General Science: 80+ Most Important Science Laws & Principles

Question 1. Describe Boyle’s law in words (not with an equation).
Boyle’s law: If the temperature of a fixed amount of gas is constant, the volume and pressure are inversely proportional.

Question 2. Describe Charles’s law in words (not with an equation).
Charles’s law: If the pressure of a fixed amount of gas is constant, the volume and temperature are directly proportional.

Question 3. Show how the ideal gas law combines Boyle’s and Charles’s laws. You may use math.
The ideal gas law is PV = nRT. If the temperature is constant and the amount of gas is fixed, PV = const., meaning that P = const. / V according Boyle’s law. If the pressure is constant and the amount of gas is fixed, V = const. × T according to Charles’s law.

Question 4. What is capillary action?
Capillary action: When a glass capillary (which is a tube with a narrow diameter) is placed in a liquid, the liquid rises up the tube until the forces of adhesion, cohesion, and gravity are balanced.

Question 5. What is the periodic law?
Periodic law: When the elements are arranged according to atomic number, some properties occur at regular (or periodic) intervals.

Question 6. What is the law of reflection?
Law of reflection: When a beam of light is incident upon a smooth surface, the reflected ray travels symmetrically, with the angle of reflection equal to the angle of incidence (where each angle is measured from the normal).

Question 7. What does it mean for energy to be conserved?
Conservation of energy: The total energy of the system and its surroundings is constant. Energy is neither created nor destroyed, but may change form.

Question 8. What form does conservation of energy take for chemical reactions?
For a chemical reaction, conservation of energy leads to conservation of mass. (Mass isn’t conserved in general, such as for nuclear reactions. An extreme example is when an electron and positron annihilate, producing photons with zero rest mass.)

Question 9. What are Newton’s three laws of motion? (Bonus if you know which is which.)
Newton’s first law (inertia): Objects tend to maintain constant momentum. (We’ll accept constant velocity, but constant speed isn’t as good.)
Newton’s second law: The net force on an object equals its mass times acceleration.
Newton’s third law: If A exerts a force on B, then B exerts a force on A that is equal in magnitude but opposite in direction. (There is an equal and opposite reaction to every action.)

Question 10. What are Kepler’s laws of planetary motion?
Kepler’s first law: Planets travel in elliptical orbits with the sun at one focus.
Kepler’s second law: Planets sweep out equal areas in equal times.
Kepler’s third law: The square of a planet’s orbital period is proportional to the cube of the semimajor axis of its (elliptical) orbit.

Question 11. What are the three laws of thermodynamics? (Bonus if you know the zeroth law, too.)
First law of thermodynamics: The change in internal energy of a system (with constant mole numbers) equals the heat absorbed minus the work done.
Second law of thermodynamics: The total entropy of a system plus its surroundings can’t decrease. Alternatively, a heat engine can’t be perfectly efficient.
Third law of thermodynamics: It is impossible to reach exactly absolute zero.
Zeroth law of thermodynamics: If A and B are each in thermal equilibrium with C, then A and B are also in thermal equilibrium with each other.

Question 12. What is the law of definite proportions?
Law of definite proportions: The ratio of the elements is always the same for a given pure compound. (The compound has a constant composition.)

Question 13. What is Occam’s razor?
Occam’s razor: The simplest explanation (requiring the fewest assumptions) is generally preferable. (This is technically a principle of philosophy.)

Question 14. What are Mendel’s laws (or principles)?
Mendel’s law of dominance: Alleles may be dominant or recessive. If there is at least one dominant allele, this allele gets used.
Mendel’s law of segregation: The alleles for each gene segregate when a gamete forms.
Mendel’s law of independent assortment: The segregation of alleles for one gene can be independent of the segregation of alleles for other genes.

Question 15. What is Pascal’s law?
Pascal’s law: If the pressure applied to an enclosed liquid changes, that change in pressure is transmitted throughout the liquid (undiminished). This is why we add the atmospheric pressure, P0, to to find the pressure in a fluid.

