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Intro to Forensic Science > Alternative Light Sources > Flashcards

Alternative Light Sources Flashcards

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1
Q

What is electromagnetic radiation?

A

Refers to various forms of energy in the form of waves which can be described by their wavelength.
Also known as light.
Between 380 and 750 nm which is visible to the human eye.

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2
Q

How is frequency used to measure light?

A

Frequency measures the number of waves that pass a given point in one second.

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3
Q
  1. How do X-rays take images?
A

a. X-rays are lower in energy, allowing them to pass through any matter (except bones and other dense material)

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4
Q

Waves are described by 3 factors:

A
  • Wavelength = distance between 2 consecutive peaks
  • Frequency = number of waves passing a single point within a particular time period
  • Speed = ~3.00 x 108 m/s
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5
Q

…..are discrete packets of energy that make up waves

A

Photons

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6
Q
  1. Is light described as a particle or a wave?
A

both Particle/Photons and wave.

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7
Q
  1. What numbers on the spectrum are visible to the naked human eye?
A

a. 400-700nm

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8
Q
  1. What wavelength comes before and after the wavelength visible to the human eye?
A

a. Infrared - before

b. UV - after

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9
Q
  1. How does light interact with objects?
A

When light strikes a surface it can be:

i. Reflected
- Bounces off surface
ii. Transmitted
- Passes through the surface
iii. Absorbed
- Taken in by the surface

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10
Q
  1. What are Gamma rays?
A

a. They are dangerous rays that can destroy cells.

b. They move very slowly and can pass through matter

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11
Q
  1. What is an orbital?
A

a. It is an energy level where an electron resides

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12
Q
  1. What wavelength does the highest frequency produce?
A

a. It produces the shortest wavelength

b. It produces Violet light on the spectrum

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13
Q
  1. What frequency does the longest wavelength produce?
A

a. Produces the lowest frequency and produces red.

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14
Q
  1. How does Infrared work and what is it used for?
A

a. Causes bonds between atoms to vibrate
- The amount of wavelengths absorbed by IR is different for every substance, making it suitable for use when identifying a pure substance

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15
Q
  1. What light is lower than the IR light?
A

The Microwave light

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16
Q
  1. What is the light at the lowest end of the light spectrum and can you describe it?
A
    • Radio waves are the lowest and produces low frequencies, long wavelengths and relatively little energy
      Carries radio and TV signals through a process called MODULATION.
17
Q
  1. What is Modulation?
A

a. When radio waves are transported through the air to the radio receiver by a carrier wave.
b. Can be accomplished through using amplitude (AM) or frequency (FM)

18
Q
  1. What happens when a substance is exposed to Electromagnetic radiation?
A

a. The light is absorbed and may or may not cause irreversible damage depending on the energy of the radiation.

19
Q
  1. What are the limitations of using UV light at a crime scene?
A

a. It does not distinguish or identify substances from one another.
i. I.e. Heroin and Morphine have very similar UV spectra

20
Q
  1. What is the process of “quantised”?
A

Process where the atom can only absorb the exact amount of energy

21
Q
  1. What is a popular solvent used for drugs?
A

Methyl alcohol

22
Q
  1. What is the most common UV/visible detector?
A

a. A photocell

b. Changes UV light into an electrical current

23
Q
  1. What is UV/visible microspectrophotometry?
A

The combination of UV light and a powerful microscope

24
Q
  1. What can spectroscopy be used for?
A

Identifying two different fibres
Identifying paint cip layers
Amount of substance in a mix

25
Q
  1. Does IR photons contain less energy than UV photons?
A

Yes

26
Q
  1. What is an important step to consider before conducting IR lighting tests?
A

a. Make sure the substance is purified

Because all substances absorb IR light

27
Q
  1. What can be analysed using IR microspectrophotometry?
A

a. Paint chips
b. Fibres
c. Drugs
d. Ink
e. Copier toners
f. Polymers
g. Dyes and pigments

28
Q
  1. How is IR used in Forensic science?
A

a. Used to analyse pure substances and identify them

b. If the sample is too contaminated, Mass spectroscopy and chromatography are preferred.

29
Q
  1. What is mass spectroscopy?
A
  • Measures & identifies substances.
    .Allows control of the energy source to reproduce the fragmentation pattern of a substance
    a. Mass spectrum of a pure substance is very reliable
    b. Can be designed for gas or liquid chromatography
30
Q

Cones in the eyes perceives what?

A 
Perceive colour
• 3 classes of cones:
• Short (Blue, absorbs at 420 nm)
• Medium (Green, 530 nm)
• Long (Red, 565 nm)
• Our eyes are most sensitive to green
31
Q

Name the three main retina layers in the eye:

A

1) Ganglion cell layer
2) Bipolar cell layer
3) Receptor cell layer (at the back of the eye).

32
Q

What are the two types of photoreceptor cells?

A

Rods- light

Cones - Colour.

33
Q

Name two Types of alternative light sources used

A

Ultraviolet (UV)- general to see
&
Infrared (IR)- for specifying

34
Q

Examinations used on paint- what is Polarised light microscopy used for?

A

Layer structure identification

35
Q

Examinations used on paint- what is Solvent and microchemical tests?

A

Very destructive- use to discriminate

36
Q

Examinations used on paint- what is IR Spectroscopy used for

A

Identifies binders, pigments and coatings.

Intro to Forensic Science (15 decks)

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