Correct: C. Gravity

Gravity is the fundamental force of attraction that exists between any two masses, any two bodies, any two particles. On Earth, gravity is what gives weight to physical objects and causes them to fall toward the ground when dropped. It is also the force that keeps the planets in orbit around the Sun and the Moon in orbit around the Earth.

Correct: B. 100

The boiling point of water is 100C 212F at standard atmospheric pressure at sea level. Boiling occurs when the vapor pressure of the liquid equals the external pressure surrounding the liquid. Because atmospheric pressure decreases as you go higher, the boiling point of water also drops at higher altitudes.

Correct: A. Nucleus

The nucleus is the small, dense region at the center of an atom, consisting of protons (which have a positive charge) and neutrons (which have no charge). Almost all of the mass of an atom is concentrated in the nucleus, even though the nucleus itself takes up only a tiny fraction of the atom's total volume.

Correct: A. Newton

The Newton (symbol N) is the SI unit of force. It is defined as the amount of force needed to accelerate a one-kilogram mass at a rate of one meter per second squared 1 m/s. It was named after Sir Isaac Newton in recognition of his work on classical mechanics, particularly his second law of motion F=ma.

Correct: C. Sun

The Sun is the ultimate source of almost all energy on Earth. Solar energy drives the weather, the ocean currents, and the seasons. Most importantly, it provides the light that plants use for photosynthesis, which creates the chemical energy (food) that sustains the entire food chain, including humans. Even fossil fuels like coal and oil are just "buried" solar energy from plants that lived millions of years ago.

Correct: A. Newton

The Newton (N) is the SI unit of force, named after Sir Isaac Newton in recognition of his laws of motion. One Newton is defined as the amount of force required to accelerate a mass of one kilogram at a rate of one meter per second squared 1 N = 1 kgm/s. It is used to measure everything from the weight of an object to the thrust of a rocket.

Correct: A. Potential

Elastic Potential Energy is the energy stored in an object when it is temporarily deformed, such as when a spring is compressed or stretched. When the spring is released, this stored energy is converted back into kinetic energy (motion). The amount of energy stored depends on the spring's stiffness and how far it has been displaced.

Correct: B. Electron

The Electron is the subatomic particle that carries a negative electrical charge. Discovered by J.J. Thomson in 1897, electrons are much smaller than protons or neutrons and orbit the nucleus of an atom in specific regions called shells. The movement of these electrons is what creates an electric current.

Correct: D. Sound

Mechanical waves, such as sound waves or water waves, require a medium (solid, liquid, or gas) to travel through. They work by causing the particles in the medium to vibrate and pass energy to their neighbors. This is why sound cannot travel through the vacuum of space-there are no particles to carry the vibrations.

Correct: D. Hertz

The Hertz (Hz) is the SI unit of frequency, named after the German physicist Heinrich Hertz. It measures the number of cycles or repetitions of a periodic event per second. For example, if a heart beats 60 times in one minute, its frequency is 1 Hz. It is commonly used to measure sound waves, radio waves, and computer processor speeds.

Correct: C. Ohm

The Ohm Omega is the primary unit of electric resistance, named after the German physicist Georg Simon Ohm. Resistance is a measure of how much a material opposes the flow of electric current. According to Ohm's Law, one Ohm is the resistance that allows one Ampere of current to flow when one Volt of potential difference is applied.

Correct: D. Series

A series circuit has only one path for the electric current to flow. This means that the same current passes through every component in the circuit. If one component fails or the path is broken, the entire circuit stops working.

Correct: A. Joule

The Joule (J) is the SI unit of work and energy. Work is done when a force is applied to an object and moves it over a distance W = F d. One Joule is equal to the work done by a force of one Newton moving an object one meter.

Correct: C. Neutron

The neutron is the subatomic particle that has no electrical charge (it is neutral). Neutrons are located in the nucleus of an atom alongside protons and have slightly more mass than a proton. They play a vital role in stabilizing the nucleus.

Correct: D. The Sun

The Sun is the primary source of energy for almost all life on Earth. It drives the weather, ocean currents, and the process of photosynthesis, which forms the base of the food chain.

Correct: C. 100

The boiling point of water is 100 degrees Celsius 100C at standard sea-level atmospheric pressure. This value is used as a fundamental reference point in the metric system of temperature. However, as altitude increases and atmospheric pressure drops, the temperature required to boil water also decreases.

Correct: B. 9.8 m/s

This value represents the average acceleration an object experiences in free fall near the Earth's surface, assuming no air resistance. While it varies slightly depending on latitude and altitude due to the Earth's rotation and shape, 9.80665 m/s is the internationally accepted standard. Understanding this constant is fundamental for calculating weight, projectile motion, and potential energy.