Question 16. What is the pressure-flow hypothesis?
Pressure-flow hypothesis: Sap is transported in the phloem of plants from sources of sugar (like leaves) to regions with less sugar via pressure flow.

Question 17. What is Avogadro’s law?
Avogadro’s law: If gases with equal volumes have the same pressure and the same temperature, they will contain the same number of molecules.

Question 18. What is Dalton’s law of partial pressures?
Dalton’s law of partial pressures: For a mixture of (non-reacting) gases, the total pressure of the mixture equals the sum of the pressures (called partial pressures) that each gas would exert (if it were the only gas).

Question 19. Describe Newton’s law of gravity in words (not with an equation).
Newton’s law of gravity: Two masses attract one another with a gravitational force that is directly proportional to each mass and inversely proportional to the square of the separation between their centers.

Question 20. Describe Coulomb’s law in words (not with an equation).
Coulomb’s law: Two charges attract or repel one another with an electric force that is directly proportional to each charge and inversely proportional to the square of the separation between their centers. The force is attractive for opposite charges and is repulsive for like charges.

Question 21. What is the right-hand rule of magnetism? (Bonus if you know two.)
One right-hand rule of magnetism relates current, magnetic field, and magnetic force. There is more than one equivalent way to formulate this right-hand rule. One way is to point the extended fingers of your right hand along the current, twist your forearm while still pointing the fingers along the current until you can naturally bend your fingers toward the magnetic field, and then your extended thumb will point along the magnetic force. We’ll accept a (correctly) labeled diagram.
A second right-hand rule helps to determine the magnetic field lines created by a current. Wrap the fingers of your right hand along the wire with your thumb along the current. The curled fingers represent magnetic field “lines” circulating around the current (the fingernails indicate which way).

Question 22. Describe Ohm’s law in words (not with an equation).
Ohm’s law states that for a given conductor (which has a particular resistance), the potential difference across the conductor is proportional to the current.

Question 23. What are Kirchhoff’s rules? Briefly describe each.
Kirchhoff’s junction rule states that the sum of the currents entering a junction equals the sum of the currents exiting the junction.
Kirchhoff’s loop rule states that the voltage drops and rises sum to zero going around any closed loop (following a set of sign conventions adopted in a physics text).

Question 24. Describe Hooke’s law in words (not with an equation).
Hooke’s law states that a spring will exert a restoring force, tending toward the equilibrium position, which is proportional to its displacement from equilibrium.

Question 25. Describe Snell’s law in words (not with an equation).
Snell’s law states that a ray of light will refract towards the normal if it passes into a medium with a higher index of refraction or away from the normal if it passes into a medium with a lower index of refraction. (The equation for Snell’s law predicts the precise angle of refraction.)

Question 26. What is the competitive exclusion principle?
Competitive exclusion principle: If two species compete for the same (limited) resource, they can’t both coexist with constant population values. One species will have an advantage, dominating in the long term. The other may become extinct or adapt to a new niche, for example.

Question 27. What is the Pauli exclusion principle?
Pauli exclusion principle: Two electrons in the same atom can’t have the same set of quantum numbers.

Question 28. What is the octet rule?
Octet rule: Elements tend to gain, lose, or share electrons in chemical bonding in such a way as to have eight valence electrons. (Although this general rule is very useful, it has exceptions, such as ionic bonds with transition metals.)

Question 29. Describe the Doppler effect in words (not with an equation).
Doppler effect: When there is relative motion between the source of a wave (such as a sound wave) and an observer, the frequency of the waves as measured by the observer will be different from the frequency of the waves as produced by the source. If the source and observer are getting farther apart, the measured frequency will be lower, and if they are getting closer together, the measured frequency will be higher.

Question 30. What is genetic drift?
Genetic drift refers to a change in the frequency of alleles (in a relatively small gene pool) that occurs by chance (such as by the bottleneck or founder effects).

