convert landscape and portrait files

I have some dozen jpg files together, some landscape oriented, some
portrait.
How do I convert the jpgs, so that the width only is always (eg) 500 px ?

When I convert it as below, the longest between width/height gets
resized to 500 px.

blau:~$ for i in *.jpg; do convert "$i" -resize 500 \
"${i//.jpg}"-500.jpg; done

Blau