IT IS THE MOST ADVANCED FORM OF MICROSCOPE.IN em ,object and lens are placed in a vacuum chamber and a beam of electrons is passed though object.electrons pass through or are reflected from object and make image . electromagnetic lenses enlarge and focus the image onto a screen or photographic film.electron microscope  has much higher resolving power than light microscope. the most modern em can distinguish objects as small as 0.2 nanometer (nm) and 1 nm =1/1000,000 mm. it is a thousand _fold improvement over ln .em can magnify object about 250,000 times. under special conditions em can detect individual atoms. cell organelles and even molecules like DNA and protein are much larger than single  atoms