Drexel-SDP GK-12 ACTIVITY
Activity
Subject Area(s):
Nanotechnology, Size, Perspective, Comparison
Associated Unit:
Nanotechnology and Size Scaling
Associated Lesson
NanoScissors
Which is i
t:
Bigger or
Grade Level:
6-8
Time Required:
30-45 minutes
Group Size:
Entire Class [Groups of 3-4]
Expendable Cost per Group:
smaller?
minimal
Summary:
This is an exercise in distinguishing objects at differing length
scales. Students are given a group of images and guess what each object may
be. Students then form a hypothesis about the length of the bar on each image
compared to the other images (objects). They then rank them to see whether
their objects are large or small.
Engineering Connection:
This activity helps students realize the importance of
how microscopes are used to view objects which are much smaller than our eyes can
see. This information is typically used to tell scientists how things work internally and
help them understand how to improve performance of materials and devices.
Keywords: Microscopy, Size comparison, perspective, wavelength
Educational Standards
• Science: [PA] 3.1.7CDE, 3.2.7ABCD, 3.3.7AB, 3.4.7AB, 3.7.7AB
• Math:
[PA] 2.1.8ABD, 2.3.8AF, 2.4.8AB, 2.5.8B
Objectives
After this activity, students should be able to explain the basic difference between
how an optical microscope works compared to a scanning electron microscope. They
then should become familiar with the concepts of size scaling and perspective and be
able to deduce an approximate unit of length given limited knowledge of an otherwise
common object.
Materials List
Each group needs: SEM image handout, science notebooks
Introduction / Motivation
This activity typically requires little prep more than the handouts provided,
however for it to be as fun and effective a lesson as possible, it is important to show the
students the basic concepts of microscopy and the differences between optical
microscopy (which is most people's concept of a microscope) and the scanning electron
microscopes (SEM) that many scientist and engineers use throughout the world to
identify important problems that cannot be scene through optical methods.
Microscopy fundamental basis is its source's excitation wavelength. This is just a
fancy way of saying how a beam of energy is physically traveling. In order to see
objects in microscopes, the waves interact with the object. In the case of optical
microscopy, the wavelengths are in a range of light between 400-700nm. That means
that the smallest objects optical microscopes can resolve is a few hundred nanometers.
It also gives these microscopes less "depth" to see objects in 3D, which is discussed
later. Scanning electron microscopes use a high energy electron beam to see objects.
A very simple explanation of an electron as part of an atom is good enough, no need for
confusion. These wavelengths are much shorter than optical waves, approximately
2
0.02nm-1nm. This means these types of microscopes can see much smaller objects
than a normal microscope!
Vocabulary / Definitions
Word
Definition
Optical
Microscopes that use visible light as imaging source.
Microcope
Scanning
Microscopes that use electrons as imaging source.
electron
microscope
Resolution
The scale at which the smallest feature may be scene.
nanometer, 1 billionth of a meter, 1 millionth of a meter, 1 thousandth of a meter
micrometer,
millimeter
Procedure
1.
Briefly explain the concepts shown above to the students, at least so they may
understand that the images they are viewing are not taken by an ordinary camera, but
rather a sophisticated tool used by engineers to solve important technological problems.
2.
Next give the students the handouts provided. I found it is easier to give 3
students one set to all observe, but if paper is abundant everyone may get their own
set. Listed below is a master list for you to use during the activity. Make sure the
student number their images the same as is listed
below.
3.
3
The students first need to realize that a nanometer is one billionth of a meter. It
helps to either draw the decimal equivalent of this on the board as well as holding up
what a meter stick looks like in comparison. Another comparison is to tell the students
that finding one nanometer along the meter stick is equivalent of trying to find a single
golf ball in the state of Maryland. You can now choose whether or not to tell the
students information about the objects. Some find it fun to guess for a few minutes,
however this is an introduction to some difficult concepts and I found it necessary to at
least give the students some footing as to what each of these objects are. DO NOT
TELL THEM THE LENGTH SCALES YET! Just tell the its a bug eye, etc.
4.
Instruct the students to view each object carefully, comparing its features and
shapes to the other objects. Tell them it is important to realize that because an object
may appear large or small does not mean it is large or small, because it could be
magnified a great deal or not much at all. After viewing the images for a while ask them
to rank images 1-7 from largest to smallest.
5.
In addition, ask the students why image 8 is slightly blurry (you can tell them its
an optical image) while image 9 is not (an SEM image).
Assessment
The order of images should be: 4, 1, 2, 3, 7, 5, 6. This is chosen based on
smallest feature size in each image, for example, the bacteria in image 5 have a much
smaller width than their length.
The question posed in procedure 5 is explained by the way the electron
microscope receives its image. Unlike an optical microscope which takes a snapshot,
the electron microscope scans its wave across the sample many times at a very fast
rate. This scanning motion allows for a lot more detail to be seen as a result.
Owner
Drexel University GK-12 Program
Contributors: Adapted by Stephen Nonnenmann
Copyright
Copyright 2007 Drexel University GK12 Program. Reproduction permission is granted for nonprofit educational use
Version: Mar 2007
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