Grade 10 Bio Microscope Quiz

How a Microscope Works

Bending Light: The objective (bottom) convex lens magnifies and focuses (bends) the image inside the body tube and the ocular convex (top) lens of a microscope magnifies it (again).

The Parts of a Light Microscope

Light source

Could be a mirror, but most likely it is a bulb built into the base

Diaphragm

Adjusts the amount of light striking an object

Ocular lens

Gathers light and magnifies image. Usually 10X.

Objective lens

Magnifies objects (4X, 10X, 40X) and focuses light to your eye.

Stage

Holds slide. Can be moved using the coarse or fine adjustment knobs to bring the object into focus.

Stage clips

Hold slide in place

Base and arm

Structural support for the microscope

Resolution

the ability to distinguish between two objects that are very close together

Electron versus light microscopes

Light microscopes are limited by their resolution.

• Light microscopes cannot produce clear images of objects smaller than 0.2 micrometers (1 mm = 1000 μm)

Electron microscopes use beams of electrons, rather than light, to produce images

• Electron microscopes can view objects as small as the diameter of an atom

Types of Electron Microscopes

Specimens from electron microscopy must be preserved and dehydrated, so living cells cannot be viewed

• Transmission electron microscopes (TEMs) pass a beam of electron through a thin specimen

• Scanning electron microscopes (SEMs) scan a beam of electrons over the surface of a specimen

Caring for a Microscope

Clean only with a soft cloth/tissue

Make sure it’s on a flat surface

Don’t bang it

Carry it with 2 HANDS…one on the arm and the other on the base

Using a Microscope

Start on the lowest magnification

Don’t use the coarse adjustment knob on high magnification…you’ll break the slide!!!

Place slide on stage and lock clips

Adjust light source

Use fine adjustment to focus

Magnification

To determine your magnification…you just multiply the ocular lens by the objective lens

Ocular 10x Objective 40x: 10 x 40 = 400

So the object is 400 times “larger”

Total Magnification

Total Magnification : ocular (10x) times the objective lens

Low power : 10x * 4x = 40x

Medium power : 10x * 10x = 100x

High power : 10x * 40x = 400x

Field Diameter

distance across the field of view

      note: 1 mm = 1000 μm

• Low power [40x] = 4.5 mm   = 4 500 μm

• Medium power [100x] = 1.8 mm   = 1 800 μm

• High power [400x] = 0.45 mm =    450 μm

Finding Field Diameter

If you find field diameter on a low power magnification, you can use this to calculate the field diameter at higher magnifications

Field of View

whole circular area that you see when you look through the microscope

Calculating Estimated Actual Size of a Specimen

Field diameter

• Determine by evaluating which objective lens was used to view specimen

• Ensure units are μm

# of specimens fitting across field diameter

• Estimate how many specimens fit across the field diameter width wise