  We investigate the Interface Region Imaging Spectrograph (IRIS) observations
of the quiet-Sun (QS) to understand the propagation of acoustic waves in
transition region (TR) from photosphere. We selected a few IRIS spectral lines,
which include the photospheric (Mn~{\sc i} 2801.25~{\AA}), chromospheric
(Mg~{\sc ii} k 2796.35~{\AA}) and TR (C~{\sc ii} 1334.53~{\AA}), to investigate
the acoustic wave propagation.The wavelet cross-spectrum reveals significant
coherence (about 70\% locations) between photosphere and chromosphere. Few
minutes oscillations (i.e., period range from 1.6 to 4.0 minutes) successfully
propagate into chromosphere from photosphere, which is confirmed by dominance
of positive phase lags. However, in higher period regime (i.e., greater than
$\approx$ 4.5 minutes), the downward propagation dominates is evident by
negative phase lags. The broad spectrum of waves (i.e., 2.5-6.0 minutes)
propagates freely upwards from chromosphere to TR. We find that only about 45\%
locations (out of 70\%) show correlation between chromosphere and TR. Our
results indicate that roots of 3 minutes oscillations observed within
chromosphere/TR are located in photosphere. Observations also demonstrate that
5 minute oscillations propagate downward from chromosphere. \textbf{However,
some locations within QS also show successful propagation of 5 minute
oscillations as revealed by positive phase lags, which might be the result of
magnetic field}. In addition, our results clearly show that a significant
power, within period ranging from 2.5 to 6.0 minutes, of solar chromosphere is
freely transmitted into TR triggering atmospheric oscillations. Theoretical
implications of our observational results are discussed.
