The answer is wave B has a lower frequency. Suppose these waves represent the sound of a siren on a passing ambulance. Wave B (lower frequency) represents the sound of the siren after it has passed you. The ambulance moving towards the observer produces a higher than normal frequency, and the ambulance moving away produces a lower than normal frequency.
Gasoline comes from petroleum, which is a fossil fuel. Petroleum, coal and natural gas (methane) are all made in the earth's crust from the bodies of plants and animals that died long ago. That's why they are called fossil fuels.
The sun provides the energy that all life needs to grow and reproduce. Therefore, fossil fuels can be considered a form of solar energy that has been stored in the bodies of living things, and then concentrated in hydrocarbon deposits in the earth's crust.
The fact is that all the energy on earth comes from the sun, directly or indirectly, except for nuclear energy, which comes from radioactive elements that were made in other stars that existed before the sun.
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The hot gases produce their own characteristic pattern of spectral lines, which remain fixed as the temperature increases moderately.
<h3><u>Explanation: </u></h3>
A continuous light spectrum emitted by excited atoms of a hot gas with dark spaces in between due to scattered light of specific wavelengths is termed as an atomic spectrum. A hot gas has excited electrons and produces an emission spectrum; the scattered light forming dark bands are called spectral lines.
Fraunhofer closely observed sunlight by expanding the spectrum and a huge number of dark spectral lines were seen. "Robert Bunsen and Gustav Kirchhoff" discovered that when certain chemicals were burnt using a Bunsen burner, atomic spectra with spectral lines were seen. Atomic spectral pattern is thus a unique characteristic of any gas and can be used to independently identify presence of elements.
The spectrum change does not depend greatly on increasing temperatures and hence no significant change is observed in the emitted spectrum with moderate increase in temperature.
