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Microscope and Microscopy - Transmission Electron Microscope (TEM)-advanced

Grade 9CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The Transmission Electron Microscope (TEM) is an advanced microscopy technique where a beam of electrons is transmitted through an ultra-thin specimen, interacting with it as it passes through.

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The resolution of a microscope is limited by the wavelength of the radiation used. Since the wavelength of electrons (calculated via de Broglie's equation) is significantly shorter than visible light, TEM can achieve resolutions down to 0.10.1 to 0.2 nm0.2 \text{ nm}, compared to 200 nm200 \text{ nm} for light microscopes.

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Instead of glass lenses, TEM uses electromagnetic lenses to focus the electron beam. These lenses consist of coils of wire that generate a magnetic field to manipulate the path of the charged electrons.

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The interior of a TEM must be maintained under a high vacuum (P≈10−4P \approx 10^{-4} to 10−8 Pa10^{-8} \text{ Pa}) to prevent electron scattering by air molecules.

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Specimen preparation is critical: samples must be extremely thin (usually <100 nm< 100 \text{ nm}) so that electrons can pass through them without being completely absorbed.

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The resulting image is a 2D 'shadowgraph' that provides detailed information about the internal structure of organelles, viruses, and even large molecules.

📐Formulae

M=Size of ImageSize of ObjectM = \frac{\text{Size of Image}}{\text{Size of Object}}

d=0.61λnsin⁡θd = \frac{0.61 \lambda}{n \sin \theta}

λ≈1.22V nm\lambda \approx \frac{1.22}{\sqrt{V}} \text{ nm}

💡Examples

Problem 1:

A researcher observes a ribosome using a TEM. If the actual size of the ribosome is 25 nm25 \text{ nm} and the image produced on the screen measures 2.5 cm2.5 \text{ cm}, calculate the magnification used.

Solution:

First, convert all units to the same scale. Let's convert 2.5 cm2.5 \text{ cm} to nanometers (1 cm=107 nm1 \text{ cm} = 10^7 \text{ nm}): Image Size=2.5×107 nm=25,000,000 nm\text{Image Size} = 2.5 \times 10^7 \text{ nm} = 25,000,000 \text{ nm} Using the magnification formula: M=25,000,000 nm25 nmM = \frac{25,000,000 \text{ nm}}{25 \text{ nm}} M=1,000,000×M = 1,000,000 \times

Explanation:

Magnification is a dimensionless ratio. By converting the image size from centimeters to nanometers, we find that the TEM has enlarged the object one million times.

Problem 2:

Compare the theoretical resolution (dd) of a light microscope using light of wavelength λ=500 nm\lambda = 500 \text{ nm} and a TEM using an electron beam with an effective wavelength of λ=0.005 nm\lambda = 0.005 \text{ nm}, assuming the numerical aperture (NANA) is 1.01.0 for both.

Solution:

Using the resolution formula d=0.61λNAd = \frac{0.61 \lambda}{NA}: For Light Microscope: dL=0.61×500 nm1.0=305 nmd_L = \frac{0.61 \times 500 \text{ nm}}{1.0} = 305 \text{ nm} For TEM: dT=0.61×0.005 nm1.0=0.00305 nmd_T = \frac{0.61 \times 0.005 \text{ nm}}{1.0} = 0.00305 \text{ nm} Ratio of resolution: dLdT=3050.00305=100,000\frac{d_L}{d_T} = \frac{305}{0.00305} = 100,000

Explanation:

Because the wavelength of the electron beam is 100,000 times smaller than visible light, the TEM can resolve features that are 100,000 times smaller than those visible under a light microscope.