DuckieDai Coulomb's Law Python Program

physics · MIT License

Overview

Solve electric force, either charge magnitude, or separation distance using Coulomb's law and identify attraction or repulsion when charge signs are known.

Tested on a TI calculator
Downloaded 44 times
Version 1.0.0
5856 bytes
Uses math

Download COULOMB.py Read the source How to install

Before you run it

TI-84 Plus CE Python · tested on OS 5.8.3, Python App 5.8.3.0048
TI Connect CE .py conversion to a Python AppVar in RAM; physically verified one program at a time
Charges are treated as point charges and ke is 8.988E9.
Distance and force magnitudes must be positive; divisor values cannot be zero.
Force magnitude alone cannot determine an unknown charge's sign.

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Learn the math

How Coulomb's law works

The idea

Electric charges push or pull on each other. The force grows with the size of each charge and drops quickly as they move apart: twice the distance gives one quarter of the force.

Charges with the same sign repel. Charges with opposite signs attract.

The formula

Fe = ke*|q1*q2|/r^2

Fe: size of the electric force (N)
ke: 8.988 x 10^9 N*m^2/C^2, built into the program
q1, q2: the two charges in coulombs (C)
r: distance between the charges (m)

Using the program

Choose what to solve for: 1 force, 2 charge 1, 3 charge 2, or 4 distance.
Enter the known values. For a force calculation the program also tells you whether the force is attractive or repulsive.

Worked example

Two charges of 2 microcoulombs and 3 microcoulombs sit 0.5 m apart. Choose 1 and enter 0.000002, 0.000003, and 0.5.

The program shows Fe = 0.2157 newtons (it prints more decimal places) and Force type: REPULSIVE, because both charges are positive.

Tips and common mistakes

Convert microcoulombs to coulombs before typing: 1 microcoulomb is 0.000001 C.
Type a negative sign for a negative charge so the program can tell you the direction.
Distance is squared, so a small error in r makes a large error in the force.

Where this comes up

It opens the electricity unit in high school physics and second-semester college physics. General chemistry uses the same idea to explain ionic bonding and lattice energy.

Exact reviewed bytes

Source code

Download .py

View source below, copy it when JavaScript is available, or download the exact .py bytes.

"""DuckieDai Coulomb's Law for TI-84 Plus CE Python."""

from math import sqrt


def duckiedai_intro(program_name, wait=True):
    """Show the reusable DuckieDai program opening."""
    title = program_name[:16]
    empty = 16 - len(title)
    left = empty // 2
    right = empty - left

    print("+----------------------+")
    print("|   " + " " * left + title + " " * right + "   |")
    print("|                      |")
    print("|       __             |")
    print("|   ___(o )>  quack!   |")
    print("|   \\ <_. )           |")
    print("|    `---'             |")
    print("|     by DuckieDai     |")
    print("+----------------------+")
    print("Loading...")

    if wait:
        input("Press enter to start ")
        print("\n" * 6)


def number(prompt):
    """Allow positive or negative finite numbers."""
    while True:
        try:
            value = float(input(prompt))

            if value > -1e100 and value < 1e100:
                return value

        except ValueError:
            pass

        print("Enter a valid number.")


def nonzero_number(prompt):
    """Require a number other than zero."""
    while True:
        value = number(prompt)

        if value != 0:
            return value

        print("Value cannot be zero.")


def positive_number(prompt):
    """Require a number greater than zero."""
    while True:
        try:
            value = float(input(prompt))

            if value > 0 and value < 1e100:
                return value

        except ValueError:
            pass

        print("Enter a number above 0.")


def show_answer(name, value, unit):
    input("Press enter for answer ")
    print("\n" * 6)
    print("ANSWER")
    print(name + " = " + str(value))
    print(unit)


def force_type(q1, q2):
    """Tell whether two charges attract or repel."""
    if q1 * q2 < 0:
        return "ATTRACTIVE"
    else:
        return "REPULSIVE"


def main():
    duckiedai_intro("COULOMBS LAW")

    ke = 8.988e9

    print("COULOMB'S LAW")
    print()
    print("Formula:")
    print("Fe = ke*|q1*q2|/r^2")
    print()
    print("ke = 8.988E9")
    input("Press enter for menu ")
    print("\n" * 6)
    print()
    print("What do you need?")
    print()
    print("1. Electric force")
    print("2. Charge 1")
    print("3. Charge 2")
    print("4. Distance")
    print()

    choice = input("Choose 1-4: ")

    print()

