  A 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 is based on a field-tested approach in which students
realize their difficulties after predicting the outcome of simulated
experiments involving a lock-in amplifier and check their predictions using the
simulated lock-in amplifier. Then, the tutorial provides guidance and strives
to help students develop a coherent understanding of the basics of a lock-in
amplifier. The tutorial development involved interviews with physics faculty
members and graduate students and iteration of many versions of the tutorial
with professors and graduate students. The student difficulties with lock-in
amplifiers and the development and assessment of the research-based tutorial to
help students develop a functional understanding of this device are discussed.
