The most common and most likely answer to this crossword clue is the 15 letter word ELECTRODYNAMICS
I've seen this crossword clue in Financial Times
E
L
E
C
T
R
O
D
Y
N
A
M
I
C
S
Buddy explains!
The straight part
We know that "part of physics syllabus" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case part of physics syllabus = electrodynamics.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ELECTRODYNAMICS mean?
ELECTRODYNAMICS noun- The phenomena associated with moving electric charges, and their interaction with electric and magnetic fields; the study of these phenomena.