When is a filepath neccessary using pandas when working with an excel file?

Question

I am trying to get into pandas and I am confused here is a program that reads from an excel file and it works without giving it a filepath when the excel file is in the same folder as the python program:

import pandas as pd

excel_file = "RandomExcelNumbers.xlsx"
xldata = pd.read_excel(excel_file, sheet_name= "Sheet1")

xl_Value1 = xldata["ColTitle2"][0]
print(xl_Value1)

Now I tried something different:

import pandas as pd

filename = "Test.xlsx"

def read_value_from_excel(filename, column="C", row=3):
    """Read a single cell value from an Excel file"""
    return pd.read_excel(filename, skiprows=row - 1, usecols=column, nrows=1, header=None, names=["Value"]).iloc[0]["Value"]

print(read_value_from_excel(filename, "C", 3))

and it gives me this error message: FileNotFoundError: [Errno 2] No such file or directory: 'Test.xlsx'

Please, what's the difference between these two programs? One needs the filepath, the other does not? Why is that? Is there a way to not neccessarily give the filepath in program no. 2 and let the program compile?

Thank you!