# Shared Flashcard Set

## Details

Physics Definitions
Physics definitions on word document on moodle
56
Physics
06/07/2011

Term
 Thermal Energy (Heat)
Definition
 Thermal energy (heat) is the non-mechanical transfer of energy between a system and its surroundings.
Term
 Temperature
Definition
 A measure of the average kinetic energy of the molecules in a substance.
Term
 Mole
Definition
 A measurement; one mole of any substance is equal to the amount of that substance that contains the same number of atoms as 0.012 kg of carbon-12 (12C).
Term
 Internal energy
Definition
 The internal energy of a substance is the total potential energy and random kinetic energy of the molecules of the substance.
Term
 Heat Capacity
Definition
 Thermal (Heat) capacity is the energy required to raise the temperature of a body by 1 K
Term
 Specific heat capacity
Definition
 Specific heat capacity is the energy required to raise a unit mass of a substance by 1 K.
Term
 Pressure
Definition
 Pressure is the force per unit normal area (i.e. the area at right angles to the force).
Term
Definition
 This is the number of atoms in 0.012 kg of carbon-12 (12C), i.e. in one mol. It is 6.02 × 10–23.
Term
 Evaporation
Definition
 Process by which individual molecules (the faster-moving ones) leave the surface of a liquid and enter the gas phase. Only takes place at the surface of the liquid at temperatures below the liquid’s boiling point.
Term
 Boiling
Definition
 Boiling is the process by which the molecules of a liquid spontaneous change from the liquid phase into the gas phase throughout the body of the liquid.
Term
 Damping
Definition
 Damping involves a force that is always in the opposite direction to the direction of motion of the oscillating particle and is a dissipative force (i.e. the oscillating particle loses energy).
Term
 Forced oscillations
Definition
 It is possible to force a system to oscillate at any frequency by subjecting it to a changing force at that frequency. Such oscillations are forced oscillations
Term
 Frequency
Definition
 The frequency f is the number of completed oscillations in a given period of time, SI unit: Hz (number of oscillations per second).
Term
 Natural frequency
Definition
 If a system is temporarily displaced from its equilibrium position, it will oscillate at its natural frequency of vibration.
Term
 Resonance
Definition
 Resonance occurs when a system is subject to an oscillating force at exactly the same frequency as the natural frequency of oscillation of the system.
Term
 Simple harmonic motion (SHM)
Definition
 Simple harmonic motion (SHM) is motion where the acceleration of an object is always directed towards a fixed point and is proportional to its displacement from that fixed point.
Term
 Phase difference
Definition
 The phase difference, φ , is a measure of how ‘in step’ different particles are.
Term
 Period
Definition
 The period T is the time taken for one complete oscillation. In other words, it is the time taken for one complete wave to pass any given point.
Term
 Amplitude
Definition
 The amplitude in simple harmonic motion (SHM) is the maximum displacement from the mean position during one oscillation.
Term
 Displacement
Definition
 The displacement of an object is the distance from the origin in a particular direction.
Term
 Travelling waves
Definition
 Progressive (travelling) waves transfer energy. This transfer is achieved by oscillations of the medium through which the wave travels but there is no net motion of the medium.
Term
 Compressions
Definition
 Compressions are the points on a longitudinal wave where all the particles are ‘bunched together’ (high pressure).
Term
 Rarefactions
Definition
 Rarefactions are the points on a longitudinal wave where all the particles are ‘far apart’ (low pressure).
Term
 Crest
Definition
 The crest is the peak of a transverse wave (the point of maximum positive displacement).
Term
 Trough
Definition
 The trough is the lowest point of a transverse wave (the point of maximum negative displacement).
Term
 Transverse waves
Definition
 Transverse waves involve oscillations that are perpendicular to the direction of energy transfer. Light waves (all EM waves) are transverse.
Term
 Longitudinal waves
Definition
 Longitudinal waves involve oscillations that are in the same direction as the direction of energy transfer. Sound waves are longitudinal.
Term
 Electromagnetic waves
Definition
 All electromagnetic waves travel with the same speed in a vacuum (free space). Typical approximate wavelengths are:
Term
 Wave speed
Definition
 The wave speed (in m s–1) is the speed at which the wave pattern passes a stationary observer (i.e. the speed of energy transfer by the wave). V=λF
Term
 Wavelength
Definition
