CUET UG Physics Booster Test – 1 Fundamentals of Electric Charge

The term electricity is derived from the Greek word "elektron", meaning amber. The observation that rubbed amber attracts light objects was made by Thales of Miletus around 600 BC. Benjamin Franklin's major contribution was introducing the convention of positive and negative charges, not coining the word electricity. Therefore, Option C is incorrect and is the correct answer to this question. The remaining options accurately describe the historical development of the concept of electricity as discussed in NCERT. The discovery of frictional electrical effects through rubbing materials was known long before Franklin's work and forms the foundation of electrostatics.

The word electricity originates from the Greek word "elektron," meaning amber. Ancient Greeks noticed that amber attracted small objects after rubbing. This observation eventually led to the development of the science of electricity. Statement 2 is therefore correct. Statement 1 is incorrect because the origin is Greek, not Latin. Statement 3 is incorrect because Thales observed the phenomenon but did not propose the term. Statement 4 is incorrect because the word has no relation to wool. Hence only Statement 2 is correct, making Option B the correct answer according to NCERT.

When a glass rod is rubbed with silk, it loses electrons and becomes positively charged. A plastic rod rubbed with fur gains electrons and becomes negatively charged. Therefore, these oppositely charged objects attract each other, giving 1-a. Two glass rods rubbed with silk acquire similar positive charges and repel each other, giving 2-d. Plastic rubbed with fur and the fur acquire opposite charges and attract each other, giving 3-b. The remaining pair is 4-c. The question is based on NCERT's discussion of frictional electricity and the fundamental law that like charges repel while unlike charges attract. The matching sequence in Option A correctly represents all interactions.

Lightning is a natural example of electrical discharge occurring in the atmosphere. Static shocks experienced while touching a car door occur because accumulated charges suddenly discharge. Charges often build up due to rubbing of insulating surfaces. However, Statement 1 is incorrect because sparks from synthetic clothes are more common in dry weather, not humid weather. Moisture in humid air allows charges to leak away, reducing static buildup. Therefore Statements 2, 3, and 4 are correct, making Option D the correct answer according to NCERT principles of electrostatics.

The net charge of a system is obtained by adding all charges algebraically. Here: (+2e) + (-3e) + (+4e) + (-5e) + (+1e) = 2e - 3e + 4e - 5e + 1e = -1e Thus the system possesses a net negative charge equal to -1e. The calculation demonstrates the additive nature of electric charge and the principle of charge conservation. Since the total negative charge exceeds the total positive charge by one elementary charge, the resultant charge is -1e.

Polarity refers to the nature of electric charge possessed by a body, namely positive or negative. It helps distinguish the two kinds of charges and determines the interaction between charged objects. According to NCERT, like charges repel each other while unlike charges attract each other. Thus, polarity directly governs electrostatic interactions. It has no relation to the mass of an object or the rate of charge loss. Also, glass rubbed with silk and plastic rubbed with fur acquire opposite charges, not the same polarity. Therefore, Option B correctly describes the significance of charge polarity.

Initially, sphere A has 10 µC charge and sphere B is uncharged. Since the spheres are identical, charge is equally shared after contact. Each sphere gets: 10 µC ÷ 2 = 5 µC Applying Coulomb's law: F = kq₁q₂/r² = (9 × 10⁹)(5 × 10⁻⁶)(5 × 10⁻⁶)/(0.1)² = 22.5 N Both spheres carry positive charge after separation, so the force is repulsive. The calculation directly follows Coulomb's law and the principle of equal charge distribution among identical conductors.

One of the most basic observations in electrostatics is that two bodies carrying charges of the same type repel each other, while bodies carrying opposite charges attract each other. This principle forms the basis for the classification of electric charges into positive and negative types. The law is supported by numerous experiments involving charged rods, electroscopes, and Coulomb's investigations. NCERT emphasizes this interaction as a fundamental property of electric charge. Therefore, Option D correctly represents the behavior of charged bodies.

During electrification by rubbing, no new charge is created. Instead, electrons are transferred from one body to another. The total charge of the isolated system remains conserved, so the algebraic sum of charges remains zero. Only a very small fraction of the total electrons present in the bodies participates in the transfer process. Statement 2 is incorrect because the two bodies acquire equal and opposite charges, not like charges. Therefore, Statements 1, 3, and 4 are correct, making Option A the correct answer.

In the process of rubbing two solids, electrons that are loosely bound to atoms can move from one body to another. Protons remain fixed inside atomic nuclei and are not transferred during ordinary charging processes. When a body gains electrons, it acquires an excess of negative charge and becomes negatively charged. Therefore, Statements 2 and 3 are correct. Statements 1 and 4 are incorrect because protons do not migrate between bodies during frictional charging. Thus, Option B correctly describes the electron transfer mechanism discussed in NCERT.

