Electromagnetic wave:
It is an oscillating particle wave derived and emitted in space by electric and magnetic fields in the same phase and perpendicular to each other. It is an electromagnetic field that propagates in the form of waves and has wave-particle duality. Electromagnetic waves move in the form of waves through electric and magnetic fields that oscillate in the same phase and are perpendicular to each other, and their propagation direction is perpendicular to the electric field. Electromagnetic waves have a fixed speed in a vacuum, and this speed is the speed of light. See Maxwell equations.
The electric field direction, magnetic field direction and propagation direction of electromagnetic waves are perpendicular to each other, so electromagnetic waves are shear waves. When its energy level jumps over the critical point of radiation, it radiates outward in the form of light. At this stage, the wave body is a photon, and sunlight is the visible radiation form of electromagnetic waves. Electromagnetic wave does not depend on the medium, and the propagation speed in vacuum is equal to the speed of light. Electromagnetic radiation ranges from low frequency to high frequency, and is mainly divided into radio waves, microwaves, infrared rays, visible light, ultraviolet rays, X rays and gamma rays. The electromagnetic wave that human eyes can receive is called visible light (wavelength 380~780nm). The amount of electromagnetic radiation is related to temperature. Generally, all substances or particles above absolute zero have electromagnetic radiation. The higher the temperature, the greater the radiation, but most of it is invisible to the naked eye.
Ultrasonic wave:
It is a sound wave with a frequency higher than 20000 Hz. It has good directivity, strong penetration ability, easy to obtain concentrated acoustic energy and long propagation distance in water. It can be used for ranging, measuring speed, cleaning, welding, crushing, disinfection and so on. It has many applications in medicine, military, industry and agriculture. Ultrasound is named because its lower frequency limit is greater than the upper hearing limit of human beings.
Scientists call the number of vibrations per second the frequency of sound, in hertz. The frequency of sound waves that our ears can hear is 20Hz-20000Hz. So we call the sound wave with frequency higher than 20000 Hz "ultrasonic wave". The ultrasonic frequency usually used for medical diagnosis is 1 MHz -30 MHz.
The essential difference between them is that the propagation of electromagnetic waves does not need medium, while ultrasonic waves need medium. Electromagnetic waves such as light waves and ultrasonic waves are all sound waves, and vacuum cannot spread.
Du's success is certainly not accidental, but inevitable on the road of wisdom. Juan Zhe studied Mr. Du for several years and