Continuous and Line Spectra Flashcards
What is a black body?
A body that emits all possible wavelengths for the temperature of that body.
It is capable of absorbing all the radiation that falls on it.
Since it does not reflect energy from any other source, all the energy radiated is thermal energy due to its temperature.
This radiation froms continuous spectrum
What is an experiment that involves black bodies?
If two thermometers, one of which has the bulb painted black, are placed near a heat source, the reading of the thermometer with the black bulb rises more quickly showing that it is absorbing more energy
What are the different ‘states’ to an atom?
The lowest energy level is called the ground state.
If an electron gains energy it can move to a higher energy level. It is now in an excited state.
If the electron gains enough energy to completely remove it from the atom it is said to be in an ionization state.
What happens after an electron has been excited?
If an electron is in an excited state it can return to a lower energy level. When it does this, it will lose energy.
The amount of energy it loses will be equal to the difference in the energy levels it moves between. This energy is released as a photon.
As the energy levels have different values, each of the possible electron transitions within an atom will produce a photon with a different energy.
This means that each electron transition will produce a photon of a different frequency and hence a different colour.
This causes line emission spectra to be produced
Define continuous spectrum
Spectrum that contains no gaps; all frequencies are present.
Define electron volt
One electron volt is the energy gained by an electron when it is accelerated by a potential difference of 1 V. The energy gained is the potential different multiplied by the charge
What is the absorption spectrum of a star?
Some frequencies absorbed by (cooler) gases/material
Frequencies missing from the spectrum as dark lines appear in the spectrum
Light remitted in all directions (so less intense towards Earth)
Characteristic of the elements present in the star/enables red shift to be observed
Describe how the light from a star could be collected and analysed in order to find its wavelength.
Light collected by telescope
Diffracted by grating
Angle of diffraction measured
Diffraction grating equation
Explain what is meant by the term emission line spectrum.
Atoms are excited Photons emitted Discrete wavelengths/photon energies Characteristic of element Electrons change energy levels Observed with a spectrometer
State the difference between the appearance of a continuous emission spectrum and that of a line emission spectrum.
Continuous range of frequencies not discrete frequency
State one laboratory source of a continuous spectrum
Incadescent, white hot body
The spectrum of the Sun consists of a continuous spectrum crossed by dark lines. State the name for this type of spectrum and explain how the dark lines arise.
Absorption
Absence of light at dark line
