CMY 383: Spectroscopy (SR) Actual Questions And Correct Detailed Answers.
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Describe electromagnetic radiation - correct answer 1. Electron radiations are released as photons
2. Quantized harmonic waves travel at the speed of light
3. Electric and magnetic waves are perpendicular to each other
4. Transition between the states induc...
Describe electromagnetic radiation - correct answer 1. Electron radiations are
released as photons
2. Quantized harmonic waves travel at the speed of light
3. Electric and magnetic waves are perpendicular to each other
4. Transition between the states induced by electromagnetic radiation: M + hν → M*
Describe the Wave nature of a beam of single-frequency electromagnetic radiation - correct answer
1. a plane-polarized wave is shown propagating along the x-axis.
2. The electric field oscillates in a plane perpendicular to the magnetic field.
3. If the radiation were unpolarized, a component of the electric field would be seen in all planes.
Describe Wave Characteristics - correct answer 1. Amplitude (A): of the wave is the
length of the electric field vector at the wave maximum
2. Period (p): The time in seconds required for the passage of successive maxima or minima through a
fixed point in space
3. The frequency (v): is the number of oscillations of the field that occur per second and is equal to 1/p
4. The wavelength (y^) is the linear distance between any two equivalent points on successive waves
(e.g., successive maxima or minima)
5. velocity of propagation (v)i in meters per second: νi x yi
Describe the electromagnetic spectrum - correct answer 1. Radiowaves (NMR):
Excitation of nuclear spin states,
2. Microwaves: Excitation of rotational energy states
3. Infrared (IR): Excitation of vibrational energy states, i.e. stretching and bending of chemical bonds
e.g., organic functional groups.
4. UV-Vis: Excitation of electronic energy states, e.g. π-π* transition
Describe polarization of radiation - correct answer 1. Polarized radiation:
, - a beam of monochromatic radiation can be visualized as an infinite set of electric vectors that fluctuate
in length from zero to a maximum amplitude
2. Unpolarized radiation:
- electric vectors are viewed at various times during the passage of one wave of monochromatic
radiation through a fixed point in space.
3. Plane polarized radiation:
- the electric vectors are at the instant the wave is at its maximum.
- The vector in any one plane, e.g. XY, can be resolved into two mutually perpendicular components AB
and CD
- Removal of one of the two resultant planes of vibration produces a beam that is plane-polarized.
- The resultant electric vector of a plane-polarized beam then occupies a single plane.
Describe the processes happening in a Milikan's photoelectric experiment and the results obtained
thereof. - correct answer 1. a vacuum phototube circuit was used to study the
photoelectric effect
2. The surface of the large photocathode is usually coated with an alkali metal or one of its compounds.
3. When monochromatic radiation impinges on the photocathode, electrons are emitted from its surface
with a range of kinetic energies.
4. As long as the voltage V applied between the anode and the cathode is positive, the electrons are
drawn from left to right through the phototube to produce a current I in the circuit.
5. When the voltage across the phototube is adjusted so that the anode is slightly negative with respect
to the cathode, the photoelectrons are repelled by the anode, and the photocurrent decreases as
expected.
6. At this point in the experiment, however, some of the electrons have sufficient kinetic energy to
overcome the negative potential applied to the anode, and a current is still observed.
7. This experiment may be repeated for phototubes with different materials coating the photocathode.
8. In each experiment, the photocurrent is measured as a function of the applied voltage, and the
voltage V0 at which the photocurrent becomes precisely zero is noted.
9. The negative voltage at which the photocurrent is zero is called the stopping voltage.
10. It corresponds to the potential at which the most energetic electrons from the cathode are just
repelled from the anode.
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