⚙️ PHYSICS – SUMMARY NOTES

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🧠 1. What is Physics?

Physics is the branch of science that deals with matter, energy, and their interactions.
It explains the laws of nature and fundamental forces governing the universe.

Word origin: Physis (Greek) = Nature

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🧭 2. Branches of Physics

Branch	Study Area
Mechanics	Motion and forces
Thermodynamics	Heat and work
Electromagnetism	Electric & magnetic fields
Optics	Light and vision
Waves & Sound	Oscillations and vibrations
Modern Physics	Atoms, nuclei, quantum theory
Astrophysics	Space and celestial objects
Electronics	Flow of electrons, circuits

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📏 3. Physical Quantities & Units

Quantity	SI Unit	Symbol
Length	Meter	m
Mass	Kilogram	kg
Time	Second	s
Electric Current	Ampere	A
Temperature	Kelvin	K
Luminous Intensity	Candela	cd
Amount of Substance	Mole	mol

Derived Units: Area (m²), Volume (m³), Velocity (m/s), Force (N), Energy (J).

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⚖️ 4. Laws of Motion (Newton’s Laws)

1. First Law (Inertia):
   A body remains at rest or in uniform motion unless acted upon by an external force.
2. Second Law:F=m×aF=m×a(Force = mass × acceleration)
3. Third Law:
   For every action, there is an equal and opposite reaction.

Momentum: p=m×vp=m×v

Law of Conservation of Momentum: Total momentum remains constant in a closed system.

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⚙️ 5. Work, Power, and Energy

Concept	Formula	Unit
Work (W)	W=F×dcos⁡θW=F×dcosθ	Joule (J)
Power (P)	P=WtP=tW​	Watt (W)
Energy	Ability to do work	Joule (J)

Types of Energy

• Kinetic Energy: KE=12mv2KE=21​mv2
• Potential Energy: PE=mghPE=mgh

Law of Conservation of Energy:
Energy can neither be created nor destroyed, only transformed.

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🌍 6. Gravitation

Newton’s Law of Gravitation:F=Gm1m2r2F=Gr2m1​m2​​

Where:
G = Gravitational constant = 6.67×10−11Nm2/kg26.67×10−11Nm2/kg2

Weight (W): W=mgW=mg

Acceleration due to gravity (g): 9.8 m/s29.8m/s2

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🌡️ 7. Heat and Thermodynamics

Concept	Formula / Law	Meaning
Temperature	Measure of hotness or coldness
Heat Transfer	Conduction, Convection, Radiation
Specific Heat (c)	Q=mcΔTQ=mcΔT
Latent Heat (L)	Q=mLQ=mL

Laws of Thermodynamics

1. Zeroth Law: If A = B and B = C → A = C (Thermal equilibrium)
2. First Law: ΔU=Q−WΔU=Q−W (Energy conservation)
3. Second Law: Heat flows from hot → cold naturally.

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💡 8. Light (Optics)

Laws of Reflection:

1. Angle of incidence = Angle of reflection
2. Incident ray, reflected ray, and normal lie in the same plane.

Laws of Refraction (Snell’s Law):sin⁡isin⁡r=n21sinrsini​=n21​

Lens Formula:1f=1v−1uf1​=v1​−u1​

Mirror Formula:
Same as lens but sign conventions differ.

Magnification (m): m=h2h1=vum=h1​h2​​=uv​

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🎵 9. Sound

• Sound is a mechanical wave requiring a medium.
• Speed of sound in air: ≈ 343 m/s (at 25°C)

Important Terms:

Term	Meaning
Frequency (f)	No. of vibrations per second (Hz)
Amplitude	Maximum displacement
Wavelength (λ)	Distance between two crests
Velocity	v=fλv=fλ

Human audible range: 20 Hz – 20,000 Hz
Ultrasound: Above 20,000 Hz

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⚡ 10. Electricity

Ohm’s Law:V=IRV=IR

(V = potential difference, I = current, R = resistance)

Power (P): P=VI=I2R=V2RP=VI=I2R=RV2​

Energy (E): E=P×tE=P×t

Series Circuit: Req=R1+R2+R3Req​=R1​+R2​+R3​
Parallel Circuit: 1Req=1R1+1R2+1R3Req​1​=R1​1​+R2​1​+R3​1​

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🧲 11. Magnetism and Electromagnetism

Magnetic Field (B): Region around a magnet where force acts.

