DP Physics E.1 Structure of the atom

The diagram shows four energy levels for the atoms of a gas. The diagram is drawn to scale. The wavelengths of the photons emitted by the energy transitions between levels are shown. What are the wavelengths of spectral lines, emitted by the gas, in order of decreasing frequency?

• 3,2,1,4

• 4,1,2,3

• 4,3,2,1

• 4,2,1,3

Answer explanation

The diagram shows the position of the principal lines in the visible spectrum of atomic hydrogen and some of the corresponding energy levels of the hydrogen atom. Determine the energy of a photon of blue light (435 nm) emitted in the hydrogen spectrum. Answer: __x 10^-19 J

Answer explanation

Which statement about atomic spectra is not true?

• They provide evidence for discrete energy levels in atoms.

• Emission and absorption lines of equal frequency correspond to

  transitions between the same two energy levels.

• Absorption lines arise when electrons gain energy.

• Emission lines always correspond to the visible part of the

  electromagnetic spectrum.

Answer explanation

Emission lines can, in fact, correspond to ultraviolet and other non-visible parts of the

electromagnetic spectrum.

The element helium was first identified from the absorption spectrum of the Sun. Explain what is meant by the term absorption spectrum.

• An absorption spectrum is produced when photons are emitted by atoms transitioning to lower energy levels, resulting in bright lines against a dark background.

• An absorption spectrum is formed when light reflects off a solid surface, producing a continuous spectrum with no dark lines.

• When white light passes through a gas, photons can excite atomic electrons into higher energy levels. When this happens, the photon is absorbed, resulting in a dark line in the spectrum.

• An absorption spectrum is created when photons are absorbed by the nucleus of an atom, causing nuclear decay and resulting in dark bands.

It is found that alpha particles with a kinetic energy of 7.7 MeV bounce back off an aluminum target. If the charge of an aluminum nucleus is 12.1 x 10^-18 C, calculate the velocity of the alpha particles (they have a mass of 6.7 x 10^-27 kg). Answer: __x 10⁷ m/s