Physics - The universe Flashcards
What is a diffraction grating?
A piece of material with lines on it that produce a spectrum which diffuses light.
What is a continuous emission spectrum?
A complete spectrum of colours showing all wavelengths of light.
eg. star or a filament bulb usually from matter that is very hot it emits light.
What is a line emission spectrum?
A series of bright lines on a dark background. Produced by hot gases. Hot gasses do not emit all wavelengths of light.
What is a line absorption spectrum?
A series of dark lines on a continuous emission spectrum. Produced by a cool gas with a hot continuous source behind it - such as a star.
What are Fraunhofer lines?
Joseph von Fraunhofer invented a device called a spectroscope which contained a diffraction grating. When he used this device to analyse the light coming from the Sun he discovered dark lines on a continuous spectrum. These are called
Fraunhofer lines.
How are absorption lines produced and what do they show?
-The Sun and other stars produce all wavelengths of light. As this light passes through the cooler outer atmosphere, gas atoms absorb certain wavelengths of the light, producing a line absorption spectrum which we see from Earth.
-Scientists were able to compare these dark lines with the line emission spectra of the known elements and identify what elements were in the cooler atmosphere.
What is the doppler shift?
-When an object that emits waves begins to move, the movement can cause the stretching or compressing of the waves.
-For example, when an ambulance is travelling towards an observer, he will hear a higher pitch – a higher frequency note. The sound wavelength is compressed by the movement of the ambulance towards the observer.
How does the doppler shift effect stars?
- Light wavelengths from an object emitting light are stretched by movement away from the observer. This is called the red shift. This means stars going away from us appear red.
- Light wavelengths from an object emitting light are compressed by movement towards the observer. This is called the blue shift. This means stars coming towards us appear blue.
What did Edward Hubble discover?
-Hubble noticed that the absorption spectrum lines from galaxies showed the same pattern as the Sun’s absorption spectrum – showing that the same elements were present, but the lines had been shifted towards the red side of the visible spectrum.
-He concluded that the stretched waves meant that the galaxies were moving away from us.
What is the cosmological red shift?
The shift of line absorption spectra from galaxies to the red part of the visible spectrum. Caused by the light passing through expanding space, which stretches the wavelengths.
What is Hubble’s law?
This shows that the velocity of a galaxy is directly proportional to its distance away from Earth. In other words, if the distance of the galaxy away from us doubles, so does its recessional velocity.
What is Hubble’s constant?
The Hubble constant (H) is the gradient of the graph.
It gives us the age of the Universe – currently thought to be around 13.7 billion years.
What is Lemaître’s big bang theory?
The scientific theory that describes the early development of the Universe. It says that the whole Universe expanded out from a small, hot, dense region. Hubble’s research evidences this as the red shift of galaxy light showed that the Universe was expanding, and that the galaxies had originated from a single point.
What is cosmic microwave background radiation (CMBR)?
Radiation that started life as gamma waves but was stretched into longer wavelength microwaves by the Universe expanding.
How does CMBR evidence the big bang theory?
The short wavelengths of the gamma radiation emitted in the initial explosion are believed to have become stretched due to the expansion of space into longer wavelength microwaves.
