# wave amplitude, frequency,wavelength,energy

1. While understanding mechanical wave, if i just sit in front of the pond and throw a stone, there is a ripple formed. I want to understand the ripple in terms of the sine wave depicted in text books. Is the sine wave form in text books depicts the movement of a point (The point where the stone hits the water) in the wave(up and down or horizontal movement of water?). What is the wavelength of the ripple? Is it same as saying when one point goes up down in the ripple how long it takes for the next particle to start the up-down movement? I know wave form depicts the energy transfer. I want to know the physical meaning of the amplitude and frequency. Is it the water particle vibration?

2. In electromagnetic wave there is no physical movement of matter. In this case how should i understand the frequency and wavelength. Is it vibration of the source electron only. Since EM travels at light speed, we need not worry about what is the shape?

• In case 1) there isn't any movement of matter, only its oscillation. What dissipates is the energy. In case 2) there is the movement of photons, emitted from accelerated electrons. Depending from the acceleration value the photon has different energy content-for visible light (say from an fire) - from red (lower energy photons) to blue. Since in double slit experiments photons of different energy content produce different distances between fringes this was related to wavelengths and frequencies. – HolgerFiedler Oct 2 '16 at 8:59
• Mechanical simple harmonic waves - physicskey.com/34/waves-and-mechanical-simple-harmonic-waves – Saral Dec 29 '18 at 6:52

What is the wavelength of the ripple?

If you look at the pond, you can see the wavelength with your eyes: It is the distance between two crests of the wave.

Is it same as saying when one point goes up down in the ripple how long it takes for the next particle to start the up-down movement?

Yes, you need the propagation speed of the wave in order to convert the wavelength to a period $T$ for one oscillation. This period is the inverse of the frequency: $T = 1/f$.

Is the sine wave form in text books depicts the movement of a point (The point where the stone hits the water) in the wave (up and down or horizontal movement of water?)

The sine wave in the book depicts the surface shape of the water. From your question I'd say it is the horizontal movement, but there is a slight catch. In a water wave, the water actually only moves up-down! You can easily check this by putting something on the water (leaves, pollen, sawdust) and create some waves. You will see that the waves travels through the stuff on the surface, the swimming thing will move mostly up and down and does not travel with the wave.

I want to know the physical meaning of the amplitude and frequency.

The amplitude is the height that the water gets lifted above the normal height when the wave passes by.

The frequency is the number of up-down movements of a particular point within one time period.

Is it the water particle vibration?

I wouldn't call it vibration as it happens on a larger scale. But otherwise I think you can say that.

In electromagnetic wave there is no physical movement of matter. In this case how should i understand the frequency and wavelength.

There is movement of matter if that matter is charged. Actually you need some charged matter (electrons) in order to detect the field in the first place; you need an antenna.

The EM wave will take the electrons in the antenna and move them along. The stronger the wave, the higher the voltage you can pick up from the antenna.

The frequency here is again the number of times that the electrons get shaken up-down in a period of time. The wavelength is the distance between to crests of the wave. You can measure this by taking two antennas and spacing them apart. If the electrons in both antennas get pulled up at the same time, the antennas are a wavelength (or a multiple of that) apart. If one antenna has a positive voltage while the other one has a negative one, and vice versa, they are half a wavelength (or $n + 1/2$ wavelengths) apart.