2.1.1 microscopes

Question 1

magnification

Answer 1

how much bigger an object appears compared to the original

Question 2

what magnification do microscopes produce

Answer 2

linear magnification

Question 3

resolution

Answer 3

ability of an optical instrument to see/produce an image that shows fine detail clearly

Question 4

why are optical microscopes good for schools etc. to use

Answer 4

• relatively cheap
• easy to use
• portable —> used in field/labatories
• study whole living specimens

Question 5

what magnification do optical microscopes allow

Answer 5

up to x1500 (some types = x2000)

Question 6

what type of light do optical microscopes use and what does this mean

Answer 6

• use visible light
• wavelength of visible light 400-700nm so structures closer than 200nm appear as 1 object

Question 7

describe how to set up a microscope

Answer 7

1. place slide with specimen on onto stage & clip
2. by rotating the nosepiece, select the lowest power objective lens
3. adjust coarse focus knob (whilst looking in eyepiece) until image is clear/focused
4. adjust iris diaphragm for optimum light
5. rotate nosepiece & bring 10x objective lens over specimen - look down ocular tube & use fine focus knob to focus image
6. repeat step 5. using x40 objective lens

Question 8

calculation for magnification

Answer 8

total magnification = magnifying power of objective lens x magnifying power of eyepiece lens

Question 9

photograph of image taken using an optical microscope

Answer 9

photomicrograph

Question 10

what are laser scanning microscopes also called

Answer 10

confocal microscope

Question 11

characteristics of laser scanning microscopes

Answer 11

• use laser light & assemble onto computer
• high resolution & high contrast
• depth selectivity
• observe whole living specimens & cells
• used in medical profession
• used in branches of biological research

Question 12

describe electron microscopes

Answer 12

• use beam of fast travelling electrons (wavelength ~0.004nm)
• greater resolution
• give clear & highly magnified images

Question 13

where are the electrons fired from in an electron microscope & how is a image created

Answer 13

• fired from cathode
• focused by magnets onto a screen or photographic plate

Question 14

describe transmission electron microscopes

Answer 14

• specimin chemically fixed —> dehydrated & stained
• beam of electrons pass through specimen (stained with metal salts)
• form 2D black-and-white image
• produce magnification up to 2 million times

Question 15

what is the image formed by a transmission electron microscope called

Answer 15

electron micrograph

Question 16

describe scanning electron miscroscopes

Answer 16

• electrons don’t pass through whole specimen but cause secondary electrons to bounce off
• image focused onto screen
• 3D image
• magnification from x15 to x200,000
• black-and-white image but false colour can be added
• specimen placed in vacuum & coated in fine metal film