Understanding Physics can be simpler with a thorough knowledge of the various important laws of Physics. The list of all laws, principles, and theorems in Physics is long. The following article is a compilation of the different crucial laws of Physics that enunciate several branches of the subject, showing their importance in the field of scientific study. Students preparing for NEET 2022 or JEE 2022 must get well-versed with each of these laws to ace their upcoming exams. Often numerical problems and reasoning questions are based on the fundamental laws of Physics.
34 Important Laws of Physics
The following physical laws are conclusions drawn from years of scientific observations by great Physicists. They performed several experiments repeatedly under varying conditions to reach inferences that are now accepted worldwide. These laws are validated and reviewed by scientific communities over time.
According to Ampere’s law, the electric current produces a magnetic field proportional to its size with the permeability of the free space as a constant of proportionality. Maxwell’s fourth equation depicts this relationship:
∇ x H = J + ∂D/∂t
When a body is completely or partially dipped in a fluid, it experiences an upward pushing force. This force is called the buoyant force and is equal to the weight of the displaced fluid by the body. When the body is completely immersed in the fluid, the volume of the fluid displaced is equal to the volume of the body immersed.
The equation describes the relationship between the magnetic field produced by a constant electric field- a current-carrying segment (a vector quantity called the current element).
B = (μ0 NI) 2R
- B is magnetic field intensity
- μ0 is the permeability of free space
- N is the number of turns
- I is current intensity
- R is radius
The law states that for a given sample, its path length and concentration are directly proportional to the absorbance of light. Beer-lambert’s equation is as follows:
I = I0 e-μ (x)
- I is the intensity of light
- I0 is the initial intensity
- μ is the coefficient of absorption
- x is the depth in metre
The law states that the volume and pressure of a gas at a constant temperature are inversely proportional to each other when the quantity of gas is kept constant. The formula is as follows:
PV = k
The relationship for light waves states that the maximum polarisation of an unpolarised light ray can be obtained by allowing the ray to fall on a surface of a transparent medium such that the refracted ray makes and the reflected ray makes an angle of 90°. Brewster’s law formula:
μ = tan i
- i is the polarisation angle
- μ is the refractive index
The X-ray incident onto a crystal surface with an angle of incidence, θ, will have the same scattering angle while reflecting, i.e., θ. So, when the path difference (d) equals a whole number, n, of wavelength, λ, constructive interference occurs. Bragg’s equation:
nλ = 2d sinθ
The attractive or repulsive force between two charged bodies is inversely proportional to the square of the distance (d) between them and directly proportional to the product of their charges (q1 and q2). The force acts along the line joining the two charges. So, F ∝ q1q2/d2.
The magnetic susceptibility χ stays above the Curie temperature point of a ferromagnet in the paramagnetic region.
The law of heat conduction or Fourier’s law states that the negative temperature gradient and heat transfer time rate is proportional to that gradient’s area at the right angles through which the heat flows. It can be stated as follows:
k = -q▽T
- q is the local heat flux density
- k is the conductivity of the material
- ▽T is the temperature gradient
According to Faraday’s first law of electromagnetic induction, an emf is induced on a conductor placed in a varying magnetic field. On closing the conductor circuit, a current will be induced. It is called induced current.
The second law of electromagnetic induction states that the induced electromotive force equals the rate of change of flux linkage.
Laws of Thermodynamics
Zeroth Law: When two thermodynamic systems are in thermal equilibrium with a third one, then the three are in thermal equilibrium with each other.
First Law of Thermodynamics: Heat is a form of energy. So, all thermodynamic processes follow the principle of energy conservation, i.e., heat cannot be created or destroyed but can be transferred and converted to other forms.
Second Law of Thermodynamics: A spontaneously occurring process always leads to an escalation in the entropy (S) of the universe.
Third Law of Thermodynamics: The entropy of a perfect crystal at absolute zero (zero Kelvin temperature) is zero.
Every point on a wavefront is a source of secondary waves or wavelets. The sum of these wavelets forms a wavefront.
The strain on the material is directly proportional to the stress applied to the material as long as it is within the elastic limit of that material.
The redshift or the galaxy’s velocity is directly proportional to its distance.
Ideal Gas Law
The product of volume (V) and pressure (P) of a gram molecule of ideal gas equals the product of absolute temperature (T) and ideal gas constant (R). The equation can be stated as follows:
PV = nRT
Inverse Square Law
The radiation intensity is inversely proportional to the square of the distance, i.e.,
I ∝ 1/d2
First law: A mathematical expression showing the relationship between heat produced by electric current flowing via a conductor. When Q is the amount of heat, I is for the electric current, R is the resistance in the conductor, and T denotes time, the relation can be written as follows:
Q = I2 RT
Kirchoff’s current law: The total current entering a node/junction equals the charge leaving the node such that no charge is lost.