Question 31. What is plate tectonics?
Plate tectonics is the theory that rigid plates in earth’s lithosphere slowly move and interact, producing mountains, volcanoes, earthquakes, etc.

Question 32. What is continental drift?
Continental drift is the hypothesis that the continents were originally part of a supercontinent (the Pangaea) and have slowly drifted apart.

Question 33. Describe Heisenberg’s uncertainty principle in words (not with an equation).
Heisenberg’s uncertainty principle: The more precisely the position of a particle is measured, the more uncertainty there is in the particle’s momentum, and vice-versa. (It’s impossible to know its exact position and momentum simultaneously.)

Question 34. Describe Archimedes’ principle in words (not with an equation).
Archimedes’ principle: When an object is submerged in a fluid, the magnitude of the buoyant force equals the weight of the displaced fluid.

Question 35. What is Olbers’s paradox?
Olbers’s paradox: If the stars (or galaxies) are distributed uniformly throughout space, light should be reaching earth from every direction such that the sky should appear uniformly bright. However, the sky isn’t uniformly bright at night. (Possible explanations include redshift and the expansion and limited age of the universe.)

Question 36. What is conservation of momentum? For which kinds of problems is it really useful?
Conservation of momentum: When the net external force acting on a system is zero, the total momentum of the system remains constant. It is particularly useful to apply this concept to problems that involve collisions or scattering.

Question 37. What is conservation of angular momentum?
Conservation of angular momentum: When the net external torque acting on a system is zero, the total angular momentum of the system remains constant.

Question 38. Describe the parallel-axis theorem in words (not with an equation).
Parallel-axis theorem: If the moment of inertia about an axis passing through the center of a rigid body is known, the moment of inertia about another axis that is parallel to the axis through the center can be found by adding the mass of the rigid body times the square of the distance between these axes.

Question 39. What is the theory of acquired characteristics?
The theory of acquired characteristics is the notion that organisms could acquire traits during their lifetime and pass them on to offspring. (Textbooks label this idea as Lamarckian, though it may not paint a complete picture of Lamarck’s theory of evolution, and present this theory in order to offer contrast with Darwin’s theory.)

Question 40. What is gravitational redshift?
Gravitational redshift: An increase in the wavelength of a photon that occurs as the photon travels from a higher gravitational field to a lower gravitational field. (Gravitational redshift is different from the Doppler redshift that causes the spectrum of a star to shift as a result of the star moving away from the earth.)

Question 41. Describe the de Broglie relation in words (not with an equation).
The de Broglie relation explains that a particle like an electron exhibits wave-like properties, such that the wavelength is inversely proportional to its momentum.

Question 42. What is the principle of superposition in geology?
Principle of superposition (in geology): The layers of strata in an undeformed sequence are ordered by age (youngest at the top, oldest at the bottom).

Question 43. What is the cosmological principle?
Cosmological principle: The distribution of matter in the universe (on a vast scale) should be homogeneous (uniform) and isotropic (the same in all directions).

Question 44. Describe Gauss’s law of electrostatics in words (not with an equation).
Gauss’s law: The net flux of electric field lines passing through a closed surface (even an imaginary one) is proportional to the net charge enclosed by the surface.

Question 45. Describe Ampère’s law in words (not with an equation).
Ampère’s law: The net circulation of magnetic field lines around a closed curve (even an imaginary one) is proportional to the net current passing through the area bounded by the closed curve (by “circulation,” we mean the line integral).

Question 46. What is Fermat’s principle?
Fermat’s principle: Light tends to follow the path of least time.

Question 47. Describe Faraday’s law in words (not with an equation).
Faraday’s law: A current is induced in a loop of wire when the net magnetic flux passing through the loop changes in time. It is critical to say that it “changes,” and for maximum credit you should say “flux” (not “field”). You may discuss inducing an emf rather than a current.

Question 48. What is Lenz’s law?
Lenz’s law: The direction of the current in Faraday’s law is such that it tends to oppose the changing magnetic flux. You may discuss an emf rather than a current.

