Question

Which equation will give you the speed of a wave?
A. speed = frequency + wavelength
B.speed = amplitude/2
C. speed = frequency x wavelength
D.speed = wavelength + frequency

Answer 1

C.

Answer 2

option C

Answer 3

Even if you knew nothing about waves, you can use dimensional analysis combined with the common meanings of the words to eliminate the wrong answers. Dimensional analysis simply means that the equation must make sense in terms of the units of additive terms. For example, you won't want to add time and distance.

Frequency refers to how often something happens, like 3 times per second. The units of frequency are therefore 1/second.

Wavelength, you can suspect, has units of length, or meters. It doesn't make sense to add meters to 1/seconds. (also A & D are the same so they can't both be right so they must both be wrong).

Similarly, amplitude and speed are not the same concept so it cant be B; you don't add or subtract speed and amplitude.