Matter consists of atoms that are normally electrically neutral because they contain equal amounts of positive and negative charges. Therefore, Statement 1 is correct. A neutral object does contain charges; however, the total positive and negative charges are balanced, making Statement 2 incorrect. Statement 3 is correct because neutrality arises from exact charge balance. When a body becomes charged, this balance is disturbed due to gain or loss of electrons, making Statement 4 correct. Hence Statements 1, 3, and 4 are correct, and Option B is the correct answer according to NCERT.

When two bodies carrying equal and opposite charges are brought into contact, their charges neutralize each other. This process removes the electrostatic effects produced by the charges. Thus, Statements A and B correctly describe charge neutralization. Benjamin Franklin used such observations to introduce the terminology of positive and negative charges, making Statement D correct. Statement C is incorrect because unlike charges do not amplify each other on contact; instead, they cancel or neutralize each other. Therefore, Option C is the incorrect statement and hence the correct answer.

The proton possesses a positive elementary charge equal to +e, while the electron possesses a negative elementary charge equal to -e. Both have equal magnitudes but opposite signs. This is one of the fundamental concepts in atomic structure and electrostatics. The equality in magnitude of proton and electron charge explains why atoms remain electrically neutral when the number of protons equals the number of electrons. Therefore, Option C correctly represents the charges of protons and electrons.

A neutral conductor has equal positive and negative charges initially. If x electrons are removed from the conductor, the conductor loses negative charge. As a result, there is an excess of positive charge equal to x elementary charges. Therefore, the net charge developed on the conductor is +xe. The value does not depend on the total number of electrons originally present; it depends only on the number removed. Hence, Option A correctly describes the resulting charge on the conductor.

A gold-leaf electroscope is used to detect the presence of electric charge. When charge is transferred to the metal knob, it spreads through the conducting rod to the gold leaves. Both leaves acquire charges of the same sign and repel each other, causing divergence. The extent of divergence provides an indication of the amount of charge present. However, the instrument does not measure charge accurately in coulombs. The metal rod is a conductor, not an insulator. Therefore, Option D correctly explains the operation of a gold-leaf electroscope.

In a gold-leaf electroscope, the divergence of the leaves depends on the amount of charge present. A greater charge produces stronger repulsion between the leaves, leading to larger divergence. Therefore, Statement 1 is correct. When a charged body touches the knob, charge is transferred through the conducting rod to the leaves, making Statement 3 correct. Statement 2 is incorrect because larger divergence indicates greater, not smaller, charge. Statement 4 is also incorrect because the leaves acquire charges of the same sign, causing repulsion. Hence, Statements 1 and 3 are correct, making Option A the correct answer.

Since the copper piece is electrically neutral, the total positive charge must equal the total negative charge in magnitude. The magnitude of the positive charge is: Q = Ne = (2.5 × 10²⁴)(1.6 × 10⁻¹⁹) = 4.0 × 10⁵ C Thus, the total positive charge present in the copper piece is 4.0 × 10⁵ C. This follows directly from the principle of electrical neutrality, which states that the number of positive charges equals the number of electrons in a neutral body. Therefore, Option D is the correct answer.

NCERT emphasizes that many forces observed in everyday life ultimately originate from electrical interactions between atoms and molecules. Surface tension arises from intermolecular electrical forces. The forces holding atoms together in solids are also electrical in origin. However, the macroscopic gravitational force is not discussed as an electrical force in this context. Therefore, the matching represented in Option A correctly associates each force with its underlying origin. Understanding this helps explain how electrical forces contribute significantly to the structure and behavior of matter.

A body is said to be charged when it possesses either an excess or a deficiency of electrons. Excess electrons result in negative charge, while a deficit of electrons results in positive charge. Therefore, Statements 2 and 3 are correct. The total number of protons does not determine whether a body is charged because protons remain fixed within nuclei. Similarly, the total number of bound and free electrons does not define charging; only an imbalance matters. Hence, Option B correctly identifies the meaning of a charged body.

When a glass rod is rubbed with silk, some loosely bound electrons are transferred from the glass rod to the silk. As a result, the glass rod loses electrons and becomes positively charged, while the silk gains electrons and becomes negatively charged. No protons move during this process, and friction does not create new charges. The charging process simply transfers existing electrons from one body to another. Therefore, Option C accurately describes the mechanism of positive ionization by loss of electrons.