R. Lutfi, CD202

Here's a game we play in this class. I call it the game of three questions. It starts with a problem on an exam something like this:

The stakes are high. If you can do the problem you get to declare a major in communicative disorders, if not, the unthinkable - you must take the final. Not everyone is up to the challenge, many stumble and end up psychology majors. Don't let this happen to you. Master the game of three questions:

QUESTION (1): What is the problem asking for?

Start easy - simply identify what the problem asks for. This at least tells you what the final answer should look like.

Answer: The problem asks for a value in dB re: 0.04 dynes/cm². The notation 're:' means 'relative to' or 'in reference to'.

QUESTION (2): How is this different from what is given?

Knowing how the final answer differs from what is given tells you more about the final answer and helps you decide what to do next.

Answer: The problem asks for a quantity in relation to a larger reference than what is given: 0.04 dynes/cm² versus 0.0002 dynes/cm². This means that in relative terms the final answer must be smaller than what is given - smaller than 13 dB.

QUESTION (3): By how much?

The final step is to identify the factor and convert to dB . By what factor does a quantity change when the reference increases from 0.0002 dynes/cm² to 0.04 dynes/cm²?

Answer: By a factor of 0.0002/0.04, and because this is a change in pressure the corresponding change in dB is 20log(0.0002/0.04) = -46.

Practice the game of three questions and angels will light your path beyond the gates of Goodnight Hall.