Light as a wave Flashcards
What is n in relation to monochromatic light
the order of the beam
What is d in relation to monochromatic light
distance between gratings on diffraction grating. Must be in metres
What is angle for formulae in relation to monochromatic light
Theta is the angle from the zeroth order to the point you are looking at on the screen
How can you find the measure of the angle for the experiment of monochromatic light
use tan of angle = opposite over adjacent
In the experiment to estimate the wavelength of monochromatic light what would happen to the position of the images if wavelength of light was decreased
They would get closer
In the experiment to estimate the wavelength of monochromatic light what would happen to the position of the images if there were less lines on the refraction grating
They would get closer
What is a spectrometer
An optical instrument used to examine spectra and to measure the wavelength of light
Explain the parts of the spectrometer
Turntable,
The vernier Scale
Slit- needs to be as narrow as possible so accurate image is found
Collimator- Convex lens at one end and narrower tube has slit
Telescope- Free to rotate. Has cross wires t enable exact image position to be determined
Give the steps in using the spectrometer
- move eyepiece until cross threads are in focus
- Focus on distant object moving cross theads and eyepiece to focus
- Illuminate slit and look through telescope
- Move slit relative to collimator so it’s in focus
- Adjust width of slit
- Level table
Explain diffraction
Spreading of a wavefront into the geometrical shadow when it passes through a gap or around an obstacle
What type of wave is light
electromagnetic wave
How do you make diffraction more noticeable
If gap or obstacle is approximately equal to or less than the wavelength of the wave
What is the grating constant of a diffraction grating
The distance between two adjacent slits on the grating
Explain monochromatic light and give two sources
Not a of different wavelengths (ie. Cannot be broken into a number of colours) ex: Laser, Sodium vapour lamp
Describe what happens to monochromatic light that falls on a diffraction grating
Light passes through slits in diffraction grating and diffraction occurs.
The diffracted waves overlap and interference occurs
Destructive interference occurs- no light visible
Constructive interference occurs- light visible
Light that passes straight through grating is the zero order image
What is the formula for diffraction grating
n(lamda) = dsin(Angle)
What is the formula for the maximum order image
n(lamda) = dsin(90)
Explain polarisation
The process of confining the vibrations of the light wave to one direction
What happens if light passes through a substance called polaroid
It becomes plane polarised.
Polaroid absorbs the light vibrating at right angles to it’s axis and only allows light that is vibrating parallel to it’s axis pass through.
Explain stress polarisation
Two pieces of polaroid held at right angles so no light passes through- polarised
Light can pass through if perspex is placed in between as direction of light vibration changes
When viewed from right hand side different colours of light are observed.
Colour pattern changes if perspex is under strain
Explain dispersion and name two methods
The separating out of wavelengths (colours) present in light is called dispersion
Describe light that is dispersed by a prisim
Red light bends the least and violet bends the most. It results in one spectrum
Describe light that is dispersed by grating
Red light bends mos, violet bends least and spectrum is formed for each value of n other than n=0. No dispersion for zero order image
How does a rainbow occur
Dispersion is responsive. For rainbow to occur sunlight and moisture in air is needed (h20)
What is recombination
A second prisim will recombine the constituents of white light to again form white light
What are the primary colours of light
Three colours that combine to give white light- red, green, blue
What are the secondary colours of light
Obtained by combining any two primary colours
Yellow = red and green
Cyan= blue and green
Magenta- red and blue
What are complementary colours of light
A primary and secondary colour that combine to give white light are complementary colours
Blue + yellow
Red + Cyan
Green + Magenta
Describe the speed and type of waves that electromagnetic waves are
In a vacuum they travel at 3x10^8
They are all transverse waves and can be polarised
Name the types of electromagnetic radiation on the electromagnetic spectrum from smallest wavelength to biggest
Gamma ray X-ray UV Visible Light Infrared Microwaves TV and radio waves
What is the approx wavelength of gamma ray
0.01nm
What is the approx wavelength of X-ray
1nm
What is the approx wavelength of UV
0.1μm
What is the approx wavelength of Visible light
0.4μm-0.7μm
What is the approx wavelength of Infrared
0.01mm
What is the approx wavelength of Microwaves
1cm
What is the approx wavelength of Tv and Radio waves
1km
Explain line spectrum in terms of light production
source of light is luminous gases and vapours at low pressure ex: sodium vapour
Explain band spectrum in terms of light production
sources is molecules of glowig gases or vapours ex: oxygen or nitrogen gas
Explain continuous spectra in terms of light production
Could consist of all the colours in white light. The source is an incandescent solid or liquid eg: tungsten filament lamp
Explain incandescent
White hot
What can produce UV light in life and in lab
A white hot solid can produce UV light - Sun
In the lab ordinary filament lamp emits a small amount or usually a mercury vapour lamp is used
How it UV light detected
Effect on a photographic plate or by Fluorescence- absorbs UV light and emits it as visible light
What are the properties of UV light
Causes certain substances to fluoresce- vaseline
Effects photographic plate more than visible light
Causes sunburn
Produces vitamin D in skin
Does not pass through ordinary glass only quartz glass
High frequency so it emits electrons from metal surfaces (photoelectric effect)
What emits IR radiation?
All hot objects emits IR radiation ex: human body or exhaust pipe of car. As temperature increases objects emits more IR radiation of shorter wavelength
How is IR radiation detected
Using thermometer with blackened bulb
What are the properties of IR radiation
Effects photographic plate- can take photo in dark
Thermogram
Passes through fog and mist- photographs
Causes substances on which it falls to heat up
Explain Greenhouse effect
Some radiation penetrates atmosphere and is absorbed by earth then re emitted
Wavelength of re-emitted is longer and cannot pass through atmosphere so it keep planet warm
Gas CO2 traps this radiation
Since CO2 levels are rising with burning of fossil fuels temperature of earth is rising.
