Microscopes

Question 1

Magnification definition

Answer 1

• magnification: how many times larger the image is compared to the object I=AM
• resolution: minimum distance between 2 objects in which they can still be viewed as separate

Question 2

Optical (light) microscope

Answer 2

• a beam of light is condensed to create the image
  Negatives
• lower resolution than electron microscope due to light having a longer wavelength, small organelles not visible, lower magnification, creates 2D images
  Positives
• colour images, can view living samples , cheap and portable, specimen is easy to prepare

Question 3

Electron microscopes

Answer 3

• a beam of electrons is condensed to create the image, electromagnets are used to condense the beam
• the vacuum environment is needed so that particles in the air do not deflect the electrons out of the beam alignment
• higher resolving power as electrons have a short wavelength
• higher magnification

Question 4

Transmission electron microscope

Answer 4

• use electromagnetism to focus a beam of electrons which is transmitted through specimen
• areas that absorb the electrons appear darker on the electron micrograph
  Negatives
• whole system must be in a vacuum so no living specimen can be viewed, complex staining process, specimen must be extremely thin, may contain artefacts, creates 2D images
  Positives
• can see sub-cellular structure, high magnification and resolution

Question 5

Scanning electron microscope

Answer 5

• a beam of electrons passes across the surface and bounce of the surface, which builds up a 3D image depending on the contours of the specimen
  Negatives
• whole system must be in a vacuum so living specimens cannot be viewed, image may contain artefacts (less of a problem as it has a lower resolution than TEM)
  Positives
• creates 3D images, can see the surface texture of specimens in detail, specimen do not need to be thin, high magnification and resolution

Question 6

Converting units

Answer 6

Metre —> millimetre x1000
Millimetre —> micrometre x1000
Micrometre —> nano metre x1000

Question 7

Eye piece graticule

Answer 7

• inside of optical microscopes there is a scale on a glass disc which is called the eyepiece graticule
• this can be used to measure the size of objects you are viewing under the microscope
• eac time you change the objective lens, and therefore the magnification, you have to calibrate the eyepiece to work out the distance between each division represents at that magnification