  The lock-in amplifier is a versatile instrument frequently used in physics
research. However, many students struggle with the basic operating principles
of a lock-in amplifier which can lead to a variety of difficulties. To improve
students' understanding, we have been developing and evaluating a
research-based tutorial which makes use of a computer simulation of a lock-in
amplifier. The tutorial allows students to realize their conceptual
difficulties by comparing their predictions about how a lock-in amplifier will
behave with the outcome of simulated experiments. After being confronted with
discrepancies between their predictions and the lock-in amplifier results, the
tutorial targets the common difficulties that students have and leads them to
develop a deeper understanding of the principles of lock-in amplification.
