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A hot bar of iron glows a dull red. Using our simple ball-spring model of a solid (Figure 8.23), answer the following questions,explaining in detail the processes involved. You will need to make some rough estimates of atomic properties based on prior work. (a) What is the approximate energy of the lowest-energy spectral emission line? Give a numerical value. (b) What is the approximate energy of the highest-energy spectral emission line? Give a numerical value. (c) What is the quantum number of the highest-energy occupied state? (d) Predict the energies of two other lines in the emission spectrum of the glowing iron bar. (Note: Our simple model is too simple-the actual spectrum is more complicated. However, this simple analysis gets at some important aspects of the phenomenon.)

Short Answer

Expert verified

(a) The approximate energy of the lowest-energy spectral emission line is2.5×10−20 J .

(b) The approximate energy of the highest-energy spectral emission line is 2.88×10−19 J.

(c) The quantum number of the highest energy occupied state is about 12.

(d) The energies of two other lines in the emission spectrum are5×10−20 J and7.5×10−20 J respectively.

Step by step solution

01

Significance of the energy

The energy is referred to as a qualitative property which is transferred from one object to another object. It can also not be destroyed nor created.

02

(a) Determination of the approximate energy of the lowest energy line

The lowest energy emission spectrum line mainly represents the jump from one to another vibrational energy. The energy required for melting the iron is the energy of the lowest energy emission spectrum line.

The equation of the lowest energy emission spectrum line is expressed as:

E=kT

Here,E is the lowest energy emission spectrum line,k is the Boltzmann constant andT is the iron’s melting point.

Substitute 1.38×10−23J/Kfork and1811‿é forT in the above equation.

E=(1.38×10−23J/K)(1811‿é)=2.5×10−20 J

Thus, the approximate energy of the lowest-energy spectral emission line is 2.5×10−20 J.

03

(b) Determination of the approximate energy of the highest energy line 

The red colour line from the diagram given in the question is the highest energy emission spectral line.

The equation of the energy of the highest emission spectral line is expressed as:

E1=hf

Here,E1 is the energy of the highest emission spectral line,h is the Planck’s constant andf is the red light’s frequency.

Substitute6.626×10−34​J⋅s forh and 435×10−12 s-1forf in the above equation.

E1=(6.626×10−34​J⋅s)(435×10−12 s-1)=2.88×10−19 J

Thus, the approximate energy of the highest-energy spectral emission line is 2.88×10−19 J.

04

(c) Determination of the quantum number 

The equation of the quantum number is expressed as:

N=E1E

Here,N is the quantum number.

Substitute the values in the above equation.

N=2.88×10−19 J2.5×10−20 J=11.52≈12

Thus, the quantum number of the highest energy occupied state is about 12.

05

(d) Determination of the prediction of energies

The equation of the energy of the first line in the emission spectrum is expressed as:

U1=E+E=2E

Here,U1 is the energy of the first line in the emission spectrum.

Substitute the values in the above equation.

U1=2×2.5×10−20 J=5×10−20 J

The equation of the energy of the second line in the emission spectrum is expressed as:

U2=E+2E=3E

Here,U2 is the energy of the second line in the emission spectrum.

Substitute the values in the above equation.

U2=3×2.5×10−20 J=7.5×10−20 J

Here, these calculations are accurate and also wild.

Thus, the energies of two other lines in the emission spectrum are5×10−20 J and7.5×10−20 J respectively.

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Most popular questions from this chapter

If you try to increase the energy of a quantum harmonics oscillator by adding an amount of energy 12hks/m, the energy doesn’t increase. Why not?

Consider a microscopic spring–mass system whose spring stiffness is50N/m, and the mass is4×10-26kg. (a) What is the smallest amount of vibrational energy that can be added to this system? (b) What is the difference in mass (if any) of the microscopic oscillator between being in the ground state and being in the first excited state? (c) In a collection of these microscopic oscillators, the temperature is high enough that the ground state and the first three excited states are occupied. What are possible energies of photons emitted by these oscillators?

What is the energy of the photon emitted by the harmonic oscillator with stiffness ks and mass m when it drops from energy level 5 to energy level 2?

Make a rough estimate of this uniform energy spacing in electron volts (where 1 eV=1.6×10−19 J). You will need to make some rough estimates of atomic properties based on prior work. For comparison with the spacing of these vibrational energy states, note that the spacing between quantized energy levels for "electronic" states such as in atomic hydrogen is of the order of several electron volts.

(b) List several photon energies that would be emitted if a number of these vibrational energy levels were occupied due to collisional excitation. To what region of the spectrum (x-ray, visible, microwave, etc.) do these photons belong? (See Figure 8.1 at the beginning of the chapter.)

The mean lifetime of a certain excited atomic state is 5 ns. What is the probability of the atom staying in this excited state for t=10 ns or more?

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