Basic Physics Practice Questions!

Air is the worst conductor among the given substances. This is because air is a poor conductor of heat and electricity due to its low density and lack of free electrons. Unlike copper and iron, which are metals and have a high number of free electrons that can easily carry heat or electricity, air molecules are widely spaced and do not have many free electrons available for conduction. Similarly, salt water contains ions that can conduct electricity, making it a better conductor than air.

The correct answer is "there must always be two or more elements." This is because a compound is formed when two or more different elements chemically combine in a fixed ratio. A single atom of an element does not constitute a compound as it lacks the presence of multiple elements. The other options, such as atoms being mixed but not joined or a shortage of electrons, do not define compounds but rather describe other concepts like mixtures or electron deficiencies.

According to Ohm's Law, the current (I) flowing through a circuit is equal to the voltage (V) across the circuit divided by the resistance (R) of the circuit. In this case, the voltage is given as 1 volt and the resistance is given as 2 ohms. Therefore, the current is calculated as 1 volt divided by 2 ohms, which equals 0.5 amperes or half an ampere.

If a material has low resistance, it means that it allows the flow of electric current with ease. A good conductor is characterized by low resistance, as it allows the free movement of electrons. Therefore, the statement "it is a good conductor" is the correct answer.

A stroke of lightning is a discharge of static electricity. This occurs when there is a buildup of electrical charge in the atmosphere, typically between a cloud and the ground or between two clouds. When the electrical potential difference becomes high enough, it causes a rapid and visible discharge of electricity in the form of lightning. This discharge is often accompanied by a bright flash of light and a loud thunderclap. The movement of holes in an insulator, having a low current, or being caused by a buildup between clouds are not accurate explanations for a stroke of lightning.

Copper is the best conductor among the given substances. Copper has a high electrical conductivity due to its atomic structure. It has free electrons that can easily move through the material, allowing for efficient flow of electric current. This makes copper widely used in electrical wiring and other applications where good conductivity is required. Air, iron, and salt water have lower conductivity compared to copper, making copper the best choice among the given options.

A photovoltaic cell, also known as a solar cell, converts visible light into electricity through the photovoltaic effect. This process involves the absorption of photons from sunlight, which excites electrons in the cell's semiconductor material, creating an electric current. Unlike dry cells and wet cells, which are used to produce electric current through chemical reactions, and incandescent bulbs, which convert electricity into light, a photovoltaic cell directly converts light energy into electrical energy. Therefore, the correct answer is in a photovoltaic cell.

When a battery is charged, electrical energy is converted into chemical energy, allowing the battery to store energy for later use. This process involves reversing the chemical reactions that occur during discharging, restoring the battery's capacity to provide electrical power. Therefore, charging a battery replenishes its chemical energy and allows it to be reused.

The volt is the standard unit of electromotive force. Electromotive force refers to the energy per unit charge that is provided by a source, such as a battery, to move electric charges in a circuit. It is commonly symbolized by the letter "V". The volt is used to measure the potential difference or voltage across a circuit component, indicating the amount of energy that can be transferred to the charges as they move through the circuit.

An electric generator is the best description for a backward-working electric motor that converts mechanical rotation into electricity. This is because a generator is a device that converts mechanical energy into electrical energy. It operates by using a magnetic field to induce an electric current in a conductor, thereby generating electricity.

The atomic weight of an element is determined by the combined mass of its protons and neutrons in the nucleus. The number of protons gives the atomic number, which identifies the element, while the number of neutrons contributes to the atomic mass. Therefore, the atomic weight is approximately determined by the number of neutrons plus the number of protons.

An ion is an atom or molecule that has gained or lost one or more electrons, resulting in a positive or negative charge. This means that ions can have either a positive or negative charge, depending on whether they have gained or lost electrons. Therefore, the correct answer is that an ion can have either a positive or negative charge.

When an electrical insulator is ionized, it means that it is being transformed into a material that can conduct electricity. Ionization occurs when atoms or molecules gain or lose electrons, resulting in the formation of charged particles called ions. This process creates a pathway for the flow of electric current through the previously insulating material. Heating, cooling, and oxidizing an insulator do not have the same effect of enabling conductivity.

When a fluctuating magnetic field is present, it induces an electric field in the surrounding space. This induced electric field is also fluctuating in nature. This phenomenon is known as electromagnetic induction and is described by Faraday's law of electromagnetic induction. According to this law, a changing magnetic field induces an electric field, which in turn can produce an electric current. Therefore, the correct answer is that a fluctuating magnetic field produces a fluctuating electric field.

When two neutrons are added to the nucleus of an oxygen atom, the atomic weight increases. The atomic weight is determined by the sum of the protons and neutrons in the nucleus. Since the nucleus originally contained eight protons and eight neutrons, the atomic weight was 16. By adding two more neutrons, the resulting atomic weight becomes 18.

The atomic number of an element is determined by the number of protons. The atomic number represents the number of protons in the nucleus of an atom. It is a unique identifier for each element and determines its position on the periodic table. The number of neutrons can vary in different isotopes of the same element, but the number of protons remains constant. The number of electrons can also vary, but it is equal to the number of protons in a neutral atom. Therefore, the correct answer is the number of protons.

Isotopes are atoms that have the same number of protons but different numbers of neutrons. While the number of protons determines the element's identity, the number of neutrons can vary, resulting in different isotopes. The charge of an atom depends on the balance between the number of protons and electrons. Since isotopes have the same number of protons, they can have different numbers of electrons, leading to a positive or negative charge. Therefore, isotopes can have either a positive or negative charge.

A molecule can consist of a single atom of an element because some elements, such as hydrogen or oxygen, can exist as individual atoms and do not need to bond with other atoms to be stable. These single-atom molecules are called diatomic molecules.

When holes move in a semiconductor, it means that electrons are moving from one atom to another, leaving behind a positively charged "hole" in the atom. This movement of holes results in the flow of electric current. The movement of holes is similar to the flow of electrons, as both involve the movement of charged particles. However, it is important to note that the movement of holes does not require a high current; it can occur even with a low current. Therefore, the correct answer is that the movement of holes in a semiconductor results in a certain amount of electric current.

The correct answer is "is an extremely large number of charge carriers." A coulomb is a unit of electric charge, and it represents a large quantity of charge carriers. One coulomb is equal to the charge of approximately 6.242 × 10^18 electrons or other elementary charged particles. Therefore, it can be said that a coulomb represents an extremely large number of charge carriers.