Atomic spectra test with answers for A Level physics (free PDF download)

Quick answer: Atoms have discrete energy levels, so an electron changing level emits or absorbs a photon whose energy equals the gap between the levels. This Physics 11-12 test on atomic spectra has 8 questions worth 20 marks, to do in 45 minutes: the electronvolt, reading a level diagram and discrete emission. The mark scheme is on a separate page; free printable PDF.

Answer all the questions. Show each step of a calculation, give units, and use h = 6.63 × 10⁻³⁴ J s, c = 3.00 × 10⁸ m/s, 1 eV = 1.60 × 10⁻¹⁹ J and λ (nm) = 1240 / E (eV). A calculator is allowed.

Level: Physics grades 11-12 (A Level · IB · Class 11-12) · Curriculum: IB E.1

Time: 45 minutes · 8 questions · Total: 20 marks · Calculator allowed

Contents

Question 1 The electronvolt (2 marks)

Define the electronvolt. (1 mark)
Calculate 2.5 eV in joules. (1 mark)

Question 2 Reading a level diagram (3 marks)

The diagram shows some energy levels of an atom, and two transitions A and B.

Energy levels of the atom.

Calculate the energy of the photon emitted in transition A. (1 mark)
Calculate the wavelength of that photon. (1 mark)
Calculate the energy of the photon in transition B and state whether it is visible. (1 mark)

Question 3 Discrete emission (2 marks)

Explain why an atom of a gas emits light only at certain wavelengths.

Question 4 Dark lines in starlight (3 marks)

Explain how the dark lines in the spectrum of a star show which elements are present in its atmosphere.

Question 5 Hydrogen n = 5 to n = 2 (3 marks)

In hydrogen, level n = 5 is at −0.54 eV and level n = 2 is at −3.40 eV.

Calculate the energy of the photon emitted in the transition n = 5 → n = 2. (1 mark)
Calculate its wavelength. (1 mark)
State the region of the spectrum. (1 mark)

Question 6 Electron collision (2 marks)

An electron of kinetic energy 9.0 eV hits a hydrogen atom in the ground state. The smallest energy needed to excite the atom is 10.2 eV. Explain what happens.

Question 7 A 100 nm photon (3 marks)

A photon of wavelength 100 nm meets a hydrogen atom in the ground state (−13.6 eV). The next levels are at −3.40 eV, −1.51 eV and −0.85 eV.

Calculate the energy of the photon. (1 mark)
Deduce whether the atom can absorb the photon. (2 marks)

Question 8 Photons from a laser pointer (2 marks)

A laser pointer emits 5.0 mW of green light of wavelength 532 nm. Use h = 6.63 × 10⁻³⁴ J s and c = 3.00 × 10⁸ m/s.

Calculate the energy of one photon. (1 mark)
Calculate the number of photons emitted per second. (1 mark)

Define an energy level. — A discrete energy an electron in an atom may have.

Value of 1 eV in joules? — 1.60 × 10⁻¹⁹ J

Hydrogen ground-state energy? — −13.6 eV

Hydrogen level energy formula? — E = −13.6 eV / n²

Photon energy from a transition? — E = E initial − E final = hf

Wavelength from photon energy, nm and eV? — λ = 1240 / E

What is ionisation energy? — Energy to remove an electron from the ground state.

Appearance of an emission line spectrum? — Bright coloured lines on a dark background.

Appearance of an absorption spectrum? — A continuous spectrum crossed by dark lines.

Which hydrogen transition gives red light? — n = 3 to n = 2, at 656 nm