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What is Coulomb's Law (Basic)?
Grade Level:
Class 10
AI/ML, Physics, Biotechnology, Space Technology, Chemistry, Engineering, Medicine
Definition
What is it?
Coulomb's Law tells us how strong the electrical force is between two charged objects, like two tiny magnets or charged balloons. It states that this force depends on how much charge each object has and how far apart they are.
Simple Example
Quick Example
Imagine you have two small, positively charged balloons. If you bring them close, they will push each other away. Coulomb's Law helps us calculate exactly how hard they push, depending on their charges and the distance between them. If you make one balloon's charge double, the push also doubles.
Worked Example
Step-by-Step
QUESTION: Two point charges, q1 = +2 microcoulombs (uC) and q2 = +3 microcoulombs (uC), are placed 0.03 meters (3 cm) apart in air. Calculate the electrostatic force between them. (Given: Coulomb's constant, k = 9 x 10^9 Nm^2/C^2)
STEP 1: Identify the given values.
q1 = +2 uC = 2 x 10^-6 C
q2 = +3 uC = 3 x 10^-6 C
r = 0.03 m
k = 9 x 10^9 Nm^2/C^2
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STEP 2: Write down Coulomb's Law formula.
F = k * |q1 * q2| / r^2
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STEP 3: Substitute the values into the formula.
F = (9 x 10^9) * |(2 x 10^-6) * (3 x 10^-6)| / (0.03)^2
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STEP 4: Calculate the product of charges.
|q1 * q2| = |(2 x 10^-6) * (3 x 10^-6)| = 6 x 10^-12 C^2
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STEP 5: Calculate the square of the distance.
r^2 = (0.03)^2 = 0.0009 m^2
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STEP 6: Substitute these back into the force equation and calculate.
F = (9 x 10^9) * (6 x 10^-12) / 0.0009
F = (54 x 10^-3) / 0.0009
F = 0.054 / 0.0009
F = 60 N
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STEP 7: Determine the nature of the force.
Since both charges are positive, the force is repulsive.
ANSWER: The electrostatic force between the charges is 60 Newtons (N) and is repulsive.
Why It Matters
Understanding Coulomb's Law is crucial for designing almost all electronic devices, from your smartphone to medical equipment. Engineers use it to create microchips, and scientists in biotechnology use it to study how molecules interact. It's fundamental to careers in electrical engineering, materials science, and even space technology for satellite components.
Common Mistakes
MISTAKE: Forgetting to convert units, especially microcoulombs (uC) to coulombs (C) or centimeters (cm) to meters (m). | CORRECTION: Always convert all given values to standard SI units (Coulombs for charge, meters for distance) before applying the formula.
MISTAKE: Not squaring the distance (r) in the denominator of the formula. | CORRECTION: Remember the formula is F = k * q1q2 / r^2. The '2' on the 'r' is important!
MISTAKE: Confusing attractive and repulsive forces, or using negative signs for charges in the magnitude calculation. | CORRECTION: The formula F = k * |q1q2| / r^2 calculates the magnitude (strength) of the force. Use the signs of the charges (like charges repel, opposite charges attract) to determine the direction of the force separately.
Practice Questions
Try It Yourself
QUESTION: Two charges, q1 = +1 C and q2 = -1 C, are placed 1 meter apart. What is the magnitude of the force between them? (k = 9 x 10^9 Nm^2/C^2) | ANSWER: 9 x 10^9 N
QUESTION: If the distance between two charges is doubled, how does the electrostatic force between them change? (Assume charges remain constant). | ANSWER: The force becomes one-fourth (1/4) of its original value.
QUESTION: Two identical charges repel each other with a force of 10 N when they are 0.01 m apart. What is the magnitude of each charge? (k = 9 x 10^9 Nm^2/C^2) | ANSWER: Approximately 1.05 x 10^-7 C
MCQ
Quick Quiz
Which of the following statements about Coulomb's Law is TRUE?
The electrostatic force is directly proportional to the distance between charges.
The electrostatic force is inversely proportional to the square of the distance between charges.
The electrostatic force is inversely proportional to the product of the charges.
The electrostatic force is independent of the medium between the charges.
The Correct Answer Is:
B
Coulomb's Law states that force is inversely proportional to the square of the distance (F proportional to 1/r^2). Options A and C are incorrect as force is directly proportional to the product of charges. Option D is incorrect as the medium affects the force (represented by 'k').
Real World Connection
In the Real World
In India, understanding Coulomb's Law is vital for the electronics industry, from making LED TVs to electric vehicle components. For example, the tiny transistors in your mobile phone's processor rely on precise control of electrostatic forces between charged particles. Even ISRO scientists use this principle when designing sensitive equipment for satellites, ensuring components interact correctly in the vacuum of space.
Key Vocabulary
Key Terms
ELECTROSTATIC FORCE: The attractive or repulsive force between electrically charged objects. | CHARGE: A fundamental property of matter that causes it to experience a force when placed in an electromagnetic field. | COULOMB (C): The SI unit of electric charge. | PERMITTIVITY: A measure of how an electric field affects, and is affected by, a dielectric medium. | REPULSION: A force that pushes objects apart.
What's Next
What to Learn Next
Great job learning about Coulomb's Law! Next, you should explore the concept of Electric Field. It builds directly on Coulomb's Law by explaining how a single charge creates a 'field' around it, which then exerts a force on any other charge placed in that field. This will help you understand more complex electrical interactions!
