What single property of the illumination sets a microscope's resolution limit?
The wavelength — smaller wavelength gives better (smaller) resolvable distance.
State the Abbe resolution relationship.
d=λ/(2NA); resolution d is proportional to wavelength.
Best resolution of a light microscope and why?
~200 nm, because visible light wavelength (~500 nm) limits it via d=λ/2NA.
Best resolution of a TEM?
~0.2 nm (electron wavelength ~0.004 nm is far shorter than light).
TEM vs SEM — beam path?
TEM: electrons pass through a thin specimen (internal 2D). SEM: electrons scan across the surface (3D image).
Why can't EM view living specimens?
The column is a vacuum (electrons scatter in air), which kills cells.
Define magnification.
Image size divided by actual size: M=image/actual.
What is an artefact?
A false structure produced by specimen preparation, not present in the living cell.
Why are raw electron micrographs black and white?
Electrons have no visible colour; colour is added by computer afterwards.
A 60 mm image at ×3000 — actual size?
60/3000=0.02 mm =20μm.
Recall Feynman: explain to a 12-year-old
Imagine feeling for a tiny pebble with a big beach ball — the ball is too clumsy to feel the gap between two pebbles, so they feel like one lump. Light is like that big ball: it can't squeeze into super-tiny gaps. Electrons are like feeling with a needle tip — super thin, so they can tell two tiny things apart. That's why electron microscopes see way more detail. The catch: electrons hate air and need everything dead and dried first, and they can't see colour — so we paint the pictures in later.
Dekho, microscope ka asli kaam sirf bada dikhana (magnification) nahi hai — asli cheez hai resolution, yaani do paas-paas wale points ko alag-alag dikhana. Aur resolution depend karta hai wavelength par. Visible light ki wavelength ~500 nm hai, isliye light microscope 200 nm se chhoti cheez resolve nahi kar sakta, chahe magnification kitni bhi badha do. Formula simple: d=λ/2NA — jitni chhoti wavelength, utni achhi (chhoti) resolution.
Electrons ki wavelength bahut hi chhoti hoti hai (~0.004 nm at 100 kV), light se lagbhag 1,00,000 guna chhoti. Isliye TEM ~0.2 nm tak resolve kar leta hai — ribosome, membranes, sab dikh jaata hai. Yahi ek fact se EM ki saari power aati hai.
TEM vs SEM yaad rakhne ka trick: T = Through (electrons specimen ke aar-paar nikalte hain, andar ka 2D structure dikhta hai), S = Surface (electrons surface par scan karte hain, 3D shape dikhti hai). TEM ki resolution best hai, SEM thodi kam par 3D image deta hai.
Lekin EM ke nuksaan bhi hain: vacuum chahiye isliye living cell nahi dekh sakte, preparation se artefacts ban sakte hain, machine mehngi aur badi hoti hai, aur image black-and-white hoti hai (colour baad mein computer se daalte hain). Light microscope chhota, sasta, colour deta hai aur living cells dikha sakta hai — isliye dono ki apni jagah hai. Exam mein bas yaad rakho: magnification badhane se detail nahi badhti, resolution badhane se badhti hai!
