Question

what is magnitude in physical change

Answer 1

Definitely it does not changes with units. What changes is the numerals which denotes the magnitude. For example u have a stick in your hand whose length is 5 foot. U can also say that u have stick whose lenght is 150 cm. Length of stick is same just the numerals denoting the unit is changed...

Answer 2

Magnitude means unit.
Units are:-
Speed=Km/h
M/s
Distance=M,km etc.
Time=Sec/Min/hrs etc.
So, these are called units.