CEM 141 Exam 2 Questions and Answers Already Passed
Describe the relationship between the frequency, wavelength, and velocity (speed) of a wave. -
Answers velocity (speed of light) = wavelength (m) x frequency (Hz or s^-1)
Draw and compare two waves of different frequency, wavelength, or amplitude. - Answers
frequency: higher frequency if amplitudes are closer together, lower frequency if they're further
apart
wavelength: greater wavelength if amplitudes are further apart, shorter wavelength if waves are
closer together
amplitude: if the height of the wave increases, the amplitude is larger
Calculate any one (frequency, wavelength, or velocity) given the other two. Use appropriate units.
- Answers know c=lambda (wavelength) x weird v (frequency)
Rank electromagnetic radiation (visible, gamma ray, UV, radio wave, IR, microwave, X-ray) in
terms of energy, wavelength, or frequency. - Answers gamma rays, x rays, UV, visible light
(VIBGYOR), infrared, microwave, radio wave
left side: short wavelength, high frequency and energy
right side: long wavelength, low frequency and energy
Describe and identify experimental evidence for why electromagnetic radiation is a wave. -
Answers Double slit experiment: waves interfere with each other to give that striped pattern due
to constructive and destructive interference (which happens in waves)
Make an argument (include claim, evidence, and reasoning) about why we can consider
electromagnetic radiation as a wave. - Answers Electromagnetic radiation is a wave and we can
see this through the double slit experiment. Waves of light were shown upon a barrier, and as
they passed through each slit, they diffracted, which caused both constructive and destructive
interference. Due to this, the constructed/destructed waves made a striped pattern on the back
surface of the experiment. Since waves have constructive and destructive interference, we can
conclude that electromagnetic radiation (light) is a wave.
Describe and identify experimental evidence for why electromagnetic radiation is a particle. -
Answers Many metals emit electrons when electromagnetic radiation shines on the surface.
The light is transferring energy to the electrons at the metal's surface where it is transformed
into kinetic energy that gives the electrons enough energy to leave the atoms in the metal. Only
lights with higher frequencies allow for an electron to be ejected. If you increase the intensity of
that light, more electrons will fly off, however, if lower frequency light that does not cause the
metal to emit an electron are shone on the metal, no matter how intense, the metal will never
, emit an electron. If electromagnetic radiation was only a wave, increasing the intensity of any
light would cause an electron to be emitted from the metal. This is how we know
electromagnetic radiation is a particle.
Using the photoelectric effect experiment, draw and explain graphs that show the number of
electrons ejected vs. frequency or wavelength of radiation that shines on the metal. - Answers
purple/blue lights will eject electrons while red light will not
Calculate the energy of photons of a given frequency or wavelength (and vice versa). - Answers
E= h (constant) x v (frequency)
Explain why the existence of photons (quantized light energy) explains the photoelectric effect. -
Answers because the threshold frequency is the minimum energy required to emit an electron; if
photons do not have enough energy to emit an electron, an electron will not be emitted
regardless of intensity
Make an argument (include claim, evidence, and reasoning) about why we can consider
electromagnetic radiation as a particle. - Answers Many metals emit electrons when
electromagnetic radiation shines on the surface. The light is transferring energy to the electrons
at the metal's surface where it is transformed into kinetic energy that gives the electrons
enough energy to leave the atoms in the metal. Only lights with higher frequencies allow for an
electron to be ejected. If you increase the intensity of that light, more electrons will fly off,
however, if lower frequency light that does not cause the metal to emit an electron are shone on
the metal, no matter how intense, the metal will never emit an electron. If electromagnetic
radiation was only a wave, increasing the intensity of any light would cause an electron to be
emitted from the metal. This is how we know electromagnetic radiation is a particle.
Explain how (and why) different atoms emit different wavelengths of light. - Answers each
element has electrons of different energies; the energy changes between the energy levels are
also different, so each element will have a different emission and absorption spectra
Compare and contrast atomic emission and absorption spectra and how they are generated. -
Answers Emission spectrum: generated by the hot gas of an element going through a prism;
forms black spectrum with only a few lines of light
Absorption spectrum: generated by a light shining on a hot gas of an element going through a
prism; form almost a full spectrum with only a few lines of light missing (lines missing are the
same found in the emission spectrum)
Use spectra to identify the presence of elements (by comparison, not calculation). - Answers
absorption and emission spectra are inversely related
Make an argument for why spectra are direct evidence for the existence of quantized energy
levels in an atom. - Answers Spectra are the direct evidence for the existence of quantized
energy levels in an atom because both atomic absorption and emission spectra show light of
Describe the relationship between the frequency, wavelength, and velocity (speed) of a wave. -
Answers velocity (speed of light) = wavelength (m) x frequency (Hz or s^-1)
Draw and compare two waves of different frequency, wavelength, or amplitude. - Answers
frequency: higher frequency if amplitudes are closer together, lower frequency if they're further
apart
wavelength: greater wavelength if amplitudes are further apart, shorter wavelength if waves are
closer together
amplitude: if the height of the wave increases, the amplitude is larger
Calculate any one (frequency, wavelength, or velocity) given the other two. Use appropriate units.
