Question
Electromagnetic radiation with a maximum wavelength of \(540~nm~ (5.4×10^{−7}~ m)\) is needed for the study of the photoelectric effect in potassium atoms. What is the approximate frequency that corresponds to this wavelength?
A \( 1.8×10^{−15} s^{−1}\)
B \( 1.6×10^2 s^{−1}\)
C \(1.9×10^6 s^{−1}\)
D \( 5.6×10^{14} s^{−1}\)
▶️Answer/Explanation
Ans: D
c=λν (speed of light = wavelength × frequency),
so ν=c/λ.
\(ν=(2.998×10^8m/s)/(5.4×10^{−7}m)=5.6×10^{14} s^{−1}\).
Question
In an experiment on the photoelectric effect, a photon with a frequency of \(7\times 10^14s^{−1}\)
was absorbed by a sample. What is the approximate energy of this photon?
A \(5\times 10^{-19}\)
B \(1\times 10^{-15}\)
C \(2\times 10^{6}\)
D \(1\times 10^{48}\)
▶️Answer/Explanation
Ans: A
E=hν (energy = Planck’s constant × frequency), so
E\( = (6.626\times 10^{-34}Js)\times (7\times 10^{14}s^{-1})=5\times 10^{-19}J\)
Question
The frequency and energy ranges of photons in some parts of the electromagnetic spectrum are given in the table above. Which of the following could be the energy of a photon in the visible range?
A \(9\times 10^{-21}\)
B \(4\times 10^{-20}\)
C \(4\times 10^{-19}\)
D \(9\times 10^{-19}\)
▶️Answer/Explanation
Ans: C
The frequency and energy of light in the visible range are between those in the infrared and ultraviolet ranges. The upper limit for the IR region is \(3\times 10^{-19}\) J, and the lower limit for the ultraviolet region is \(5\times 10^{-19}\) J.
\(C_{25}H_{30}N^(aq)+OH^{-}(aq)\rightarrow C_{25}H_{30}N_{3}OH(aq)\)
violet colorless
Question
To choose a wavelength to analyze the progress of the reaction, a student records the absorbance spectra of both \(C_{25}H_{30}N_{3}^{+}\)(aq) and \(C_{25}H_{30}N_{3}OH\)(aq) in the range of 200-800 nm. The two spectra are presented in the graph below.
The student wants to use the spectrophotometer to measure \([C_{25}H_{30}N_{3}^{+}]\) with the greatest sensitivity as the reaction progresses. Which of the following indicates the best wavelength setting and explains why it is best?
(A) 205 nm, because the colorless form of the molecule will absorb significantly at this wavelength
(B) 205 nm, because both forms of the molecule will absorb significantly at this wavelength
(C) 590 nm, because only the violet form of the molecule will absorb significantly at this wavelength
(D) 590 nm, because this wavelength falls in the violet region of the visible light spectrum
▶️Answer/Explanation
Ans:C