1. 1
   A beam of alpha particles, all with the same kinetic energy, is directed at a gold foil about 400 atoms thick inside an evacuated chamber. A small zinc sulfide screen that flashes when struck by an alpha particle can be moved to any angle around the foil. Almost all the alpha particles pass through the foil undeflected or are deflected by less than a few degrees. About 1 in 8000 is deflected through more than 90°, and a very few rebound almost straight back towards the source.

   (a)

   Which conclusion is supported by the observation that almost all the alpha particles pass through the foil with little or no deflection?

   [1 mark]

   • AThe positive charge of the atom is spread evenly throughout its volume
   • BThe nucleus carries a negative charge
   • CMost of the volume of an atom is empty space
   • DElectrons have a mass similar to that of alpha particles

   (b)

   Why is the experiment carried out in an evacuated chamber?

   [1 mark]

   • ATo stop the gold foil from oxidising during the experiment
   • BTo make the alpha particles travel faster than they would in air
   • CTo remove background radiation from the chamber
   • DTo prevent the alpha particles being absorbed or slowed by collisions with air molecules

   (c)

   Explain why only a very small fraction of the alpha particles rebound through more than 90°.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Naturally occurring iron contains atoms of the nuclide $^{56}_{26}\mathrm{Fe}$ and a smaller proportion of $^{58}_{26}\mathrm{Fe}$. Nickel also has a common nuclide, $^{58}_{28}\mathrm{Ni}$.

   (a)

   How many neutrons are in a nucleus of $^{56}_{26}\mathrm{Fe}$?

   [1 mark]

   • A26
   • B30
   • C56
   • D82

   (b)

   Which statement about $^{58}_{26}\mathrm{Fe}$ and $^{58}_{28}\mathrm{Ni}$ is correct?

   [1 mark]

   • AThey have the same number of nucleons
   • BThey are isotopes of the same element
   • CThey have the same number of neutrons
   • DThey have the same number of electrons when neutral

   (c)

   Compare the composition of a neutral atom of $^{58}_{28}\mathrm{Ni}$ with that of a neutral atom of $^{58}_{26}\mathrm{Fe}$.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A particular gas has atomic energy levels at −10.4 eV (the ground state), −5.5 eV, −3.7 eV and −1.6 eV. When a high voltage is applied across a tube of the gas, a student looking through a spectroscope sees two bright visible lines, at wavelengths of 590 nm and 689 nm, on a dark background.

   (a)

   Determine the photon energy, in eV, of the 590 nm line and identify the transition that produces it.

   [3 marks]

   (b)

   The discharge is switched off and white light is passed through the same gas at room temperature. Deduce whether dark lines would be seen at 590 nm and 689 nm, and at which wavelengths absorption would be expected instead.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Light from a distant star passes through a spectroscope. The spectrum is a continuous band of colours crossed by dark lines at 393 nm, 397 nm, 486 nm, 589.0 nm, 589.6 nm and 656 nm. In the laboratory, heated gases give the following bright emission lines: hydrogen at 410 nm, 434 nm, 486 nm and 656 nm; sodium at 589.0 nm and 589.6 nm; helium at 588 nm and 668 nm; calcium ions at 393 nm and 397 nm.

   (a)

   Explain how emission and absorption spectra provide evidence that the electrons in atoms occupy discrete energy levels, and explain how the dark lines in the star's spectrum are formed.

   [6 marks]

   (b)

   Evaluate the extent to which the data show which elements are present in the star's outer layers.

   [6 marks]

   Total for question 4: 12 marks

End of questions