There are oodles of web-based Audience Response apps available that students can use their mobile devices to respond to ("oodles" is in fact a scientific quantity). In this post we'll take a look at Poll Everywhere (yes, it's free!).
Poll Everywhere allows you to create polls or surveys, then provide your students with an access link. The polls can also be embedded within Powerpoint or Google Slides, a nice touch to any presentation. Here's a short survey example so you can get an idea of the different types of questions available:
Trouble accessing this poll? Try accessing it at pollev.com/denisec573, then think of the possibilities!