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Scientists can analyse light from stars that has passed through a diffraction grating - Edexcel - A-Level Physics - Question 17 - 2023 - Paper 2
Question 17
Scientists can analyse light from stars that has passed through a diffraction grating. (a) Explain the pattern produced when a mixture of blue and red light, from t... show full transcript
Worked Solution & Example Answer:Scientists can analyse light from stars that has passed through a diffraction grating - Edexcel - A-Level Physics - Question 17 - 2023 - Paper 2
Step 1
(a) Explain the pattern produced when a mixture of blue and red light, from the same source, passes through a diffraction grating.
Answer
When light passes through a diffraction grating, it interferes as it emerges from the slits. In this case, when a mixture of blue and red light is involved, two distinct diffraction patterns can be observed. Blue light has a shorter wavelength compared to red light, resulting in a greater angle of diffraction for blue light according to the formula:
where:
- is the grating spacing,
- is the angle of diffraction,
- is the order of the maximum,
- is the wavelength of the light.
As blue light diffracts more, it appears further from the centerline of the pattern than red light, which creates a colorful pattern with blue light appearing on the outer sides and red light closer to the center.
Step 2
(i) Explain how this leads to the formation of the dark lines within the spectrum.
Answer
As light from the star passes through its atmosphere, it interacts with the elements present there. Atoms in the atmosphere absorb specific wavelengths of light corresponding to energy levels of electrons. When an electron absorbs energy, it can move to a higher energy level, leaving gaps in the spectrum where this light is not emitted, creating dark lines, known as absorption lines. The presence of these dark lines helps us identify the elements in the star's atmosphere and provides valuable information about its composition.
Step 3
(ii) On the axes below, sketch a graph of the intensity of radiation against the wavelength of that radiation for this star.
Answer
To sketch the graph, plot intensity on the vertical axis and wavelength on the horizontal axis. The curve should represent a continuous distribution of intensity, peaking at the wavelength corresponding to the star’s surface temperature, following Planck's law for black body radiation. At 5800 K, the peak will be in the visible range, indicating higher intensity at certain wavelengths and showing dips at wavelengths absorbed by elements in the star's atmosphere.
The curve should rise to a maximum and then taper off towards longer and shorter wavelengths.
Step 4
(iii) Explain why main sequence stars do not collapse due to gravitational forces.
Answer
Main sequence stars are in a state of hydrostatic equilibrium, which means the gravitational force pulling inward is balanced by the outward pressure from nuclear fusion occurring in the core. In the core, hydrogen fuses into helium, releasing energy in the form of radiation and heat. This energy creates an outward pressure that counteracts the force of gravity. As long as the fusion process continues, this balance is maintained, preventing the star from collapsing.