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Q.37

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Physics For Scientists & Engineers
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Short Answer

a. What downward transitions are possible for a sodium atom in the 6s state?

b. What are the wavelengths of the photons emitted in each of these transitions?

(a) 6s 5p, 6s4p and 6s3p

(b) E=0.17 eV

See the step by step solution

Step by Step Solution

Diagram :

The allowed transitions are determined form the following usual selection rules

L=±1S=0J=0,±1

If the above selection rules are not satisfied, no other transitions are allowed between the energy levels.

The following diagram shows Ne3sground state of sodium atom and some are in excited state.

Part (a) Step 1:

The selection rule for a transition is

l=±1

Now for s state l=0. The transition is possible if the lower state has l value as 1 . But for 6s, there are possible lower states having l=1 are 5p,4p and 3p.

The possible transitions are,

6s5p, 6s4p and 6s 3p

Part (b) Step 2:

Wavelength of photon emitted is

λ=hcE

Rearranging the equation (1) for E.

E=hcλ ......(1)

Here, h is Plank's constant 4.14×10-15 eV.s and c is speed of light in vacuum 3×108 m/s.

The energy level difference in the transition, 6s5p is,

E=E6s-E5p

Substitute 4.51eV and E6s and 4.34eV for E5p in the above equation,

E=4.51 eV-4.34eV=0.17eV

Substituting values in above equation:

Substitute 4.14×10-15eV.s for h,3×108 m/s for c and 0.17eV for λ in the above equation.

localid="1649071820977" λ6s5p=4.14×10-15eVs3×108 m/s0.17eV=7300×10-9m109nm1.0m=7300 nm

Therefore the wavelength is 7300 nm

Energy level difference 2:

The energy level difference in the transition 6s4p is,

localid="1648557023475" E=E6s-E4p

Substitute 4.51eV for E6s and 3.75eV for E4p in the above equation.

E=E6s-E4p=4.51eV-3.75eV=0.76eV

Substitute localid="1648557182261" 4.14×10-15eV.s for h,3×108 m/s for c and 0.76eV for λ in the above equation.

localid="1648557427578" λ6s5p=4.14×10-15eVs3×108m/s0.7eV=1634×10-9m109nm/m=1634 nm

Therefore, the wavelength is 1634 nm.

Energy level difference 3:

The energy level difference in the transition 6s3p is,

E=E6s-E4p

Substitute 4.51eV for E5s and 2.104eV for E3p in the above equation.

localid="1648557169920" E=4.51eV-2.104eV=2.406eV

Substitute 4.14×10-15eV.s for h,3×108m/s for c and 2.406 eV for λ in the above equation.

λ6s5p=4.14×10-15eVs3×108m/s2.406 eV=516.2×10-9m109nm/m=516.2 nm

Therefore, the wavelength is 516.2 nm.

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