diff --git a/physics/first_law_of_thermodynamics.py b/physics/first_law_of_thermodynamics.py
new file mode 100644
index 000000000000..0ece2092518d
--- /dev/null
+++ b/physics/first_law_of_thermodynamics.py
@@ -0,0 +1,173 @@
+"""
+________________________________________________________________________________________
+The first law of thermodynamics states that, when energy passes into or out of a system
+(as work, heat, or matter), the system's internal energy changes in accordance with the
+law of conservation of energy. This also results in the observation that, in an
+externally isolated system, even with internal changes, the sum of all forms of energy
+must remain constant, as energy cannot be created or destroyed.
+
+Check out the formula used to calculate this flux:
+ --------------
+ | Q = ΔU + W |
+ --------------
+
+Q = heat added or removed from the system.
+ΔU = variation of internal energy of the system.
+W = work done by the system on its surroundings.
+
+OBS: All units must be equal to each other.
+(Description adapted from https://en.wikipedia.org/wiki/Laws_of_thermodynamics )
+"""
+
+
+def __check_args(argument: float) -> None:
+    """
+    Check that the arguments are valid.
+    >>> __check_args(50.0)
+    >>> __check_args(-20)
+    >>> __check_args("50")
+    Traceback (most recent call last):
+        ...
+    TypeError: Invalid argument. Should be an integer or float.
+    """
+
+    # Ensure valid instance
+    if not isinstance(argument, (int, float)):
+        raise TypeError("Invalid argument. Should be an integer or float.")
+
+
+def __categorize_system(argument_value: float, argument_name: str) -> None:
+    """
+    Categorizes the system based on the work done, heat added/removed,
+    and internal energy variation.
+    >>> __categorize_system(0, "work")
+    The system is isochoric (constant volume).
+    >>> __categorize_system(50, "heat")
+    The system is endothermic (absorbing heat).
+    >>> __categorize_system(-20, "internal_energy_variation")
+    The internal energy of the system is decreasing. It cooling down.
+    >>> __categorize_system(10, "invalid")
+    Traceback (most recent call last):
+        ...
+    ValueError: Should be 'work', 'heat', or 'internal_energy_variation'.
+    """
+
+    if argument_name == "work":
+        if argument_value == 0:
+            print("The system is isochoric (constant volume).")
+        elif argument_value > 0:
+            print("The system is expanding.")
+        elif argument_value < 0:
+            print("The system is compressing.")
+
+    elif argument_name == "heat":
+        if argument_value == 0:
+            print("The system is adiabatic (no heat exchange).")
+        elif argument_value > 0:
+            print("The system is endothermic (absorbing heat).")
+        elif argument_value < 0:
+            print("The system is exothermic (releasing heat).")
+
+    elif argument_name == "internal_energy_variation":
+        if argument_value == 0:
+            print("The system is isothermic (constant internal energy)")
+        elif argument_value > 0:
+            print("The internal energy of the system is increasing. It heating up.")
+        elif argument_value < 0:
+            print("The internal energy of the system is decreasing. It cooling down.")
+
+    else:
+        raise ValueError("Should be 'work', 'heat', or 'internal_energy_variation'.")
+
+
+def work(heat: float, internal_energy_variation: float) -> float:
+    """
+    >>> work(50.0, -20.0)
+    The system is endothermic (absorbing heat).
+    The internal energy of the system is decreasing. It cooling down.
+    The system is expanding.
+    70.0
+    >>> work(50.0, 50.0)
+    The system is endothermic (absorbing heat).
+    The internal energy of the system is increasing. It heating up.
+    The system is isochoric (constant volume).
+    0.0
+    >>> work(-50.0, 20.0)
+    The system is exothermic (releasing heat).
+    The internal energy of the system is increasing. It heating up.
+    The system is compressing.
+    -70.0
+    """
+    __check_args(heat)
+    __check_args(internal_energy_variation)
+
+    __categorize_system(heat, "heat")
+    __categorize_system(internal_energy_variation, "internal_energy_variation")
+
+    work = heat - internal_energy_variation
+    __categorize_system(work, "work")
+    return round(work, 1)
+
+
+def heat(internal_energy_variation: float, work: float) -> float:
+    """
+    >>> heat(-20.0, 30.0)
+    The internal energy of the system is decreasing. It cooling down.
+    The system is expanding.
+    The system is endothermic (absorbing heat).
+    10.0
+    >>> heat(50.0, 0.0)
+    The internal energy of the system is increasing. It heating up.
+    The system is isochoric (constant volume).
+    The system is endothermic (absorbing heat).