Question 49. What is the endosymbiotic theory?
Endosymbiotic theory: eukaryotic cells evolved from a symbiotic relationship among a variety of prokaryotes.

Question 50. What is Galilean relativity?
Galilean relativity: When an object and observers have relative velocities that are very small compared to the speed of light, the velocity of the object to each observer can be found from simple vector subtraction.

Question 51. What is Einstein’s special theory of relativity?
Einstein’s special theory of relativity describes coordinate transformations between observers and objects when the relative velocities are constant, even when the speeds are comparable to the speed of light.

Question 52. What is Einstein’s general theory of relativity?
Einstein’s general theory of relativity describes coordinate transformations between observers and objects when there is acceleration, including acceleration that is created by the gravitational attraction of massive bodies.

Question 53. Describe Graham’s law of effusion in words (not with an equation).
Graham’s law of effusion: The rate of effusion of a gas is inversely proportional to the square root of its molar mass.

Question 54. What is Markovnikov’s rule?
Markovnikov’s rule: When a protic acid HX adds to an asymmetric alkene (or alkyne), the H of HX bonds to the carbon atom that had the most H atoms.

Question 55. What are the Stark effect and the Zeeman effect?
The Stark effect refers to the splitting of spectral lines in the presence of an electric field, while the Zeeman effect refers to splitting in the presence of a magnetic field.

Question 56. What is Brewster’s law?
Brewster’s law: When unpolarized light is incident upon a surface, the reflected ray is completely polarized if the reflected ray is perpendicular to the refracted ray.

Question 57. Describe Malus’s law in words (not with an equation).
Malus’s law: When polarized light passes through a polarizer, the intensity of light passing through the polarizer is reduced by a factor equal to the square of the cosine of the angle between the original polarization and the axis of the polarizer.

Question 58. Describe Torricelli’s law in words (not with an equation).
Torricelli’s law: If a small hole is made in a container of liquid (that is open at the top), the speed of efflux through the hole is the same as if an object had been in free fall from rest along a height equal to the depth of the hole from the top surface.

Question 59. Describe Bernoulli’s principle in words (not with an equation).
Bernoulli’s principle expresses conservation of energy to an ideal fluid for two points along a streamline: The sum of the pressure, kinetic energy per unit volume, and gravitational potential energy per unit volume is constant along the streamline.

Question 60. What is the principle of faunal succession?
Principle of faunal succession: The fossils found in the strata of sedimentary rock succeed one another in a definite, determinable order.

Question 61. What is the photoelectric effect?
Photoelectric effect: When light with sufficient frequency is incident upon a metal, electrons are ejected from the surface.

Question 62. What is the Compton effect?
Compton effect: When a photon scatters off of an electron that is initially at rest, the wavelength of the photon increases as a result of the interaction (except in the case of a grazing collision where the scattering angle is exactly zero).

Question 63. Describe Henry’s in words (not with an equation).
Henry’s law: The solubility of a gas in a solvent is directly proportional to the partial pressure of the gas over the solution.

Question 64. What is Hess’s law?
Hess’s law: The enthalpy change for a multi-step reaction equals the sum of the enthalpy changes for the individual steps of the reaction. (Enthalpy is an extensive parameter; it is a state function.)

Question 65. What is Hubble’s law?
Hubble’s law: The redshift in the spectra of a distant galaxy is proportional to its distance from earth. You may describe the speed of recession instead of redshift.

Question 66. What is Hund’s rule?
Hund’s rule: For degenerate orbitals (meaning that they have the same energy), one electron is placed in each orbital before electrons are paired. Unpaired electrons have the same spin.

Question 67. What is the Chandrasekhar limit?
The Chandrasekhar limit: The maximum mass of a star (approximately equal to 1.4 solar masses) for which a white dwarf can exist (otherwise, the star would not be able to support electron degeneracy).

