PHY3702 Assignment 1 Complete Solutions UNISA 2026 Quantum Physics

PHY3702
ASSIGNMENT 1
Quantum Physics

FULL SOLUTIONS
COMPLETE SOLUTIONS

MEMORANDUM
UNISA 2026

Page 1 of 21

,SOLUTIONS:

Question 1

(a) Using the Stefan–Boltzmann law for a blackbody,

𝐼 = 𝜎𝑇 4



where 𝜎 = 5.67 × 10−8 W m−2 K −4 and 𝐼 = 575 × 106 W m−2,
1/4
𝐼 1/4 575 × 106
𝑇=( ) =( ) = (1.014 × 1016 )1/4 ≈ 1.00 × 104 K.
𝜎 5.67 × 10−8



The surface temperature is approximately 1.0 × 104 K.

Using the Stefan–Boltzmann law 𝐼 = 𝜎𝑇 4 , with 𝐼 = 575 × 106 W m−2 and 𝜎 =
5.67 × 10−8 W m−2 K−4 ,

1/4
575 × 106
𝑇=( ) ≈ 1.78 × 104 K
5.67 × 10−8


2.898×10−3
Using Wien’s law 𝜆max = ,
𝑇

2.898 × 10−3
𝜆max ≈ ≈ 1.63 × 10−7 m = 163 nm
1.78 × 104




Page 2 of 21

, SOLUTIONS:

Question 2

(a) The photoelectric equation:

ℎ𝑐
𝑒𝑉0 = −𝜙
𝜆



With 𝑉0 = 1.2 V and 𝜆 = 480 nm:

ℎ𝑐 1240 eV nm
= ≈ 2.583 eV.
𝜆 480 nm
𝜙 = 2.583 eV − 1.2 eV = 1.383 eV.



The work function is 1.38 eV.

Photon energy:

ℎ𝑐 1240
𝐸= = ≈ 2.58 eV
𝜆 480


Work function:

𝜙 = 𝐸 − 𝑒𝑉𝑠 = 2.58 − 1.2 = 1.38 eV




Page 3 of 21