physics definitions

mass defect

the difference between the total mass of the separate nucleons in a nucleus and the combined mass of the nucleus

binding energy

the energy required to separate the nucleons in a nucleus to infinity. it is also the energy equivalent of the mass defect of a nucleus

binding energy per nucleon

average energy per nucleon needed to separate a nucleus into its constituent nucleons to infinity

nuclear fission

the splitting of a heavy nucleus into two lighter nuclei of approximately the same mass

nuclear fusion

the process where two light nuclei combine to form a nucleus of greater mass

radioactive decay

a spontaneous and random process in which an unstable nucleus emits alpha particles, beta particles or gamma radiation to become more stable

random

a random process is one in which it cannot be predicted which nucleus will decay next

spontaneous

a spontaneous process is one which is not triggered or affected by external factors such as temperature or pressure

exponential decrease

a situation where a quantity reduces at a rate proportional to its current value

decay law

for a large number of nuclei, the rate at which a particular decay process occurs in a radioactive sample is proportional to the number of undecayed radioactive nuclei present

decay constant

probability per unit time of decay of a nucleus

activity of a radioactive source

the number of nucear disintegrations per unit time in the source

count rate

rate at which emissions from a radioactive source are detected

half life

average time taken for the number of undecayed nuclei to be reduced to half its original number

simple harmonic motion

the acceleration is directly proportional to the displacement from the equilibrium position and the acceleration is always directed towards the equilibrium positio

oscillation

repetitive back and forth motion of an object along the same path

free oscillation

there is neither resistive forces nor driving forces acting on the system. total energy is always constant and it oscillates with a constant amplitude. the object oscillates with a frequency called its natural frequency.

damped oscillation

one that experiences resistive forces and the oscillating system loses energy until it comes to a stop

forced oscillation

one that is driven by an external periodic driving oscillator or river. there is continuous energy input to the oscillating system by the driver and the system oscillates at the frequency of the driver

resonance

resonance is the phenomenon in which there is a maximum transfer of energy from the driver to the oscillating system in a forced oscillation. the oscillating system achieves maximum amplitude during resonance. for an undamped system, resonance occurs when the driving frequency equals the natural frequency of the oscillating system

transverse wave

a wave in which the oscillations of the particles in the waves are perpendicular to the direction in which the energy of the wave is travelling

longitudinal waves

a wave in which the oscillations of the particles in the wave is along or parallel to the direction in which the energy of the wave is travelling

intensity of a wave

rate of flow of energy per unit area perpendicular to the direction of the wave

polarisation

polarisation is a process by which a wave’s oscillations are made to occur in a single plane only

principle of superposition

when waves meet, the actual displacement is the vector sum of the separate displacements of the individual waves, and each wave proceeds as though no other waves exist

interference

interference is the result of superposition of wavetrains from a finite number of coherent sources

coherent sources

sources that have a constant phase difference

stationary wave

it is formed from the superposition of two progressive wavetrains of equal amplitude and frequency and wavelength travelling with the same speed is opposite directions over the same space

wavetrain

a succession of wave cycles moving at the same speed and typically having the same wavelength

diffraction

it is the spreading of waves when they pass through an opening or around an obstacle

rayleigh’s criterion

it states that the images of two point sources can just barely be distinguished from each other if the central maximum of one diffraction pattern falls on the first minimum of the other one

coulomb’s law

coulomb’s law states that the magnitude of the electric force F between two point charges Q1 and Q2 is proportional to their charges and inversely proportional to the square of their separation r

newton’s law of gravitation

states that two point masses attract each other with a force that is proportional to the product of their masses and inversely proportional to the square of the separation between them

electric field

an electric field is a region of space in which a charge placed in that region experiences an electric force

grav field

a gravitational field is a region of space in which a mass experiences a force

efield strength

it is the electric force exerted per unit positive charge acting on a test charge placed at that point

gfield strength

the gravitational force experienced per unit mass acting on a small test mass at that point

electric potential energy

it is the work done by an external agent in bringing the charge from infinity to that point without any change in kinetic energy)

grav potential energy

it is the work done by an external agent in bringing te mass from infinity to that point

electric potential

it is the work done per unit positive charge in bringing a small test charge from infinity to that point by an external agent without any change in kinetic energy

gravitational potential

it is the work done per unit mass by an external agent in bringing a small test mass from infinity to that point

thermal equilibrium

when two bodies are in thermal equilibrium, there is no net transfer of thermal energy between the bodies in thermal contact and the bodies are at the same temperature

assumptions of the kinetic theory of gases

1. any gas is made up of a large number of particles

2. the particles are in constant and random motion

3. the particles make perfectly elastic collisions among themselves and with the wall of the container ( no loss of KE when particles collide)

4. the volume of each particle is negligible compared to the volume of the gas

5. the forces between the particles are negligible except during the time of collision

6. the duration of collisions is negligible compared with the time interval between collisions

internal energy of a system

it is the sum of random distribution of kinetic energy and potential energy of all the atoms or molecules

specific heat capacity of a substance

it is the thermal energy per unit mass to raise the temperature of a substance by one degree Kelvin

specific atent heat of fusion

it is the amount of thermal energy required per unit mass to change a substance from the solid phase to the liquid phase at constant temperature

specific latent heat of vaporisation

it is the amount of thermal energy required per unit mass to change a substance from the liquid phase to the vapor phase at constant temperature

first law of thermodynamics

it states that the increase in internal energy is equal to the sum of heat supplied to the system and the work done on the system