2.1- Microscope Flashcards
What is magnification?
Magnification describes how much bigger an images appears compared with the original object. Microscopes produce linear magnification which means that if a specimen is seen magnified *100 , it appears to be 100 times longer than it really is.
What is resolution?
Resolution is the ability of an optical instrument to see or produce an image that shows fine details clearly
What does high resolution mean?
The image will be more detailed, clearer and sharper.
What is the difference between magnification and resolution?
Magnification is the number of times larger an image appears, compared with the size of the object, whereas resolution is the clarity of an image.
Why are optical microscopes important?
The development of optical (light) microscopes played a key role in our understanding of cell structure. They were the first sort to be used.
Why are optical microscopes used in schools, colleges, hospitals and research labs?
As they are:
- relatively cheap
- Easy to use
- Portable and able to be used in the field as well in laboratories
- Able to be used to study whole living specimens.
What do present day light/optical microscopes and 17th century light/ optical microscope require?
Both microscopes may look different but both types rely on lenses to focus a beam of light.
What is the highest magnification of an optical microscope?
Optical microscopes allow magnification up to *1500, or in some types *2000, which enables us to see clearly some of the large structures inside cells.
Why cant optical microscopes magnify higher than 1500/200?
Because their resolution is limited and cannot magnify any higher while still giving a clear image.
What type of source does an optical microscope use to magnify a specimen?
Optical microscope use visible light, a part of the electromagnetic spectrum that has a wavelength between 400-700nm
Why will the structures close together appear as one object in an optical microscope?
The wavelength of visible light ranges from 400-700nm so structures closer together than 200nm (0.2um) will appear as one object.
Why do ribosomes not appear when using a light microscope?
Ribosomes are very small, (non-membrane), cell organelles of about 20nm diameter and so they cannot be examined using a light microscope.
How do you use an optical microscope?
1) The specimen on a slide is placed here on the stage and clipped into place
2) By rotating the nose-piece, the lowest power objective lens is placed over the specimen
3) Adjust the coarse focus knob, while looking into the eyepiece, until the image you see is clear and in focus.
4) Whilst viewing the image adjust the iris diaphragm for optimum light.
5) Make sure the object you wish to view is directly over the hole in the stage. Now rotate the nose piece and bring the*10 object into the place of the specimen. Look down the ocular tube and use the fine focus knob to focus the image.
How do you carry an optical microscope?
When you carry an optical microscope you should hold it by its arm in one of your hands, whilst having another under the base of the microscope.
How do you calculate total magnification?
total magnification= objective* eyepiece
What is the image being viewed by an optical microscope called?
Photomicrograph
What are laser microscope also called?
Confocal microscope
What type of source does a laser microscope?
They use laser light to scan an object point by point and assemble, by computer the pixel information into one image displayed on a computer screen
What type of resolution does a laser microscope have?
High resolution and shows high contrast
Why can a laser microscope be used to clearly observe whole living specimens?
These microscopes have depth selectively and can focus on structure at different depths within a specimen, therefore they can be used to clearly observe whole living specimens
How are laser microscopes used effectively in the medical profession?
They are used in the medical profession, for example to observe fungal filaments within the cornea of the eye of a patient with a fungal cornea infection, in order to give a swift diagnosis and earlier- making it more effective
Why does an electron microscope have a greater resolution than an optical microscope?
Electron microscopes use a beam of fast travelling electrons with a wavelength of about 0,004nm. This means that they have much greater resolution than optical microscopes and cane be used to give clear and highly magnified images.
How are electrons fired in the microscope?
The electrons are fired from cathode and focused, by magnets rather than Glass lenses on to a screen or photographic plate.
Why does an electron microscope have a BETTER resolution than an optical microscope?
Fast travelling electrons have a wavelength about 125 000 times smaller than that of the central part of visible light spectrum. This accounts for an electron microscope much better resolution compared with an optical microscope.
How is the specimen prepared for a transmission electron microscope?
The specimen has to be chemically fixed by being dehydrated and stained
What do the beam of the electrons in a transmission electron microscope do?
The beams of electrons passes through the specimen, which is stained with metal salts. Some electrons pass and are focussed on the screen or photographic plate.
What do the electrons form in a transmission electron microscope?
The electrons form a 2D black and white image.
What is the image produced by a transmission electron microscope called?
An electron micrograph
When was a scanning electron microscope developed?
During the 1960’s
How is a 3D image produced in a scanning electron microscope?
Electrons don’t pass through the specimen, which is whole, but cause secondary electrons ‘bounce off’ the specimen surface and be focussed on to a screen. This gives a 3D image with a magnification from *15 up to *200,000. The image is black and white, but computer software programmes can add false colour. However the specimen still has to be placed in a vacuum and is often coated with a fine film of metal.
What are 2 types are electron microscope?
Transmission
Scanning
What are the problems with using both types of electron microscope?
- Are large and very expensive
- Needs a great deal of skill and training to use
Why do specimens have to be dead when using electron microscopes?
Specimens, even whole ones for use in SEMS,have to be dead as they are viewed while in a vacuum.
What are the metallic salt stains used for?
The metallic salt stains used for staining specimens may be potentially hazardous to the user.
