GUESS TUTORIAL
Playlist: Wave Basics
Name:
In order to solve GUESS problems, you must be familiar with all the symbols and units used for each variable. The
symbol is the letter that will appear in the equation itself. The unit appears next to the numbers in the problem itself.
This information is on your equation reference sheet.
Variable
Wave speed
Wavelength
Frequency
Symbol
v
λ
f
Unit
m/s
m
hz
Sample Problem:
Explanation of steps:
A wave with a frequency of
30 hz moves with a speed of
240 m/s. What is the
wavelength?
First, you can tell that this is a GUESS problem because there are numbers in the
question.
Givens:
f = 30 hz
v = 240 m/s
Givens: During this step you are pulling the givens (the numbers out of the problem). It is
really important that you know what piece of information each number is giving you.
You figure this out, by looking at the units behind the number in the problem. For
example, the first number is 30 hz. To figure out what hz measures I can go up to the
table above (or to your equation sheet) and look for hz. Hz turns out to be units of
frequency so now I know that 30 hz is the frequency of the wave. Once you’ve done this,
it is important to write down the symbol of each given. So I get f = 30 hz.
Unknown:
λ=?
Unknown: Identify what the question is asking you to find. Usually, this in the first
sentence or the last sentence. In this case, it’s asking us to find wavelength. Again I must
also figure out what the symbol is from my equation sheet. For wavelength, the symbol
is λ.
Equation:
v=fλ
Equation: This is the most important step. Now you have to go to your equation sheet.
Look at all the equations and find an equation that has your givens AND your unknown.
So our givens are v and f. And our unknown is λ. So we go through the equations one by
one until we find one that has all three.
Substitute:
(240 m/s) = (30 hz) λ
Substitute: Here, you plug in your given numbers into the equation. Our givens give us v
and f. So we will plug in 240 for v and 30 for f.
Solve:
(240 m/s) = (30 hz) λ
Solve: In this last step, you have to do the algebra to solve for the unknown variable. In
this case the unknown, λ, is not by itself so we have to do some algebra to figure out the
answer. The 30 hz is multiplying so we have to do the inverse operation, division to solve
for the unknown. So we divide both sides by 30 hz.
8 meters = λ
Never forget to include units in your answer!! Your answer has no meaning and cannot
be considered correct if it does not have units.