Correct: C. Electron

The electron is a fundamental particle that orbits the nucleus of an atom in specific energy levels or 'shells.' It has a mass roughly 1/1836th that of a proton, making it essentially negligible in most atomic mass calculations. Electrons are responsible for chemical bonding and the flow of electricity in conductive materials.

Correct: C. Refraction

Refraction is caused by the change in the speed of light as it enters a medium with a different optical density. This bending is what makes a straw look broken when placed in a glass of water and allows lenses to focus light. The degree of bending is determined by the refractive index of the materials involved, described by Snell's Law.

Correct: C. Albert Einstein

Einstein's 1905 paper on the photoelectric effect proposed that light consists of discrete packets of energy called 'quanta' or photons. This discovery provided the first experimental evidence for quantum mechanics by showing that the energy of ejected electrons depends on the frequency of light, not its intensity. Although he is more famous for E=mc, the Nobel committee felt the photoelectric effect was a more 'proven' contribution at the time.

Correct: B. Ohm's Law

Ohm's Law is expressed by the formula V=IR, where V is voltage, I is current, and R is resistance. It is the most fundamental equation for understanding and designing electrical circuits, from simple flashlights to complex computers. The law applies to 'ohmic' materials where resistance remains constant regardless of the voltage applied.

Correct: C. Tesla

The Tesla (T) is the SI unit used to quantify the intensity of a magnetic field. One Tesla is equal to one Weber per square meter, representing a very strong magnetic field; for reference, the Earth's magnetic field is about 0.00005 Tesla. It was named in honor of Nikola Tesla for his groundbreaking work in alternating current and electromagnetism.

Correct: A. First Law

The First Law of Motion states that an object at rest stays at rest, and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force. This tendency of objects to resist changes in their state of motion is known as inertia. This principle was revolutionary because it contradicted the Aristotelian view that objects naturally tend to stop.

Correct: B. Doppler Effect

The Doppler Effect is most commonly experienced when an ambulance passes you; the siren sounds higher-pitched as it approaches and lower-pitched as it moves away. In astronomy, this effect causes 'redshift' and 'blueshift,' allowing scientists to determine if stars and galaxies are moving toward or away from Earth. It is also the technology behind police radar guns and medical ultrasounds.

Correct: C. Violet

Violet light has a wavelength of approximately 380 to 450 nanometers and carries the highest energy of all colors in the visible spectrum. Beyond violet lies ultraviolet radiation, which has even higher energy and can cause damage to biological tissues. The human eye perceives these different wavelengths as distinct colors thanks to specialized cone cells in the retina.

Correct: C. Conservation of Angular Momentum

Conservation of Angular Momentum states that the total angular momentum of a system remains constant unless acted upon by an external torque. By pulling their arms in, the skater reduces their 'moment of inertia,' and because the total momentum must stay the same, their rotational speed must increase. This same principle governs the formation of galaxies and the rapid spin of neutron stars.

Correct: B. Focus (or Focal Point)

The focal point is where parallel rays of light meet after being refracted by a convex lens or reflected by a concave mirror. The distance from the center of the lens to this point is known as the focal length, which determines the lens's magnifying power. Cameras and eyes adjust this focus to create sharp images on the sensor or retina.

Correct: B. Watt

The Watt (W) measures the rate of energy transfer or work being done. It is used to quantify the consumption of electricity in lightbulbs, the output of engines, and the power of solar radiation hitting the Earth. The unit is named after James Watt, whose improvements to the steam engine were central to the Industrial Revolution.

Correct: C. Photon

A photon is an elementary particle that has zero rest mass and travels at the speed of light in a vacuum. It exhibits both wave-like and particle-like properties, a core concept known as wave-particle duality. Photons are the 'force carriers' for the electromagnetic force, meaning they transmit the interaction between charged particles.

Correct: C. Infrared

Infrared (IR) radiation is emitted by all objects as a result of their thermal energy, which is why IR cameras can 'see' heat signatures in total darkness. It is divided into near, mid, and far infrared, with various applications ranging from television remote controls to deep-space astronomy. The James Webb Space Telescope primarily observes in infrared to see through cosmic dust.

Correct: C. Orbitals

Unlike the fixed 'orbits' of planets, electrons in an atom exist in cloud-like orbitals that represent a statistical probability of their location. These orbitals have different shapes, such as the spherical 's' orbital or the dumbbell-shaped 'p' orbital, based on their energy levels. Quantum mechanics dictates that we can never know the exact path of an electron, only the shape of its orbital.

