Digging up the Past Flashcards
Current
the rate of flow of charge
Potential Difference
amount of energy needed to pass through a component per coulomb
Resistance
energy used per amp of flow
Large current
low resistance
How does the resistance change with size?
wider - lower resistance because there’s more area for charge carriers to pass through
Potential Divider circuit
- two different resistors in a circuit
- the terminal potential difference of a supply is divided between series resistors in the ratio of their resistance
Balancing the potential
you can find the EMF by finding the balancing point where the potentials are equal
‘Common’ current flow
positive to negative (electrons travel the other way)
Electromagnetic spectrum
Radio waves, Microwaves, Infra Red, Visible Light, Ultra Violet, X-rays, Gamma Rays
Radio waves end of EM spectrum
low frequency, low energy, long wavelength
Gamma rays end of EM spectrum
high frequency, high energy, short wavelength
Why do we see light of a particular wavelength?
because the sun gives out light and we’ve evolved to see light of this wavelength it gives out
How are x-rays used in archaeology?
they can be used to find out the content of artefacts, to look at things such as a mummy without destroying or damaging it, they can be used to assess the condition of archaeological finds
Diffraction
the spreading out of a wave as it passes through a gap
How do you get maximum diffraction?
if the size of the gap is similar to the wavelength
How can diffraction patterns be used?
to identify the structure of atoms and other molecules/objects
Why do TEM and SEM work?
because electrons can act like waves
Electron microscopes (transmission or scanning)
beam of electrons scan across to build up an image
TEM
transmission electron microscope
SEM
scanning electron microscope
How does a TEM work?
- ‘light’ source at top of microscope emits electrons
- they travel through a vacuum in the column of the microscope
- electromagnetic lenses focus the electrons into a thin beam which travels through the specimen
- some electrons scatter and ‘disappear’ while the rest hit a fluorescent screen which creates a shadow image (varied darkness due to varied density)
Why use electrons in a microscope?
their lower wavelength makes it possible to get a resolution a thousand times better than a light microscope
How does a SEM work?
- electrons fired into a vacuum, are accelerated but the electron beam bounces off specimen and the image is formed of the reflected electrons shown on a screen
- the electron beam is repeatedly swept across the specimen to build the image in detail
Dating Techniques
- Carbon dating
- Dendrochronology
- Half life dating
Half life dating
- you can work out how much of something radioactive is given off using a Geiger counter
- then if you know the half life of it you can work out how many half lives it’s gone through to reach the amount you’ve measured and count back how old it is
Dendrochronology
- trees grow by adding rings
- analysing and comparing growth ring patterns of trees and aged wood allows you to know the date cut down so you can count back the age
Good conductors
low resistivity
Good insulators
high resistivity
Semiconductors
in the middle of the resistivity spectrum
Metals have
free electrons
Where are potential divider circuits used?
In sensors for street lamps or ovens that stop heating once they reach a certain temperature
Diffraction grating
a regular array of very narrow lines ruled on transparent plastic/glass this is placed in front of the laser and produces a diffraction pattern
Diffraction
the spreading out of a wave as it passes through a gap
Interference
when coherent waves undergo superposition and reinforce or cancel each other out
Superposition
when two waves interfere and pass through each other either summing or cancelling amplitudes
How does an electron gun work
- electrons are ‘boiled’ off a heated filament by thermionic emission
- they are attracted towards a positive anode accelerated by a potential difference
- some electrons pass through the vacuum and hit the graphite target
- others pass through the graphite sheet and diffract before hitting the the graphite target
