Transcript clicker questions 2

Consider two light fields in vacuum, one at 532 nm (green), the
other at 400 nm wavelength (blue). If you multiply the
wavelength  of each light field with the corresponding
frequency , the result will be …
(A) … a larger number for the green light field than for the blue
(B) … a smaller number for the green light field than for the blue
(C) … the same number for the green and the blue light
Consider two light fields in vacuum, one at 532 nm (green), the
other at 400 nm wavelength (blue). If you multiply the
wavelength  of each light field with the corresponding
frequency , the result will be …
(A) … a larger number for the green light field than for the blue
(B) … a smaller number for the green light field than for the blue
(C) … the same number for the green and the blue light
namely the speed of light:
c = ·
light
Photoelectric Effect
Assume that electrons are emitted from
the metal surface with some kinetic
energy Ekin. We now apply a positive voltage
U to the metal, holding the detector plate
at zero voltage. Which of the following
statements is correct?
detector
plate
electrons
metal
+V GND
(A) Positive voltage accelerates the electrons towards the detector
plate. We will measure a current independent of the voltage as long as it
is positive.
(B) The voltage has to be greater than Ekin in order to measure a
current. Otherwise, the kinetic energy of the electrons is too great,
the electrons will leave the setup and there will be no current.
(C) As long as the voltage U < Ekin/e, we will measure a current. Otherwise,
the positive voltage creates a force that “pulls” the electrons back into
the metal surface before they can reach the detector.
light
Photoelectric Effect
Assume that electrons are emitted from
the metal surface with some kinetic
energy Ekin. We now apply a positive voltage
U to the metal, holding the detector plate
at zero voltage. Which of the following
statements is correct?
detector
plate
electrons
metal
+V GND
(A) Positive voltage accelerates the electrons towards the detector
plate. We will measure a current independent of the voltage as long as it
is positive.
(B) The voltage has to be greater than Ekin in order to measure a
current. Otherwise, the kinetic energy of the electrons is too great,
the electrons will leave the setup and there will be no current.
(C) As long as the voltage U < Ekin/e, we will measure a current. Otherwise,
the positive voltage creates a force that “pulls” the electrons back into
the metal surface before they can reach the detector.
Photoelectric Effect
EM radiation can – under certain circumstances – knock electrons out
of molecules and surfaces. Imagine a clean calcium surface under vacuum,
and assume that you can somehow measure if electrons are emitted
from the surface.
Green light strikes the surface, and no electrons are emitted.
Could electrons possibly be emitted if you
(A) doubled the light intensity?
(B) used red light instead of green?
(C) used UV light instead of green?
(D) none of the above.
Photoelectric Effect
EM radiation can – under certain circumstances – knock electrons out
of molecules and surfaces. Imagine a clean calcium surface under vacuum,
and assume that you can somehow measure if electrons are emitted
from the surface.
Green light strikes the surface, and no electrons are emitted.
Could electrons possibly be emitted if you
(A) doubled the light intensity?
(B) used red light instead of green?
(C) used UV light instead of green?
(D) none of the above.
Light has the properties of ...
(A)… waves
(B)… particles
(C)… both
(D)... neither
Light has the properties of ...
(A)… waves
(B)… particles
(C)… both
(D)... neither