Kirchoff’s voltage law: For a closed network, the voltage throughout a loop equals the sum of each voltage drop in the same loop and equals zero.
Lambert’s Cosine Law
The radiant intensity from an ideal diffusely reflecting surface is directly proportional to cos θ, the angle between the direction of incident light and surface normal. It is also called Lambert’s emission law.
Law of Conservation of Mass
The mass in an isolated system can neither be created nor destroyed. It can only be transformed into other forms.
Law of Conservation of Energy
The energy in a closed system can neither be created nor destroyed. It can only be transformed into other forms.
Law of Equipartition of Energy
The total energy for the system is equally divided among the degrees of freedom, i.e., along the x, y, and z axes, for a dynamic system in thermal equilibrium.
Laws of reflection
Whenever light falls on a smooth surface, the incident angle equals the reflected angle. The normal, incident and reflected rays lie in the same plane.
Laws of Friction
The five laws of friction are as follows:
- A moving object’s friction is proportional and perpendicular to the normal force.
- The friction depends on the nature of the surface an object is in contact with.
- Friction is independent of the area of contact while there is a contact.
- Kinetic friction doesn’t depend on velocity.
- The coefficient of kinetic friction is lesser than the coefficient of static friction.
Law of Conservation of Linear Momentum
The momentum of the system remains constant when the net external force acting on a system of bodies is zero.
The induced emf with different polarities gives rise to a current whose magnetic field opposes the magnetic flux change through the loop, ensuring that the original flux is maintained through the loop when the current flows through it.
Universal gravitation: The attractive force between any two objects in the universe is directly proportional to their masses’ product and inversely proportional to the square of the intermediary distance.
Newton’s First law of motion: A body continues to stay at rest or in motion unless acted upon by an external force. It is also called the law of inertia.
Newton’s Second law of motion: Force is equal to mass times acceleration, i.e., it is equivalent to the rate of change of momentum.
Newton’s Third law of motion: Every action has an equal reaction in the opposite direction.
Law of viscosity: The shear stress between two adjacent layers of a fluid is directly proportional to the velocity gradient.
The voltage across a conductor is directly proportional to the current flowing through it when the physical conditions and temperature remain constant.
Whenever an external pressure is applied to a confined liquid, it gets evenly distributed throughout the liquid in all possible directions.
Radioactive Decay Law
The probability of decay of a nucleus per unit of time is a constant, independent of time.
For two given media, the ratio of the sines of the angle of incidence θ1 and angle of refraction θ2 is equal to the ratio of refractive indices of the two media or their phase velocities.
Snell’s law = sin θ1/ sin θ2 = n2 /n1
The total radiation or the energy emission/unit surface area of a blackbody across different wavelengths per unit time and the fourth power of the blackbody’s thermodynamic temperature are directly proportional.
Wien’s Displacement Law
The blackbody’s radiation curve for various temperatures is maximum for a wavelength inversely proportional to the temperature.
FAQs ablout Laws of Physics
1. How can you broadly classify the laws of Physics?
Basic Physics laws can be categorised in two sections:
1. Classical Physics laws deal with humans, the observable universe, and the environment all around.
2. Atomic Physics specifically focuses on subatomic particles, their decay and interactions (quantum mechanics).
2. What are the different properties of the laws of Physics?
The main properties of laws of Physics that provide valuable information about their nature are as follows:
1. They are true under given conditions.
2. These laws are universal. They do not budge anywhere in the universe.
3. They are simple in representation.
4. The laws stay unaffected by external factors.
5. They are stable and unchanging.
6. They are conservative with respect to their quantity.
7. The laws are theoretically reversible in time.
3. Why is Newton’s first law of motion also called the law of inertia?
The first law is referred to as the law of inertia as it states that each body has an intrinsic property by which it resists changes in its state of rest/motion. The property of resisting a change in contrast to the present state is called inertia.
4. Which laws are derived from approximations, and which ones are from symmetry principles?
General laws are often modified to formulate physical laws. For instance, Newtonian dynamics is a case of special reactivity in low-speed approximations. Newtonian gravitation is general relativity in a low mass approximation.
Symmetries like spacetime and others result in mathematical consequences, which are approximated for the creation of fundamental laws of Physics. For example, the symmetry of time shifts gives birth to the law of conservation of energy. Similarly, the symmetry of space leads to the formulation of the conservation of momentum law.
The above-mentioned laws of Physics are crucial to comprehending various theories and solving numerical problem questions for effective preparation for any Physics exam. Students must understand the laws rather than learn the statements and try to implement them in real-life scenarios.
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