Pre-Lab 7: Atomic Spectra Section Name Date Reading ✓ Solved

06 Pre-Lab 7: Atomic Spectra Name Section Date Reading

The following hypothesis is a classical theory which tries to explain why a light bulb emits light. It is classical because it ignores the wave-like properties of atoms.

Hypothesis 1: Incandescent light comes from a tungsten filament encased in a glass bulb.

1. Electric current passes through the tungsten filament and heats it up.

2. Tungsten atoms vibrate randomly when heated. They move more when they are hotter.

Questions

Question 1:

Use the fact that atoms are made of charged protons and electrons to explain why the random vibration produces light.

Question 2:

Consider an experiment where you produce waves on a string by moving one end up and down with your hand. What is the relationship between the frequency of your hand (i.e., the number of times per second you move your hand up and down) and the frequency of the wave on the string?

Question 3:

What do you think is the relationship between the frequency of atomic vibration in the tungsten filament and the frequency of emitted light? Based on this hypothesis, what frequencies should be present in the light emitted by the filament?

Question 4:

If the atoms are hotter, then we can expect that they will move faster and farther. What do you think that this would do to the brightness of the light? What about the color of the light?

Question 5:

What is the energy transformation which occurs when light is produced? In other words, where does the energy for the light come from? Give answers in terms of both macroscopic and microscopic energies.

Paper For Above Instructions

The phenomenon of incandescent light emission from a tungsten filament in light bulbs is rooted in classical atomic theory. According to this theory, light produced by a tungsten filament involves an interplay between electric current, atomic structure, and energy transformation.

Question 1 Analysis

Atoms, consisting of charged protons and electrons, exhibit random vibrational motion when heat is applied, such as when an electric current passes through the tungsten filament. When these atoms gain energy from the current, their electrons jump to higher energy levels, also known as excited states. As these excited electrons return to their original or ground states, they release energy in the form of photons—particles of light. This process occurs due to the electromagnetic interaction between the charged particles within the atom. The energy emitted corresponds to specific wavelengths of light, rendering the visible spectrum observable to the human eye (Heisenberg, 1927).

Question 2 Analysis

The relationship between the frequency of hand movement and the resulting wave frequency on a string is directly proportional. When a person moves their hand up and down at a certain frequency, they create waves in the string that oscillate at the same frequency. This principle underscores the wave nature of energy transfer, as seen with waves along the string where the wave frequency mirrors that of the applied motion (Kirchhoff, 1882).

Question 3 Analysis

Returning to the tungsten filament’s atomic vibrations, we can infer a similar relationship with emitted light frequency. As the filament's temperature increases due to electric current, the frequency of atomic vibration rises, which enhances the energy of the emitted photons. Therefore, higher temperatures yield light of greater frequencies, which aligns with the principles of black-body radiation. Consequently, we can expect emission of light frequencies that span across the visible spectrum, including red, yellow, and blue light, depending on the filament's temperature (Planck, 1901).

Question 4 Analysis

With an increase in atomic temperature, the speed and amplitude of atomic vibrations increase, leading to heightened brightness in light output. Brighter light stems from a greater number of emitted photons with higher energy. The color of the light also shifts, wherein increased temperatures will often change light outputs toward the blue end of the spectrum. This phenomenon is interpreted through Wien's displacement law, which states that the peak wavelength of emitted radiation shifts to shorter wavelengths as the temperature rises (Wien, 1893).

Question 5 Analysis

The energy transformation involved in light production inherently derives from electrical energy supplied to the tungsten filament. As the electric current encounters resistance within the filament, it converts electrical energy into thermal energy, heightening atomic movements and ultimately resulting in the emission of light. This transformation can be expressed in macroscopic terms as electrical energy converting to thermal energy, which then prompts light emission. On a microscopic level, these processes revolve around electron transitions between different energy levels, leading to photon emission (Einstein, 1905).

Conclusion

The understanding of incandescent light generation through the behavior of tungsten atoms under electrical excitation elucidates fundamental principles of atomic interaction and energy transformation. This complex relationship between electricity, atomic vibration, and radiated light encapsulates much of classical atomic theory while paving the way for further exploration into quantum properties of light emission.

References

• Einstein, A. (1905). Does the Inertia of a Body Depend Upon Its Energy Content? Annalen der Physik, 18(4), 639-641.
• Heisenberg, W. (1927). The Physical Principles of the Quantum Theory. Dover Publications.
• Kirchhoff, G. (1882). Die Grundzüge der Warmestrahlung. In thermodynamische Vorlesungen.
• Planck, M. (1901). On the Law of the Energy Distribution in the Normal Spectrum. Annalen der Physik, 4(3), 553-563.
• Wien, W. (1893). On the Sensible and Invisible Radiation. Annalen der Physik, 47(7), 681-706.
• Feynman, R.P. (1965). The Feynman Lectures on Physics. Volume I. Addison-Wesley.
• Scheck, F. (2008). Electricity and Magnetism. Springer.
• Griffiths, D.J. (2013). Introduction to Quantum Mechanics. Addison-Wesley.
• Taylor, J.R. (2005). Classical Mechanics. University Science Books.
• Hubbard, J. (2014). A Physics for the Humanities: Understanding the Universe. CreateSpace Independent Publishing Platform.