+    50.0
+    >>> heat(20.0, -70.0)
+    The internal energy of the system is increasing. It heating up.
+    The system is compressing.
+    The system is exothermic (releasing heat).
+    -50.0
+    """
+    __check_args(internal_energy_variation)
+    __check_args(work)
+
+    __categorize_system(internal_energy_variation, "internal_energy_variation")
+    __categorize_system(work, "work")
+
+    heat = round(internal_energy_variation + work, 1)
+    __categorize_system(heat, "heat")
+    return heat
+
+
+def internal_energy_variation(heat: float, work: float) -> float:
+    """
+    >>> internal_energy_variation(50.0, 30.0)
+    The system is endothermic (absorbing heat).
+    The system is expanding.
+    The internal energy of the system is increasing. It heating up.
+    20.0
+    >>> internal_energy_variation(50.0, 0.0)
+    The system is endothermic (absorbing heat).
+    The system is isochoric (constant volume).
+    The internal energy of the system is increasing. It heating up.
+    50.0
+    >>> internal_energy_variation(-50.0, -70.0)
+    The system is exothermic (releasing heat).
+    The system is compressing.
+    The internal energy of the system is increasing. It heating up.
+    20.0
+    """
+    __check_args(heat)
+    __check_args(work)
+
+    __categorize_system(heat, "heat")
+    __categorize_system(work, "work")
+
+    internal_energy_variation = round(heat - work, 1)
+    __categorize_system(internal_energy_variation, "internal_energy_variation")
+    return internal_energy_variation
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()
diff --git a/physics/magnetic_flux.py b/physics/magnetic_flux.py
new file mode 100644
index 000000000000..99a7ca215fd5
--- /dev/null
+++ b/physics/magnetic_flux.py
@@ -0,0 +1,81 @@
+"""
+________________________________________________________________________________________
+Magnetic flux (Φ) is a scalar quantity that measures the number of magnetic field
+lines (B) that pass through a closed area (A). Furthermore, the magnetic flux depends
+on the angle formed between the magnetic field and the normal line (N) in area A.
+Check out the formula used to calculate this flux:
+ ------------
+ | Φ = B.A.cos(θ) |
+ ------------
+
+Φ = magnetic flux (weber (Wb) or tesla square meter (T.m²))
+B = magnetic field (tesla (T))
+A = area (square meter (m²))
+θ = angle between magnetic field and normal line (degrees (°))
+
+(Description adapted from https://en.wikipedia.org/wiki/Ideal_gas_law )
+"""
+
+from math import cos, radians
+
+
+def check_args(magnetic_field: float, area: float, angle: float) -> None:
+    """
+    Check that the arguments are valid
+    """
+
+    # Ensure valid instance
+    if not isinstance(magnetic_field, (int, float)):
+        raise TypeError("Invalid magnetic field. Should be an integer or float.")
+
+    if not isinstance(area, (int, float)):
+        raise TypeError("Invalid area. Should be an integer or float.")
+
+    if not isinstance(angle, (int, float)):
+        raise TypeError("Invalid angle. Should be an integer or float.")
+
+    # Ensure valid angle
+    if angle < 0 or angle > 180:
+        raise ValueError("Invalid angle. Range is 0-180 degrees.")
+
+    # Ensure valid magnetic field
+    if magnetic_field < 0:
+        raise ValueError("Invalid magnetic field. Should be a positive number.")
+
+    # Ensure valid area
+    if area < 0:
+        raise ValueError("Invalid area. Should be a positive number.")
+
+
+def magnetic_flux(magnetic_field: float, area: float, angle: float) -> float:
+    """
+    >>> magnetic_flux(50.0, 2, 0.0)
+    100.0
+    >>> magnetic_flux(50, 2, 60.0)
+    50.0
+    >>> magnetic_flux(0.5, 4.0, 90.0)
+    0.0
+    >>> magnetic_flux(1, 2.0, 180.0)
+    -2.0
+    >>> magnetic_flux(-1.0, 2.0, 30.0)
+    Traceback (most recent call last):
+        ...
+    ValueError: Invalid magnetic field. Should be a positive number.
+    >>> magnetic_flux(1.0, 'a', 30.0)
+    Traceback (most recent call last):
+        ...
+    TypeError: Invalid area. Should be an integer or float.
+    >>> magnetic_flux(1.0, -2.0, 30.0)
+    Traceback (most recent call last):
+        ...
+    ValueError: Invalid area. Should be a positive number.
+    """
+    check_args(magnetic_field, area, angle)
+    rad = radians(angle)
+    return round(magnetic_field * area * cos(rad), 1)
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()