Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Problem of the 8th Experimental Physics Olympiad, Skopje, 8 May 2021
  Determination of Planck constant by LED   This is the problem of the 8$^\mathrm{th}$ International Experimental Physics
Olympiad (EPO). The task of the EPO8 is to determine Plank constant
$\hbar=h/2\pi$ using the given set-up with LED. If you have an idea how to do
it, do it and send us the result; skip the reading of the detailed step by step
instructions with increasing difficulties. We expect the participants to follow
the suggested items -- they are instructive for physics education in
general.Only the reading of historical remarks given in the first section can
be omitted during the Olympiad without loss of generality. Participants should
try solving as much tasks as they can without paying attention to the age
categories: give your best.

10
The categories of this paper are: q-bio
14
The categories of this paper are: math-ph
37
The categories of this paper are: supr-con
21
The categories of this paper are: adap-org
36
The categories of this paper are: cmp-lg
4
The categories of this paper are: cond-mat
34
The categories of this paper are: chem-ph
31
The categories of this paper are: ao-sci
2
The categories of this paper are: math
33
The categories of this paper are: plasm-ph
27
The categories of this paper are: comp-gas
23
The categories of this paper are: solv-int
0
The categories of this paper are: hep-ph
15
The categories of this paper are: nucl-ex
11
The categories of this paper are: hep-lat
1
The categories of this paper are: cs