    # ==========================================
    # 1. SOLVE ELECTRIC FORCE
    #
    # Fe = ke*|q1*q2|/r^2
    # ==========================================

    if choice == "1":

        q1 = nonzero_number("Charge 1 (C): ")
        q2 = nonzero_number("Charge 2 (C): ")
        r = positive_number("Distance (m): ")

        force = (
            ke * abs(q1 * q2) /
            (r ** 2)
        )

        print()
        print("Using:")
        print("Fe = ke*|q1*q2|/r^2")

        show_answer(
            "Fe",
            force,
            "newtons"
        )

        print()
        print("Force type:")
        print(force_type(q1, q2))

    # ==========================================
    # 2. SOLVE MAGNITUDE OF CHARGE 1
    #
    # |q1| = Fe*r^2 / (ke*|q2|)
    # ==========================================

    elif choice == "2":

        force = positive_number("Force (N): ")
        q2 = nonzero_number("Charge 2 (C): ")
        r = positive_number("Distance (m): ")

        q1 = (
            force * r ** 2 /
            (ke * abs(q2))
        )

        print()
        print("Using:")
        print("Fe = ke*|q1*q2|/r^2")
        print()
        print("Rearranged:")
        print("|q1| = Fe*r^2")
        print("       /(ke*|q2|)")

        show_answer(
            "|q1|",
            q1,
            "coulombs"
        )

        print()
        print("Note:")
        print("Force alone cannot")
        print("determine q1 sign.")

    # ==========================================
    # 3. SOLVE MAGNITUDE OF CHARGE 2
    #
    # |q2| = Fe*r^2 / (ke*|q1|)
    # ==========================================

    elif choice == "3":

        force = positive_number("Force (N): ")
        q1 = nonzero_number("Charge 1 (C): ")
        r = positive_number("Distance (m): ")

        q2 = (
            force * r ** 2 /
            (ke * abs(q1))
        )

        print()
        print("Using:")
        print("Fe = ke*|q1*q2|/r^2")
        print()
        print("Rearranged:")
        print("|q2| = Fe*r^2")
        print("       /(ke*|q1|)")

        show_answer(
            "|q2|",
            q2,
            "coulombs"
        )

        print()
        print("Note:")
        print("Force alone cannot")
        print("determine q2 sign.")

    # ==========================================
    # 4. SOLVE DISTANCE
    #
    # r = sqrt(ke*|q1*q2|/Fe)
    # ==========================================

    elif choice == "4":

        force = positive_number("Force (N): ")
        q1 = nonzero_number("Charge 1 (C): ")
        q2 = nonzero_number("Charge 2 (C): ")

        r = sqrt(
            ke * abs(q1 * q2) /
            force
        )

        print()
        print("Using:")
        print("Fe = ke*|q1*q2|/r^2")
        print()
        print("Rearranged:")
        print("r = sqrt(")
        print("ke*|q1*q2|/Fe)")

        show_answer(
            "r",
            r,
            "meters"
        )

        print()
        print("Force type:")
        print(force_type(q1, q2))

    else:
        print("Invalid choice.")

    print()
    print("DuckieDai says: done!")


