# Studying Cells - How Microscopes Work

• Studying Cells - How Microscopes Work
• Magnification is Size, Resolution is Detail
• Magnification is how much bigger the image is than the specimen (the sample you're looking at).
• It's calculated using this formula: magnification = image size / object size.
• Resolution is how detailed the image is.
• More specifically, it's how well a microscope distinguishes between two points that are close together.
• If a microscope lens can't separate two objects, then increasing the magnification won't help.
• You Need to be Able to Calculate the Magnification of an Image
• In the exam, you might be told the actual and magnified size of an object and then be asked to calculate the magnification. You can do this using the formula.
• You might also have to rearrange the formula to work out the image size or object size.
• You Need to Know About Three Types of Microscope
• Light microscopes
• Light microscopes use light.
• They have a lower resolution than electron microscopes - they have a maximum resolution of about 0.2 micrometres.
• So they're usually used to look at whole cells or tissues.
• The maximum useful magnification of a light x 1500 microscope is about
• Laser Scanning Confocal Microscopes (a special type of light microscope)
• Laser Scanning Confocal Microscopes use laser beams (intense beams of light) to scan a specimen which is usually tagged with fluorescent dye.
• The laser causes the dye to fluoresce - give off light.
• The light is then focused through a pinhole onto a detector.
• The detector is hooked up to a computer, which generates an image
• The image can be 3D.
• The pinhole means that any out-of-focus light is blocked, so these microscopes produce a much clearer image than a normal light microscope.
• They can be used to look at objects at different depths in thick specimens
• Electron Microscopes
• Electron microscopes use electrons instead of light to form an image. They have a higher resolution than light microscopes so give more detailed images. There are two kinds of electron microscope:
• Transmission electron microscope (TEM) - use electromagnet-s to focus a beam of electrons, which is then transmitted through the specimen
• Denser parts of the specimen absorb more electrons, which makes them look darker on the image you end up with.
• TEMs are good because they provide higher resolution images (so they can be used to look at a range of organelles) but they can only be used on thin specimens.
• Scanning electron microscopes (SEM) - scan a beam of electrons across the specimen.
• This knocks off electrons from the specimen, which are gathered in a cathode ray tube to form an image.
• The images produced show the surface of the specimen and can be 3D.
• But they give lower resolution images than TEMs.
• You Need to be able to compare Magnification and Resolution
• You need to know about the magnification and resolution of light microscopes and both types of electron microscopes.