Q.Briefly explain the principle and working of electron microscope.

Step 1. Principle: the resolving power of a microscope -- its ability to distinguish two closely spaced points -- is inversely proportional to the wavelength of the radiation used to illuminate the object; a shorter wavelength buys higher resolving power and magnification.

Step 2. An electron's de Broglie wavelength, at typical accelerating voltages, is many thousands of times shorter than the wavelength of visible light used in an optical microscope, so an electron beam can, in principle, resolve far finer detail.

Step 3. Working: an electron microscope's construction mirrors an optical microscope's exactly, with the electron source replacing the light source, and magnetic or electrostatic lenses replacing every glass lens -- the electron beam, passing through a suitably arranged electric or magnetic field, converges or diverges just as light does through a glass lens.

Step 4. Electrons from the source are accelerated by a high potential and made roughly parallel by a magnetic condenser lens; as the beam passes through the specimen it picks up the specimen's image information, and a magnetic objective lens followed by a magnetic projector lens system forms the final magnified image on a photographic plate. …

State the resolving-power-vs-wavelength principle first, then trace the electron beam's path through the microscope's magnetic l …

• Omitting the underlying principle (shorter wavelength gives higher resolving power) …