Edexcel A-Level Physics Electronvolt

Practise Edexcel A-Level Physics electronvolt conversions with electron energy changes, potential difference and atomic energy calculations.

Exam points

define 1 eV as the energy change for an electron accelerated through 1 volt
convert calculated atomic energies from joules into eV using 1.60 × 10⁻¹⁹ J per eV

[Maximum number: 3]

Niels Bohr developed an early model of the atom where electrons could only exist in fixed orbits around a nucleus. When an atom is ionised, an electron moves from its orbit around the nucleus to be free of the atom. Bohr derived an expression for the ionisation energy E, in joules, for a hydrogen atom:

$\left(\frac{e^2}{kh}\right)^2\times\frac{m}{8}$

where m is the mass of the electron, e is the charge of the electron, $k=8.85\times10^{-12}\,\mathrm{C\,V^{-1}m^{-1}}$ , and h is the Planck constant.

Calculate E for a hydrogen atom, in eV.
(3)

E=\ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots . \mathrm{eV}

Substitute the constants into $E=\left(\frac{e^2}{kh}\right)^2\frac{m}{8}$ to obtain $E=2.17\times10^{-18}\,\mathrm{J}$ . Divide by $1.60\times10^{-19}\,\mathrm{J\,eV^{-1}}$ to give $13.56\,\mathrm{eV}$ (13.5 or 13.6 eV).

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2.3.61 - Electronvolt question 1