 The wavelength λ is the shortest distance (in m) between two points that are in phase with one another (for example, the distance between adjacent crests on a transverse wave or adjacent compressions on a longitudinal wave).
Term
 Wavefront
Definition
 A surface at right angles to the direction of energy transfer of the wave consisting of points in phase.
Term
 Intensity of a wave
Definition
 The intensity of a wave is the power per unit area that is received by the observer. It is related to the amplitude of the wave.I = P/A
Term
 Acceleration
Definition
 Change in velocity per unit time ORRate of change of velocity.
Term
 Impulse
Definition
 Change in momentum (Δp) ORForce x time during which the force is applied
Term
 Momentum
Definition
 The quantity of motion of a moving body, measured by:mass x velocity
Term
 Power
Definition
 The rate of working,Work/Time
Term
 Specific latent heat of fusion
Definition
 The amount of (thermal) energy needed to convert a unit mass of a solid substance into a liquid at the melting temperature of the substance / at constant temperature.
Term
 Specific Latent Heat of Vaporization
Definition
 Quantity of thermal energy/heat required to convert unit mass / mass of 1 kg of liquid to vapour/gas; With no change of temperature / at its boiling point.
Term
 Speed
Definition
 Average speed: is the distance traveled divided by the time taken.
Term
 Instantaneous speed
Definition
 Rate of change of distance at a given instant (in time)
Term
 Velocity
Definition
 Total displacement traveled divided by the time taken
Term
 Newton’s 1st Law
Definition
 Every object continues in a state of rest or uniform motion in a straight line unless acted upon by an external force.
Term
 Newton’s 2nd Law
Definition
 The rate of change of momentum of a body is proportional to the resultant force and occurs in the direction of the force.ORThe acceleration of a body is proportional to the resultant force and occurs in the direction of the force.
Term
 Newton's 3rd Law
Definition
 When two bodies A and B interact, the force that A exerts on B is equal and opposite to the force that B exerts on A.
Term
 Molar Mass
Definition
 The mass of one mole of a substance.
Term
 Specific Latent Heat
Definition
 Amount of energy per unit mass absorbed or released during a change of phase. (Solid->Liquid = fusion)
Term
 Kinetic Theory of Gases (Assumptions of Ideal Gases)
Definition
 1) Newton's laws apply to molecular behavior.2) No intermolecular forces (except in collisions).3) The molecules are in random motion.4) The collisions between the molecules are elastic.5) No time spent on collisions in comparison to time spent between collisions.6) Volume of individual gas molecules negligible when compared to volume of container.
Term
 Angular Frequency
Definition
 Measure of rate of motion denoted by ω. Important for SHM.
Term
 The Principle of Superposition.
Definition
 When two waves of the same type meet, the resulting disturbance at any point and at any time where the waves meet is just the vector sum of the disturbances that would have been produced by each of the individual waves.
Term
 Destructive Interference
Definition
 When two identical waves meet at a point and the waves are exactly (180°) out of phase, the resulting wave has zero amplitude – the two waves cancel each other.
Term
 Constructive Interference
Definition
 When two identical waves meet at a point and the waves are exactly in phase, the resulting wave has twice the amplitude of either of the original waves.
Term
 Reflection at a Boundary
Definition
 A wave reflected at the boundary between two media stays in its original medium. Its direction of travel is such that the incident angle (the angle between the incident ray and the normal) and the reflected angle (the angle between the reflected ray and the normal) are equal.
Term
 Refraction at a Boundary
Definition
 A wave transmitted across the boundary between two media moves from one medium into the other. Its direction of travel changes as a result of refraction as calculated by Snell’s law.
Term
 Diffraction
Definition
 Diffraction is the phenomenon of the spreading of a wave after an aperture or obstacle. It is the process by which wave energy is received in the geometric shadow region after an obstacle or gap.
Term
 Snell’s Law
Definition
 When a wave is refracted between two media, the ratio of the angle of incidence to the angle of refraction is a fixed constant that depends on the speeds of wave in each media.n1/n2 = sin(θ1) / sin (θ2)
Term
 Path difference
Definition
 The difference in the total lengths of the two routes from source to that point. (Interference often takes place at a given point in space as a result of there being two different routes for the wave energy to travel from source to that point.)
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