Question 68. What is the Roche limit?
The Roche limit: If an object (or blob of gas) is held together only by the gravitational attraction of its parts, the object can’t be too close to a planet (star, moon, etc.) or it will break apart. This critical distance is known as the Roche limit. (Even a rigid satellite has a minimum distance in order not to break apart from tidal forces.)

Question 69. What is Bragg’s law? (We’ll accept an equation for this answer.)
Bragg’s law: The condition for constructive interference for the diffraction of an x-ray by a crystal consisting of parallel planes of atoms is
(where m is a positive integer and d is the spacing between adjacent planes).

Question 70. What is the law of DuLong and Petit?
Law of DuLong and Petit: At sufficiently high temperatures (above about 300 K), the molar specific heat (at constant volume) of a solid is approximately equal to three times the universal gas constant.

Question 71. What is Le Châtelier’s principle?
Le Châtelier’s principle: If a system in equilibrium is disturbed by a spontaneous inhomogeneity or fluctuation in temperature, pressure, or the concentration of a component, the system will tend to return to its original equilibrium condition (provided that the system isn’t undergoing a macroscopic change that would affect the equilibrium conditions, such as a piston suddenly made movable).

Question 72. What is Huygens’ principle?
Huygens’ principle: Each point on a wavefront serves as a point source for a new set of spherical waves.

Question 73. Describe Wien’s law in words (not with an equation).
Wien’s law: The wavelength which maximizes the spectral radiance (or emittance) of blackbody radiation is inversely proportional to the absolute temperature. Note: It would be incorrect to call it the “maximum wavelength” even though texts call it
The maximum wavelength is infinite. What means is the “wavelength for which the spectral radiance is a maximum.”

Question 74. Describe Stefan’s law in words (not with an equation).
Stefan’s law: The intensity (or power per unit area) radiated by a black body is proportional to the fourth power of the absolute temperature. Notes: You may call it the radiance (but not spectral radiance) or emittance instead of intensity. Note that we write “blackbody” together as an adjective but “black body” separate as a noun.

Question 75. What is the Meissner effect?
Meissner effect: All magnetic fields are expelled from the interior of a superconductor below the critical temperature.

Question 76. What is Curie’s law?
Curie’s law: The magnetization of a paramagnetic material is directly proportional to the applied magnetic field and inversely proportional to the absolute temperature (for sufficiently high temperatures and low magnetic fields). If you wrote this as an equation, we’ll accept it for this answer (the question didn’t specify not to).

Question 77. What is Raoult’s law?
Raoult’s law: The partial pressure of a solvent vapor above a solution is equal to the vapor pressure of the pure solvent times the mole fraction of the solvent in the solution. We’ll also accept this in equation form for this answer.

Question 78. What is the Weber-Fechner law?
Weber-Fechner law: In order for two stimuli to be perceived as different, they must differ by some minimum percentage (as opposed to differing by some minimum amount). That is, the minimum difference is proportional to the stimulus.

Question 79. Describe the Hardy-Weinberg principle in words (not with an equation).
Hardy-Weinberg principle: The frequencies of alleles in a population tend to remain constant (unless factors are present to cause the frequencies to change).

Question 80. Describe what Price’s theorem does (in the context of biology).
Price’s theorem provides a mathematical formulation of evolution and natural selection.

Question 81. Describe the Hall effect in words (not with an equation).
Hall effect: When a current-carrying conductor is in the presence of a magnetic field, a voltage is produced which is perpendicular to the magnetic field and is also perpendicular to the current.

Question 82. What is the law of constancy of interfacial angles?
Law of constancy of interfacial angles: For a given crystal (such as a mineral), the angles between corresponding faces are the same (for the same temperature), except for the case of polymorphism.

Question 83. What is the principle of least action?
Principle of least action: If a system with fixed energy begins in one state and finishes in another state, the path taken is the one that minimizes the action (which is the integral of the Lagrangian over time). Instead of “minimize,” you might refer to “stationary.” (This principle is applied to derive equations of motion.)