1.What is a comparison microscope? What are the advantages of this microscope?
2.What are the three substances that generally make up paint? Describe each part. 3.What are polymers?
4.What is a scanning electron microscope? What are its advantages? 5.What is the PDQ? What is it used for?
Critical Thinking Questions
1.What are some of the challenges for forensic scientists in dealing with fiber evidence? 2.What does it mean if a paint sample "matches" a known sample from a vehicle? Does this indicate the same source? Why or why not? 3.Why are microscopes important to forensic scientists?
4.How does trace evidence end up transferring to the crime scene, suspect, or victim? Discuss some of the ways that this might happen. What elements of paint can help forensic scientists compare samples to each other? Another microscope that is commonly used is a comparison microscope. A comparison microscope combines two microscopes into one module, allowing the viewer to see what is under each of the lenses at the same time. This is particularly helpful for examining a piece of evidence with a known sample, since the two samples can be examined side by side. When using a comparison microscope, forensic scientists have to be sure to set the two objective lenses to the same magnification and other settings.
A stereoscopic microscope provides a three-dimensional image of the item, although it does not have the magnifying power of a compound microscope. Because of the ease of using this microscope and its good depth of field, the stereoscopic microscope may be the most commonly used microscope in the forensic laboratory. It can more easily handle larger items and can often present a clearer, wider image of evidence.
A scanning electron microscope works by shooting a beam of electrons at the item and recording the electron emissions that occur. The recorded electron emissions are then shown on a computer screen as the image. This makes the scanning electron microscope (SEM) different from other microscopes that use lenses to magnify the image. One advantage of an SEM is that it can achieve high rates of magnification (up to 10,000 times) and it tends to have a better depth of field while magnifying than compound microscopes. Forensic scientists may use an SEM to determine whether a suspect's hands had gunpowder residue on them, for example, by examining the tape that has been used to lift particles off of the suspect's hands.