Friday, February 27, 2026

Physics – Last‑Minute Key Definitions

Motion and Forces  

- Uniform Circular Motion: Magnitude of velocity remains constant, but direction changes since acceleration is always perpendicular to velocity.  

- Gravitational Force: Proportional to the product of two point masses and inversely proportional to the square of their separation.  

- Electrical Force: Proportional to the product of two point charges and inversely proportional to the square of their separation.  

- Field of Force: A region where a body experiences a force.  

- Lines of Gravitational Force: Show the direction of gravitational force on a test mass.  

Fields and Potentials  

- Gravitational Field Strength: Gravitational force per unit mass.  

- Electric Field Strength: Electric force per unit charge.  

- Gravitational Field Strength (alternative): Equal to the gravitational potential gradient.  

- Gravitational Potential: Work done in moving a unit mass from infinity to a point.  

- Electric Potential: Work done in moving a unit charge from infinity to a point.  

- Why Gravitational Potential is Negative: It is zero at infinity. Gravitational force is attractive, so as masses approach, potential energy decreases.  

Oscillations  

- Conditions for SHM: Acceleration is directly proportional to displacement and acts in the opposite direction.  

- Damping: Reduction in amplitude due to resistive forces.  

  - Light damping: Amplitude decreases gradually.  

  - Heavy damping: Amplitude decreases quickly.  

- Resonance: Maximum amplitude occurs when the driving frequency equals the natural frequency.  

Thermal Physics  

- Specific Latent Heat: Heat transfer per unit mass during change of state at constant temperature.  

- Specific Heat Capacity: Thermal energy per unit mass per unit temperature change.  

- Internal Energy: Sum of potential and kinetic energies of particles in a system.  

- First Law of Thermodynamics: Increase in internal energy = thermal energy supplied + work done on the system.  

- Pressure–Volume Graph (Ideal Gas): 

  - Total change in internal energy over a complete cycle = 0.  

  - Work done (W = p x Delta V) (if p is constant).  

  - Delta U = Delta q + Delta W  

Kinetic Theory  

- Basic Assumptions:  

  - Particles in continuous random motion.  

  - Negligible volume of particles.  

  - Negligible intermolecular forces.  

  - Collisions are perfectly elastic.  

- Molecular Motion in Gases: Random motion; constant speed in straight lines between collisions.  

Electricity and Magnetism  

- Capacitance: Ratio of charge to potential difference (C = Q/V).  

- Rectification: Conversion of AC to DC.  

- Magnetic Flux Density (B): Force per unit length per unit current, when current is perpendicular to field.  

- Magnetic Flux (Φ): Product of flux density and area perpendicular to the field.  

- Tesla: Equivalent to Newton per Ampere, per metre.  

- Faraday’s Law: Induced emf is directly proportional to the rate of change of magnetic flux linkage.  

- Lenz’s Law: Induced emf opposes the change that caused it.  

Waves and Quantum Physics  

- Vrms (Power Reference): Constant voltage that dissipates the same power as the mean power of alternating voltage.  

- Photon: Quantum of electromagnetic radiation energy.  

- Photoelectric Effect: Emission of electrons from a metal surface when electromagnetic radiation is incident.  

- Work Function Energy: Minimum energy required for an electron to escape the surface.  

- Evidence for Particulate Nature of Light: Photoelectric effect.  

- Evidence for Wave Nature of Matter: Electron diffraction.  

X‑Rays and Ultrasound  

- Production of X‑Rays: Electrons accelerated by a potential difference strike a target; X‑rays are emitted when electrons decelerate.  

- Specific Acoustic Impedance: Product of density and speed of ultrasound in a medium.  

Nuclear and Cosmology  

- Nuclear Binding Energy: Energy required to separate nucleons to infinity.  

- Decay Constant (λ): Probability of decay of a nucleus per unit time.  

- Hubble’s Law: The speed of recession of a galaxy is directly proportional to its distance from the observer.  

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