- Answers know c=lambda (wavelength) x weird v (frequency)
Rank electromagnetic radiation (visible, gamma ray, UV, radio wave, IR, microwave, X-ray) in
terms of energy, wavelength, or frequency. - Answers gamma rays, x rays, UV, visible light
(VIBGYOR), infrared, microwave, radio wave
left side: short wavelength, high frequency and energy
right side: long wavelength, low frequency and energy
Describe and identify experimental evidence for why electromagnetic radiation is a wave. -
Answers Double slit experiment: waves interfere with each other to give that striped pattern due
to constructive and destructive interference (which happens in waves)
Make an argument (include claim, evidence, and reasoning) about why we can consider
electromagnetic radiation as a wave. - Answers Electromagnetic radiation is a wave and we can
see this through the double slit experiment. Waves of light were shown upon a barrier, and as
they passed through each slit, they diffracted, which caused both constructive and destructive
interference. Due to this, the constructed/destructed waves made a striped pattern on the back
surface of the experiment. Since waves have constructive and destructive interference, we can
conclude that electromagnetic radiation (light) is a wave.
Describe and identify experimental evidence for why electromagnetic radiation is a particle. -
Answers Many metals emit electrons when electromagnetic radiation shines on the surface.
The light is transferring energy to the electrons at the metal's surface where it is transformed
into kinetic energy that gives the electrons enough energy to leave the atoms in the metal. Only
lights with higher frequencies allow for an electron to be ejected. If you increase the intensity of
that light, more electrons will fly off, however, if lower frequency light that does not cause the
metal to emit an electron are shone on the metal, no matter how intense, the metal will never
, emit an electron. If electromagnetic radiation was only a wave, increasing the intensity of any
light would cause an electron to be emitted from the metal. This is how we know
electromagnetic radiation is a particle.
Using the photoelectric effect experiment, draw and explain graphs that show the number of
electrons ejected vs. frequency or wavelength of radiation that shines on the metal. - Answers
purple/blue lights will eject electrons while red light will not
Calculate the energy of photons of a given frequency or wavelength (and vice versa). - Answers
E= h (constant) x v (frequency)
Explain why the existence of photons (quantized light energy) explains the photoelectric effect. -
Answers because the threshold frequency is the minimum energy required to emit an electron; if
photons do not have enough energy to emit an electron, an electron will not be emitted
regardless of intensity
Make an argument (include claim, evidence, and reasoning) about why we can consider
electromagnetic radiation as a particle. - Answers Many metals emit electrons when
electromagnetic radiation shines on the surface. The light is transferring energy to the electrons
at the metal's surface where it is transformed into kinetic energy that gives the electrons
enough energy to leave the atoms in the metal. Only lights with higher frequencies allow for an
electron to be ejected. If you increase the intensity of that light, more electrons will fly off,
however, if lower frequency light that does not cause the metal to emit an electron are shone on
the metal, no matter how intense, the metal will never emit an electron. If electromagnetic
radiation was only a wave, increasing the intensity of any light would cause an electron to be
emitted from the metal. This is how we know electromagnetic radiation is a particle.
Explain how (and why) different atoms emit different wavelengths of light. - Answers each
element has electrons of different energies; the energy changes between the energy levels are
also different, so each element will have a different emission and absorption spectra
Compare and contrast atomic emission and absorption spectra and how they are generated. -
Answers Emission spectrum: generated by the hot gas of an element going through a prism;
forms black spectrum with only a few lines of light
Absorption spectrum: generated by a light shining on a hot gas of an element going through a
prism; form almost a full spectrum with only a few lines of light missing (lines missing are the
same found in the emission spectrum)
Use spectra to identify the presence of elements (by comparison, not calculation). - Answers
absorption and emission spectra are inversely related
Make an argument for why spectra are direct evidence for the existence of quantized energy
levels in an atom. - Answers Spectra are the direct evidence for the existence of quantized
energy levels in an atom because both atomic absorption and emission spectra show light of
