We present here very detailed ac measurements of the convection heat flux

{\vec{J}}_{2}^{h}

and the induction electric field

\vec{E}

associated with the moving vortex lines in a low-

κ

type-II superconductor (Pb-4.56-at.% In). The measurements were made using an original low-frequency current-modulation method based on a second-sound technique.

{\vec{J}}_{2}^{h}

and

\vec{E}

have been measured as functions of the applied magnetic field

H_{e}

and the applied electric current density and frequency

ν

(

300 < ν < 1200

Hz) in the temperature range between 1.3 and 2.1 °K. The great accuracy of this ac method allows us to observe some interesting details in the

{\vec{J}}_{2}^{h} (H_{e})

and

\vec{E} (H_{e})

curves. In particular,

{\vec{J}}_{2}^{h} (H_{e})

reverses its direction at low fields (

H_{e} ≳ H_{c 1}

), while

\vec{E} (H_{e})

remains in the same direction in the whole of the mixed state. This reversal effect suggests that, due to the presence of nonlocal effects in our low-

κ

alloy (

κ \approx 1.25

), there are vortex lines of opposite sign in the superconductor. Furthermore, we have observed that

{\vec{J}}_{2}^{h} (H_{e})

vanishes only for fields larger than the upper critical field

H_{c 2} (T)

. The transported entropy

S_{D}

per unit lenght of flux line per flux quantum computed from these measurements was found to be independent of the applied current density and frequency. In the high-field region (

H_{e} ≲ H_{c 2}

) experimental values of

S_{D}

are in good agreement with the theoretical predictions of Caroli and Maki in the dirty limit. The calorimetric entropy per vortex line was obtained theoretically from the free-energy forms in the mixed state and compared with

S_{D}

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