  The eigenstates of a single massless Dirac particle confined in a linear
potential are calculated exactly by direct solution of the Dirac equation. The
electromagnetic structure functions are calculated from the Dirac wave
functions of the ground and excited states of the particle by coupling to its
conserved vector current. We obtain the longitudinal and transverse structure
functions as a function of y=nu-q, where nu and q are the energy and momentum
transferred to the target in its rest frame. At values of q>~2.5 GeV, much
larger than the characteristic energy scale ~440 MeV of the confining
potential, the response exhibits y scaling, a generalization of Bjorken
scaling. We compare the exact structure functions with those obtained from the
ground state wave functions in the plane wave impulse approximation. The
deviation from the Callan-Gross relation is compared with the parton model
prediction.