Right-Hand Thumb Rule:
Direction of magnetic field = curl of fingers around current direction.

Electromagnetic Induction (Faraday’s Law):
Change in magnetic flux → induces EMF (voltage).

Fleming’s Rules:

• Left-hand rule: Direction of force in motor.
• Right-hand rule: Direction of induced current in generator.

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💥 12. Modern Physics

a. Structure of Atom

• Rutherford Model: Nucleus at center, electrons revolve.
• Bohr Model: Electrons in quantized orbits (energy levels).

Atomic Number (Z): No. of protons
Mass Number (A): Protons + Neutrons

b. Radioactivity

Spontaneous emission of α, β, γ rays.

Half-life (t½): Time taken for half of radioactive atoms to decay.

c. Nuclear Reactions

• Fission: Splitting of heavy nuclei (e.g., U-235)
• Fusion: Combining of light nuclei (e.g., H → He)

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🔋 13. Electronics and Communication

Concept	Description
Semiconductors	Materials with partial conductivity (e.g., Si, Ge)
Diode	Allows current in one direction
Transistor	Amplifier/switch device
Logic Gates	AND, OR, NOT, NAND, NOR
Communication System	Transmitter → Channel → Receiver

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🧭 14. Waves and Oscillations

Term	Formula / Concept
Period (T)	Time for one oscillation
Frequency (f)	f=1/Tf=1/T
Wave Speed	v=fλv=fλ
Types	Transverse & Longitudinal

Simple Pendulum: T=2πlgT=2πgl​​

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🌍 15. Universe and Space Physics

Concept	Description
Big Bang Theory	Universe originated from an explosion
Galaxies	Large systems of stars
Solar System	8 planets revolve around the Sun
Satellite	Artificial (e.g., INSAT) or natural (Moon)
Black Hole	Region of extremely high gravity

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🔢 16. Important Constants

Quantity	Symbol	Value
Gravitational Constant	G	6.67×10−116.67×10−11 Nm²/kg²
Speed of Light	c	3.0×1083.0×108 m/s
Planck’s Constant	h	6.63×10−346.63×10−34 J·s
Avogadro’s Number	Nₐ	6.022×10236.022×1023
Electron Charge	e	1.6×10−191.6×10−19 C

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📚 17. Summary Table

Topic	Key Formula / Concept
Motion	v=u+at,s=ut+12at2v=u+at,s=ut+21​at2
Force	F=maF=ma
Energy	KE=12mv2KE=21​mv2, PE=mghPE=mgh
Work Power	W=FdW=Fd, P=W/tP=W/t
Gravitation	F=Gm1m2r2F=Gr2m1​m2​​
Heat	Q=mcΔTQ=mcΔT
Electricity	V=IRV=IR
Waves	v=fλv=fλ
Optics	1/f=1/v−1/u1/f=1/v−1/u
Radioactivity	N=N0e−λtN=N0​e−λt

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🧩 18. Laws & Principles at a Glance

Law / Principle	Scientist
Laws of Motion	Newton
Universal Gravitation	Newton
Law of Energy Conservation	Joule
Ohm’s Law	Ohm
Law of Reflection	Snell
Faraday’s Law	Faraday
Photoelectric Effect	Einstein
Law of Floatation	Archimedes

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✅ 19. Physics in Daily Life

• Electricity in homes (Ohm’s Law)
• Car brakes (Friction & motion)
• Airplanes (Bernoulli’s principle)
• Satellites (Gravitation)
• Sound systems (Waves & resonance)

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🧭 20. Summary

Area	Core Idea
Mechanics	Motion & forces
Energy	Work, heat, conservation
Electricity	Current, voltage, resistance
Light	Reflection, refraction, lenses
Waves	Sound & oscillations
Modern Physics	Atoms, radiation, quantum
Universe	Space & cosmology