Static Electricity and Electric Forces Quiz

When a balloon is rubbed against dry hair, electrons are transferred from the hair to the balloon. This transfer occurs because the materials have different affinities for electrons, a phenomenon known as triboelectric charging. As the balloon gains extra electrons, it becomes negatively charged. In contrast, the hair loses electrons and becomes positively charged. Thus, the balloon acquires a negative charge due to the excess electrons it receives during the rubbing process.

Robert Millikan's research demonstrated that electric charge is not a continuous variable, but rather comes in fixed, indivisible units. His famous oil drop experiment provided evidence that the charge of an electron is a fundamental quantity, leading to the conclusion that all electric charge is a multiple of this elementary charge. This quantization means that charges can only exist in specific amounts rather than any arbitrary value, fundamentally altering our understanding of electricity and atomic structure.

When a negatively charged rod is brought near a neutral metal sphere, electrons in the sphere are repelled and move away from the rod, leaving behind a region of positive charge. This process is called induction. Once the rod is removed, the electrons return to their original positions, but since some have been repelled away, the sphere is left with a net positive charge. Thus, the metal sphere retains a positive charge after the negatively charged rod is taken away.

A neutral conductor can be charged by contact because it has no net charge, allowing it to gain or lose electrons when touched by a charged object. If the conductor were positively charged, it would repel positive charges and attract negative ones, preventing effective charging. If it were grounded, any excess charge would flow away, neutralizing the effect. Thus, only a neutral conductor can effectively interact with a charged object, allowing it to acquire a charge through the transfer of electrons.

According to Coulomb's law, the electric force between two charged objects is inversely proportional to the square of the distance between them. If the distance is decreased from r to 0.5r, the new force can be calculated as F' = k * (q1 * q2) / (0.5r)² = k * (q1 * q2) / (0.25r²) = 4 * (k * (q1 * q2) / r²), indicating that the force becomes four times stronger. Therefore, the force between the two objects becomes quadrapled when the distance is halved.

The electric force between two point charges is described by Coulomb's law, which states that the force is inversely proportional to the square of the distance between the charges. When the distance increases from 2 cm to 8 cm, the new distance is four times the original distance. Since the force is inversely proportional to the square of the distance, the force decreases by a factor of \(4^2 = 16\). Therefore, the new force is \(1/16\) of the original force. However, since the question specifies the factor change, it indicates that the force reduces to \(1/4\) of its original value based on the proportionality.

The force between two charges is given by Coulomb's law, which states that the force is directly proportional to the product of the magnitudes of the charges. If both charges double, the new force can be calculated as follows:

Initial force ∝ (q1 * q2)
New force ∝ (2q1 * 2q2) = 4(q1 * q2)

However, since both charges are doubled, we must also consider the increase in the force due to the second charge being increased from 14.0 x 10^-6 C to 28.0 x 10^-6 C, which results in an overall factor of 2 in addition to the initial doubling effect. Thus, the total increase in force becomes 4 (from the first charge) multiplied by 2 (from the second charge), resulting in an overall factor of 8.

Electric force is unique in that it can act in both attractive and repulsive ways, depending on the charges involved. Unlike gravitational force, which only attracts (as it always pulls masses together), electric force can either pull two opposite charges together or push two like charges apart. This dual nature of electric force allows for a wider range of interactions between charged particles, making it fundamentally different from gravitational force, which is always attractive.

The strength of an electric field generated by a charged object diminishes with increasing distance from the charge. According to Coulomb's law, the electric field strength is inversely proportional to the square of the distance from the charge. This means that as you move further away from the charged object, the influence of the electric field weakens significantly. Therefore, while the magnitude of the charge is crucial, the distance from the charge is equally important in determining the strength of the electric field.

In an electric field, the number of field lines is proportional to the magnitude of the charge. A larger charge generates a stronger electric field, which is represented by more lines in the diagram. Therefore, if charge b is greater than charge a, it will have more field lines emanating from it, indicating a stronger electric field compared to charge a. This visual representation helps illustrate the relationship between charge magnitude and electric field strength.

When a rubber rod is rubbed with fur, electrons are transferred from the fur to the rubber. This process, known as triboelectric charging, causes the rubber rod to gain extra electrons, resulting in a negative charge. The fur, having lost electrons, becomes positively charged. The gain of electrons increases the negative charge of the rubber rod, demonstrating the principle of charge transfer through friction.

Charging a conductor by bringing it near another charged object without direct contact is known as induction. In this process, the electric field of the charged object causes a redistribution of charges within the conductor. When the conductor is grounded, electrons can either flow into or out of the conductor, depending on the nature of the charged object nearby. This results in the conductor acquiring a net charge opposite to that of the nearby charged object, demonstrating the principle of electrostatic induction.

The superposition principle states that when multiple forces act on an object, the total force is the vector sum of all individual forces. In the context of charged objects, each charged object exerts a force on the other based on Coulomb's law. The resultant force on a specific charged object is determined by adding these individual forces together, demonstrating how the total effect arises from the combination of separate influences. This principle is fundamental in physics for analyzing systems with multiple interacting forces.

The electric force between two point charges is described by Coulomb's law, which states that the force is inversely proportional to the square of the distance between the charges. When the distance between the charges increases from 1 cm to 3 cm, the new distance is 3 times the original distance. Since the force is inversely proportional to the square of the distance, the factor by which the force changes is (1/3)² = 1/9. Thus, the electric force decreases by a factor of 1/9.

When the charge of each of the two identical charges is tripled, the electric force between them increases according to Coulomb's Law, which states that the force is directly proportional to the product of the charges. If each charge is increased from \( q \) to \( 3q \), the new force becomes \( F' = k \frac{(3q)(3q)}{r^2} = 9k \frac{q^2}{r^2} \). The original force was \( F = k \frac{q^2}{r^2} \). Thus, the new force is 9 times the original, but since the charges are tripled, the factor by which the force changes is 3.

Charging a grounded conductor by induction involves bringing a charged object near the conductor without direct contact. The presence of the charged object causes a redistribution of charges within the conductor, resulting in one side becoming positively charged and the other negatively charged. If the conductor is then grounded, electrons can flow to or from the ground, neutralizing the charge imbalance. Once the charged object is removed, the conductor retains a net charge. This process demonstrates how a conductor can be charged without direct contact, distinguishing it from conduction, polarization, and friction.

Iron can be charged by induction because it is a conductive material. When a charged object is brought near iron, it causes the electrons in the iron to redistribute, creating a separation of charges. This process does not require direct contact, allowing the iron to become charged. In contrast, materials like glass and wood are insulators and do not allow for the movement of electrons in this manner, making them unable to be charged by induction. Gold, while conductive, is not typically used in induction charging scenarios compared to iron.

A charged object generates an electric field in the space surrounding it, which represents the influence that the charge exerts on other charges in that area. This field indicates the direction and strength of the force that would be experienced by a positive test charge placed within it. Unlike electric force, which is the interaction between charges, the electric field is a property of the space around the charge itself, making it the correct answer.

Millikan's experiments, particularly his oil drop experiment, demonstrated that electric charge exists in discrete units rather than as a continuous spectrum. He observed that the charges on the oil droplets were always integer multiples of a smallest unit of charge, which is the charge of an electron. This finding provided strong evidence that electric charge is quantized, meaning it can only exist in specific amounts and cannot be divided into smaller fractions. This fundamental property has significant implications in physics, influencing our understanding of atomic structure and electromagnetic interactions.