Correct: A. 299,792,458 m/s

The speed of light, denoted as 'c,' is a universal constant that plays a fundamental role in nearly all branches of physics, including relativity and electromagnetism. According to Einstein's theories, any object with mass would require infinite energy to reach this speed, meaning only massless particles like photons can travel at c. It is used as the basis for defining the length of a meter.

Correct: B. Dark Matter

Dark matter was first proposed to explain why galaxies rotate much faster than the visible matter within them would allow. While we cannot see it directly, its presence is inferred by its gravitational effects on stars, galaxies, and the bending of light (gravitational lensing). Scientists are currently searching for 'WIMPs' (Weakly Interacting Massive Particles) as the most likely candidate for what dark matter is made of.

Correct: C. Red

Red light has a wavelength of approximately 620 to 750 nanometers and carries the least energy of any color in the visible spectrum. Because it has a long wavelength, red light is scattered less by the atmosphere, which is why it is used for stoplights and why sunrises and sunsets appear red. Beyond red lies infrared radiation, which we feel as heat.

Correct: B. Law of Conservation of Energy

The Law of Conservation of Energy (the First Law of Thermodynamics) states that energy cannot be created or destroyed, only transformed from one form to another. For example, a falling ball converts potential energy into kinetic energy, and then into heat and sound upon hitting the ground. This principle is a cornerstone of classical and modern physics, used to solve problems in every field from mechanics to cosmology.

Correct: C. The maximum displacement of the wave from its equilibrium position

Amplitude relates to the 'intensity' or 'strength' of a wave; for sound waves, a higher amplitude means a louder sound, and for light waves, it means a brighter light. It is measured from the center line of the wave to the top of a crest or the bottom of a trough. The energy carried by a wave is generally proportional to the square of its amplitude.

Correct: B. Newton's Law of Universal Gravitation

Newton's Law of Universal Gravitation explained for the first time why planets orbit the sun and why objects fall to the ground on Earth. It follows an 'inverse-square law,' meaning that if you double the distance between two objects, the gravitational pull between them drops to one-fourth. While Einstein's General Relativity later provided a more accurate description for extreme cases, Newton's law is still used for almost all space missions today.

Correct: C. Sublimation

Sublimation occurs when the molecules of a solid gain enough energy to overcome atmospheric pressure and transition directly to a vapor. The most common example is 'dry ice' (solid carbon dioxide), which disappears into a fog of CO2 gas at room temperature. It is also the process used in freeze-drying food to preserve its texture and nutrients.

Correct: B. Centripetal Force

Centripetal force is not a 'new' type of force but a role filled by other forces, such as gravity for a planet or tension for a ball on a string. Without this inward pull, the object would fly off in a straight line due to inertia. The 'centrifugal force' that people feel pushing them outward is actually just their own inertia resisting the turn.

Correct: B. Terminal Velocity

Terminal velocity is reached when the downward force of gravity is exactly balanced by the upward force of air resistance (drag). At this point, the object stops accelerating and continues to fall at a constant speed. For a human skydiver in a standard 'belly-to-earth' position, terminal velocity is about 120 mph (193 km/h).

Correct: C. Mole

The mole (mol) allows scientists to connect the subatomic world of atoms and molecules to the macroscopic world of grams and liters. The number of entities in a mole is known as Avogadro's Number, which was recently redefined to be an exact mathematical constant. It is fundamental for chemical reactions and gas laws in physics.

Correct: C. Conductivity

Electrical conductivity () is a measure of how easily electrons can flow through a material when a voltage is applied. Metals like silver, copper, and gold have high conductivity because they have many 'free' electrons, while insulators like rubber and glass have extremely low conductivity. Conductivity is the mathematical inverse of resistivity.

Correct: B. The fluid's resistance to flow or deformation

Viscosity is often thought of as the 'thickness' of a fluid; for example, honey has a high viscosity while water has a low one. It is caused by internal friction between the molecules as they slide past each other. Viscosity is highly dependent on temperature, usually decreasing for liquids as they get warmer.

Correct: C. Kinetic Energy

Kinetic energy is calculated using the formula 1/2 mv, where m is mass and v is velocity. Because the velocity is squared, an object's kinetic energy increases four times whenever its speed doubles, which is why high-speed car crashes are so much more destructive. When an object stops, its kinetic energy must be converted into another form, such as heat in the brakes.

Correct: C. Mass

In Albert Einstein's mass-energy equivalence formula, 'm' represents the mass of an object, while 'c' represents the speed of light in a vacuum. The equation shows that energy and mass are interchangeable and that a small amount of mass can be converted into a massive amount of energy. This discovery provided the theoretical basis for both nuclear power and the development of atomic weapons.