We talk a lot about the importance of "passion" in the classroom, but does it really help students learn? Well, in fact, it can. At the very least, a passionate instructor who demonstrates his or her emotions in the classroom is a very motivating speaker. Emotions add emphasis to the content of a lecture and underline the importance of certain topics. In addition, the passion is infectious -- if you can get excited about a particular topic, then perhaps it is not so dull after all!
But over and above the presentational benefits of passion, there is a definite link to learning. Harry Murray of UWO's Psychology Department has shown that instructors who are very expressive, use a lot of nonverbal behaviour, and move around the classroom are very effective. Not only do they receive higher ratings, but students actually perform better on exams. This effect may result from several factors. For example, the passionate instructor is more likely to maintain student attention and, consequently, there is a greater focus on the material to be learned. In addition, being in a positive mood, in general, tends to have this focusing effect -- as long as the mood is moderately positive. Being in an extremely good mood can be just as distracting as being in a negative mood.
One potential problem is a mood-congruity effect. We tend to remember better if we are in the same mood at recall as we were at learning. So if students are in a positive mood during a lecture, they will recall the information better if they are also in a positive mood during the exam. Nonetheless, the benefits of "passion" are well documented and can provide a boost to student learning.