  We show how the nature of the the phase transition in the two-dimensional
bimodal Ising spin glass model can be understood in terms of elementary
excitations. Although the energy gap with the ground state is expected to be 4J
in the ferromagnetic phase, a gap 2J is in fact found if the finite lattice is
wound around a cylinder of odd circumference $L$. This 2J gap is really a
finite size effect that should not occur in the thermodynamic limit of the
ferromagnet. The spatial influence of the frustration must be limited and not
wrap around the system if $L$ is large enough. In essence, the absence of 2J
excitations defines the ferromagnetic phase without recourse to calculating
magnetisation or investigating the system response to domain wall defects. This
study directly investigates the response to temperature. We also estimate the
defect concentration where the phase transition to the spin glass glass state
occurs. The value $p_c = 0.1045(11)$ is in reasonable agreement with the
literature.