# TI-Python imports the selected AppVar rather than
# setting __name__ to main.
main()

"""DuckieDai Coulomb's Law for TI-84 Plus CE Python."""
from math import sqrt
def duckiedai_intro(program_name, wait=True):
"""Show the reusable DuckieDai program opening."""
title = program_name[:16]
empty = 16 - len(title)
left = empty // 2
right = empty - left
print("+----------------------+")
print("| " + " " * left + title + " " * right + " |")
print("| |")
print("| __ |")
print("| ___(o )> quack! |")
print("| \\ <_. ) |")
print("| `---' |")
print("| by DuckieDai |")
print("+----------------------+")
print("Loading...")
if wait:
input("Press enter to start ")
print("\n" * 6)
def number(prompt):
"""Allow positive or negative finite numbers."""
while True:
try:
value = float(input(prompt))
if value > -1e100 and value < 1e100:
return value
except ValueError:
pass
print("Enter a valid number.")
def nonzero_number(prompt):
"""Require a number other than zero."""
while True:
value = number(prompt)
if value != 0:
return value
print("Value cannot be zero.")
def positive_number(prompt):
"""Require a number greater than zero."""
while True:
try:
value = float(input(prompt))
if value > 0 and value < 1e100:
return value
except ValueError:
pass
print("Enter a number above 0.")
def show_answer(name, value, unit):
input("Press enter for answer ")
print("\n" * 6)
print("ANSWER")
print(name + " = " + str(value))
print(unit)
def force_type(q1, q2):
"""Tell whether two charges attract or repel."""
if q1 * q2 < 0:
return "ATTRACTIVE"
else:
return "REPULSIVE"
def main():
duckiedai_intro("COULOMBS LAW")
ke = 8.988e9
print("COULOMB'S LAW")
print()
print("Formula:")
print("Fe = ke*|q1*q2|/r^2")
print()
print("ke = 8.988E9")
input("Press enter for menu ")
print("\n" * 6)
print()
print("What do you need?")
print()
print("1. Electric force")
print("2. Charge 1")
print("3. Charge 2")
print("4. Distance")
print()
choice = input("Choose 1-4: ")
print()
# ==========================================
# 1. SOLVE ELECTRIC FORCE
#
# Fe = ke*|q1*q2|/r^2
# ==========================================
if choice == "1":
q1 = nonzero_number("Charge 1 (C): ")
q2 = nonzero_number("Charge 2 (C): ")
r = positive_number("Distance (m): ")
force = (
ke * abs(q1 * q2) /
(r ** 2)
)
print()
print("Using:")
print("Fe = ke*|q1*q2|/r^2")
show_answer(
"Fe",
force,
"newtons"
)
print()
print("Force type:")
print(force_type(q1, q2))
# ==========================================
# 2. SOLVE MAGNITUDE OF CHARGE 1
#
# |q1| = Fe*r^2 / (ke*|q2|)
# ==========================================
elif choice == "2":
force = positive_number("Force (N): ")
q2 = nonzero_number("Charge 2 (C): ")
r = positive_number("Distance (m): ")
q1 = (
force * r ** 2 /
(ke * abs(q2))
)
print()
print("Using:")
print("Fe = ke*|q1*q2|/r^2")
print()
print("Rearranged:")
print("|q1| = Fe*r^2")
print(" /(ke*|q2|)")
show_answer(
"|q1|",
q1,
"coulombs"
)
print()
print("Note:")
print("Force alone cannot")
print("determine q1 sign.")
# ==========================================
# 3. SOLVE MAGNITUDE OF CHARGE 2
#
# |q2| = Fe*r^2 / (ke*|q1|)
# ==========================================
elif choice == "3":
force = positive_number("Force (N): ")
q1 = nonzero_number("Charge 1 (C): ")
r = positive_number("Distance (m): ")
q2 = (
force * r ** 2 /
(ke * abs(q1))
)
print()
print("Using:")
print("Fe = ke*|q1*q2|/r^2")
print()
print("Rearranged:")
print("|q2| = Fe*r^2")
print(" /(ke*|q1|)")
show_answer(
"|q2|",
q2,
"coulombs"
)
print()
print("Note:")
print("Force alone cannot")
print("determine q2 sign.")
# ==========================================
# 4. SOLVE DISTANCE
#
# r = sqrt(ke*|q1*q2|/Fe)
# ==========================================
elif choice == "4":
force = positive_number("Force (N): ")
q1 = nonzero_number("Charge 1 (C): ")
q2 = nonzero_number("Charge 2 (C): ")
r = sqrt(
ke * abs(q1 * q2) /
force
)
print()
print("Using:")
print("Fe = ke*|q1*q2|/r^2")
print()
print("Rearranged:")
print("r = sqrt(")
print("ke*|q1*q2|/Fe)")
show_answer(
"r",
r,
"meters"
)
print()
print("Force type:")
print(force_type(q1, q2))
else:
print("Invalid choice.")
print()
print("DuckieDai says: done!")
# TI-Python imports the selected AppVar rather than
# setting __name__ to main.
main()

Filename: COULOMB.py
Size: 5856 bytes
SHA-256: b569e112c44626a91e96f49630b52a1821bb5f1f996fc577b7c7a3e76eb47c2c

Usage

Inputs

Requested unknown: electric force, charge 1, charge 2, or distance
Known charges in coulombs and distance in metres

Outputs

Requested value and, when both charge signs are supplied, attractive or repulsive force type

Units: Charges use coulombs, distance uses metres, and force uses newtons.

Assumptions and limitations

Assumptions

Charges are treated as point charges and ke is 8.988E9.

Constraints

Distance and force magnitudes must be positive; divisor values cannot be zero.

Known failures

Force magnitude alone cannot determine an unknown charge's sign.
Inconsistent units produce an incorrect result.

Compatibility and review

Review status: Tested on a TI calculator
Tested on: TI-84 Plus CE Python; OS 5.8.3; Python App 5.8.3.0048; exact paginated .py transferred through TI Connect CE into RAM and tested individually
What happened: Passed: branded intro, paginated menu, Coulomb law workflow, force type output, and answer screen ran on the physical calculator
Dependencies: math
Suggested calculator name: COULOMB — you can give it another valid, unique name when you transfer it
Desktop test cases: Not available for this interactive-only source

This exact source auto-launches an interactive calculator session, so compatibility evidence comes from the recorded physical-device review rather than an importable desktop fixture.

Transfer and launch

Download the .py file, send it to your calculator with TI Connect CE as COULOMB or another name, then open the Python App and try the worked example on this page first.

Full installation and troubleshooting guide. Check your teacher's or exam's rules before using any program.

Version history

1.0.0 — current version, published 2026-09-23. Download this reviewed version

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