Hot Colors eTrip: Sizing It Up Pre-Trip Lesson Plan
The student will:
- Appropriately use a microscope.
- Make estimates of the size of objects seen under a microscope.
- Use mathematics to convert common units of measurements into metric units.
- Microscopic samples (human hair, cheek cells)
- Thin clear plastic rulers marked with centimeters
- paper and pens/pencils
The markings on a microscope's objectives and eyepieces describe how many times bigger an object will appear. If the eyepiece is marked 10x, the eyepiece alone will make something appear ten times larger. When coupled with the objective, the magnification will be even greater. To calculate the microscope's magnifying power, multiply the power of the eyepiece by the power of the objective. For instance, if a 10x eyepiece is used with an objective marked 4x, the objects will appear forty (10 x 4) times larger.
It may be difficult to gauge a microscopic sample's actual size. Such samples are often measured in either millimeters or micrometers. A millimeter is 1/1000 of a meter, while a micrometer is 1/1000 of a millimeter. Although some microscopes come equipped with a special slide marked with a measuring scale in micrometers, it is also possible to make rough measurements using a ruler marked with metric measurements.
The following is a conversion of some units of measurement:
1 mile = 5280 feet
1 yard = 3 feet
1 yard = 0.91 meters
1 foot = 30.48 centimeters
1 inch = 2.54 centimeters
1 meter = 100 centimeters
1 meter = 1000 millimeters
1 centimeter = 10 millimeters
1 millimeter = 1000 micrometers
The instructor will:
- Write the conversion of measurements on the blackboard or prepare handouts with this information for the students.
- Provide the students with various measurements and ask them to convert them into different equivalents. For instance: convert 1 mile into yards (1,760 yards), 1 inch into millimeters (25.4 millimeters), 1 foot into meters (0.3048 meters), 1 centimeter into micrometers (10,000 micrometers), 1 inch into micrometers (254,000 micrometers), etc.
- Explain that microscopic objects are usually measured in micrometers or millimeters.
- Familiarize students with their microscopes. Likely the biggest challenge for students will be to find the right plane of focus. The instructor may want to suggest that students try to focus on objects that are somewhat familiar to them, such as the head of a pin.
- Instruct students to note the level of magnification on the microscope and record how many times larger objects will appear.
- Instruct students to place the plastic ruler on the stage of their microscopes.
- Direct students to examine the ruler under the low-power objective and move the ruler until it lies across the widest part (diameter) of their field of view.
- Instruct students to count the number of millimeter divisions they can see and record the number.
- Instruct students to convert the number of millimeters they have counted into micrometers. Record the conversion.
- Direct students to place a slide with a sample object (i.e. a grain of rice, human hair, cheek cells) under the microscope and move the sample so that it stretches across the center of the field of view under the microscope's low power.
- Instruct students to estimate how much of the field of view the sample fills.
- Direct students to compare this estimate with number of millimeters they measured in Step 8 and calculate a rough estimate of the object's size. For example, if the student first measured 10 millimeter marks across the field of view and now finds the grain of rice to cover approximately half of the field of view, the grain of rice is approximately 5 millimeters.
- Repeat Steps 8-10 with other objects.
Ability to calculate rough size estimates of microscopic samples
National Technology Standards
Levine, Shar and Leslie Johnstone. 1996. The Microscope Book. Sterling Publishing Co., Inc. 80 pages.