  We present optical and ultraviolet (UV) photometry and spectra of the very
nearby and highly reddened supernova (SN) 2014J in M82 obtained with the Swift
Ultra-Violet/Optical Telescope (UVOT). Comparison of the UVOT grism spectra of
SN~2014J with Hubble Space Telescope observations of SN2011fe or UVOT grism
spectra of SN~2012fr are consistent with an extinction law with a low value of
R_V~1.4. The high reddening causes the detected photon distribution in the
broadband UV filters to have a much longer effective wavelength than for an
unreddened SN. The light curve evolution is consistent with this shift and does
not show a flattening due to photons being scattered back into the line of
sight. The light curve shapes and color evolution are inconsistent with a
contribution scattered into the line of sight by circumstellar dust. We
conclude that most or all of the high reddening must come from interstellar
dust. We show that even for a single dust composition, there is not a unique
reddening law caused by circumstellar scattering. Rather, when considering
scattering from a time-variable source, we confirm earlier studies that the
reddening law is a function of the dust geometry, column density, and epoch. We
also show how an assumed geometry of dust as a foreground sheet in mixed
stellar/dust systems will lead to a higher inferred R_V. Rather than assuming
the dust around SNe is peculiar, SNe may be useful probes of the interstellar
reddening laws in other galaxies.
