PRELAB Lab 11: Atomic Physics Leaming objectives: AP1: Explain how experimental

Question

PRELAB Lab 11: Atomic Physics Leaming objectives: AP1: Explain how experimental data supports or rejects historical models of the atom. Questions from Active Learning Guide-2 points per question NOTE: For "observations" refer to images in lecture from 11/15 (Ch27-1) 27.1.1 Observe and explain In the late 19th century, severa observational facts had been established that any model of the atom had to explain. One included observations of light emitted by low-density gases. The experimental set up for these observations looks as follows: A glass tube filled with gas has two metal electrodes in it. The electrodes are connected to the poles of a high-voltage power supply. When the power is on, the gas in the tube glows. Different gases glow with different colors. a. Use a spectroscope (or a simple grating) to examine light emitted by a tube filled with hydrogen. Describe your observations b. Compare your observations to observations of the light of a bright lightbulb filament when viewed through the spectroscope. c. Use your understanding of energy transformations with the atoms (and photons) to explain the observations in parts a and b. Note that you should have two slightly different explanations since there are two different observations.

Explanation / Answer

a)

The applied high voltage would ionize the gas in the tube. This ionization causes an electric field within the electrodes of the tube and we see the current passing from one electrode to the other. We see a beam of light passing through one end to other end of the tube. The spectrograph or grating would help to determine the wavelength of the discharged light.

b)

The emission from a heavy light bulb is called thermoinc emission. When current pass through a thin filament, it is heated and the energy emitted in the form of light of specific wavelength. we can use the grating to determine the wavelength of the emission.

c)

In the first case, the electrons in the atom take sufficient energy from the power source and they jump off the atom (ionization) and then a bam of electrons travel from one electrode to the other while thermoinic emission is different case.

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