the uncertainty principle; Production, properties and uses of X-rays; Bragg's law. The three headings below are those three points, in MEC's order.
Three ways it is asked: recall (Bohr's postulates, which series lies in which region of the spectrum, the parts of a Coolidge tube, the properties of X-rays, Bragg's equation); understanding (why the Balmer series alone is visible, why the short-wavelength cut-off depends on the tube voltage but the characteristic lines do not, why a cricket ball has no observable wavelength, what the limitations of Bohr's model are); application (a wavelength from a named transition, rₙ or vₙ or Eₙ for a given n, λ = 12.27/√V for an accelerated electron, λ_min from a kilovoltage, a lattice spacing from a Bragg angle, an uncertainty estimate).
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