What is the theoretical limit of magnification for an optical microscope?
The resolution limit of an optical microscope is about 0.2 microns, which is equivalent to a magnification of 1500 to 2000 times; to achieve a larger magnification, an electron microscope or a tunnel scanning microscope must be used.
The magnifying glass can refocus the light to achieve the magnification effect, and the combination of the magnifying glass can obtain an optical microscope; the limit of the optical microscope is limited by the wavelength, and it is impossible to magnify infinitely.
In general, the resolution limit of an optical microscope at a fixed wavelength is half of the wavelength of light, and the wavelength of visible light is between 400 and 760 nm, so the resolution limit of an optical microscope is 200 nm (0.2 microns). Objects smaller than 0.2 microns cannot be resolved by an optical microscope, just as the tactile resolution of a human hand cannot exceed the small distance between tactile cells.
The magnification is a subjective statement. It is defined as the ratio of the size of the object seen by the human eye to the actual size when the photopic distance is 25cm. The resolution of an optical microscope of 0.2 microns is equivalent to a magnification of 1500~2000 times, which is enough for us to see Understand the structure of general cells.
Greater magnification can be achieved if we use electromagnetic waves with shorter wavelengths, but this is beyond the wavelength range of visible light; in 1931, British physicist Luska invented the electron microscope, based on the principle of wave-particle duality , the electron beam has a shorter de Broglie wave wavelength, so it can achieve a smaller resolution.
The accelerating voltage of electrons corresponds to its own wavelength. When the voltage is 100 kV, the wavelength of the electron beam is about 0.004nm (the actual resolution can only reach 0.2nm), which is also much smaller than the wavelength of visible light, so the resolution limit of the electron microscope is far The ultra-optical microscope can achieve a magnification of 3 million times and can distinguish tiny objects such as viruses, mitochondria, and DNA.
