1/40 = 0.025 Hertz
It is 5 Hz.
f = 1/t = 1/0.025 = 40 Hz
That would also depends on the speed of the wave. The relationship is: speed = frequency x wavelength.
The speed c = 40 meters per second and the frequency f = 120 Hz. The wavelength lambda = c / f. Lambda = 40 / 120 = 0.3333333333 meters.
Divide the speed by the wavelength.
First of all there is no definition of retangular wave. Maybe your retangular is my square wave. and the answer is inconclusive unless you specify the 40% level.
10*4 = 40 metres per second
It seems you are talking about radio waves. The wavelength (40 m) multiplied by the frequency (7 million / second) must equal the speed of light (300 million meters/second). It seems that in this example numbers, either the wavelength or the frequency, or both, are not expressed with a great accuracy. For example, if 40 meters is exact, the frequency would be close to 7.5 MHz.
wavelength=velocity/frequency (v/f). wavelength=(3x10/4x10)=30/40=.75 meters
Frequency refers to how many waves pass a fixed point in a unit of time. Frequency is measured in Hertz, or Hz, and one Hertz means a single wave passes a given fixed point in one second. Wavelength refers to the length of an entire wave, so either from crest to crest or trough to trough. If you know how many waves pass a given point in a unit of time, which is frequency, and how long the waves are, which is wavelength, you can find the wave's speed. For example, if a wave has a frequency of 10 Hz, so ten waves pass a given point in a second, and it has a wavelength of four meters, you multiply the frequency by the wavelength to find that the waves are traveling at 40 meters per second.
Zirconium. Number 40 on the periodic table