H2 Physics Definitions

Basic Assumption of Kinetic Theory of Gases (5/5)

The intermolecular forces of attraction between molecules are negligible.

Simple Harmonic Motion

Motion of a body is such that its acceleration is proportional to its displacement from its equilibrium position and its acceleration is always opposite in direction to its displacement from the equilibrium.

Interference

Effect that occurs when two or more waves overlap; the displacement at each point in the overlapping region is the vector sum of the displacements of the overlapping waves.

Conditions for Observable Interference (3/5)

Waves from the sources must overlap.

Excited State/Excitation

Electron(s) in an atom are at the higher energy level(s) rather than at the lowest energy level(s).

Scalar Quantities

Physical quantities that only have a magnitude.

Vector Quantities

Physical quantities that have both a magnitude and a direction in space.

Systematic Error

Leads to readings that are consistently more or consistently less than the true value.

Random Error

Gives rise to a scatter of readings about a mean value.

Accuracy

A measure of how close a reading or the average of a set of readings is to the true value.

Precision

A measure of how small the spread of repeated readings about the average value.

Displacement

Distance from a fixed reference point in a specified direction.

Distance

Length between two points measured along the straight line joining two points.

Velocity

Rate of change of displacement.

Speed

Distance travelled per unit time.

Acceleration

Rate of change of velocity.

Newton's First Law

A body stays at rest or continues to move at constant velocity unless a resultant force acts on it.

Newton's Second Law

The rate of change of momentum of a body is proportional to the resultant force acting on it and it is in the direction of the resultant force.

Newton's Third Law

Whenever body A exerts a force on body B, body B exerts an equal but oppositely directed force of the same kind on body A.

Momentum

Momentum of a body is the product of its mass and velocity.

Impulse

Product of the force and the duration for which the force acts.

Head-on Collision

The velocity vectors of the two bodies are always parallel to the straight line connecting the centre of mass of each of the bodies.

Hooke's Law

Within the limit of proportionality, the extension produced in a material is directly proportional to the force applied.

Centre of Gravity

The point at which the whole weight of the body appears to act.

Moment

Product of the force and the perpendicular distance from the line of action of the force to the pivot.

Couple

A pair of forces acting on the same body that are equal in magnitude but opposite in direction and produce rotation only.

Torque

The turning effect of a couple is equal to the product of one of the forces of the couple and the perpendicular distance between the lines of action of the forces.

Principle of Moments

For a body in rotational equilibrium, the sum of clockwise moments about any axis of rotation (or pivot) must be equal to the sum of anti-clockwise moments about the same axis (or pivot).

Upthrust

A force equal in magnitude and opposite in direction to the weight of the fluid displaced by a submerged or floating object.

Work Done

Product of the force and displacement in the direction of the force.

Power

Work done per unit time.

Angular Displacement

Ratio of the arc length to the radius of a circle.

Radian

The angle subtended at the centre of a circle by an arc equal in length to the radius.

Field of Force

A region of space in which a force is experienced.

Newton's Law of Gravitation

The mutual gravitational force of attraction between two point masses is directly proportional to the product of their masses and inversely proportional to the square of their distance apart.

Gravitational Field Strength

Gravitational force exerted per unit mass placed at that point.

Escape Velocity

Minimum initial speed required by an object to travel from a point in the gravitational field to infinity.

Geostationary Orbit

A satellite in geostationary orbit remains above a fixed point on the Earth's equator.

Electric Field

A region of space where an electric force acts on a stationary charge placed at any point within the region.

Electric Field Strength

Electric force exerted per unit positive charge on a small stationary test charge placed at that point.

Phase (SHM)

State of the oscillation of a body at a particular time.

Phase Difference (Waves) (One Wave Two Particles)

Phase difference between two particles along a wave is the measure of the fraction of a cycle that one particle is moving out of step with the other.

Intensity

Power per unit area transferred across an area perpendicular to the direction of energy transfer.

Period (AC)

Time taken for the current (or voltage) to complete one cycle.

Decay Constant

Probability per unit time of the decay of a nucleus.

Principle of Conservation of Momentum

In the absence of an external resultant force acting on a system of interacting bodies, the total momentum of the system remains constant.

Angular Velocity

Rate of change of angular displacement.

Gravitational Field

A region of space where a gravitational force acts on a mass placed within the region.

Gravitational Potential Energy

The work done by an external agent on the mass in moving it from infinity to that point.

Gravitational Potential

Work done per unit mass in bringing a small test mass from infinity to that point.

Coulomb's Law

Magnitude of the electrostatic force between two point electric charges is directly proportional to the product of the magnitudes of each charge and inversely proportional to the square of the distance between the charges.

Electric Potential

Work done per unit positive charge in bringing a small test charge from infinity to that point.

Zeroth Law of Thermodynamics

When two or more objects are in thermal equilibrium, they must be at the same temperature and there is no net transfer of thermal energy between them when they are placed in thermal contact.

Absolute Zero

The temperature at which all substances have the minimum internal energy.

Absolute/thermodynamic temperature scale

Temperature scale that is independent of the property of any particular substance and has an absolute zero.

Ideal Gas

A gas which obeys the equation of state pV = nRT.

Basic Assumption of Kinetic Theory of Gases (1/5)

Perfectly elastic collisions between the gas molecules and the walls of the container.

Basic Assumption of Kinetic Theory of Gases (2/5)

Total volume of the gas molecules is negligible compared to the volume occupied by the gas.

Basic Assumption of Kinetic Theory of Gases (3/5)

The duration of a collision is negligible compared with the time between collisions.

Basic Assumption of Kinetic Theory of Gases (4/5)

There are a large number of molecules in constant random motion.

Specific Heat Capacity

Thermal energy transferred per unit mass per unit change in temperature.

Specific Latent Heat

Thermal energy transferred per unit mass during the change of state at constant temperature.

Specific Latent Heat of Fusion

Thermal energy transferred per unit mass during the change of state between solid and liquid at constant temperature.

Specific Latent Heat of Vaporisation

Thermal energy transferred per unit mass during the change of state between liquid and gas at constant temperature.

Internal Energy of a System

Sum of the random distribution of kinetic and potential energies associated with the molecules of the system.

First Law of Thermodynamics

Increase in internal energy of the system is equal to the sum of the heat supplied to the system and the work done on the system.

Amplitude (SHM)

Magnitude of the maximum displacement from its equilibrium position.

Period (SHM)

Time taken for one complete oscillation.

Frequency (SHM)

Number of oscillations per unit time.

Angular Frequency

Product of the frequency of oscillation and 2π.

Phase Difference (for two oscillators)

Difference in the state of oscillation between two oscillators at a particular instant.

Phase Difference (for one oscillator)

Difference in the state of oscillation for one oscillator at two instances in time.

Free Oscillations

A particle is said to undergoing free oscillations if it is oscillating at its natural frequency/if the only force acting on it is the restoring force

Damping

The decrease in the amplitude of oscillation with time due to energy loss.

Forced Oscillations

The application of a periodic driving force to a system to make it oscillate at the frequency of the applied force rather than its natural frequency. The driving force provides a constant driving frequency and a constant amplitude.

Resonance

When the frequency of the driving force equals the natural frequency of the oscillating system. Maximum energy transfer occurs and the amplitude of oscillations of the system is at its maximum.

Displacement (Waves)

Distance in a specified direction from its equilibrium position of a particle on a wave.

Amplitude (Waves)

Magnitude of the maximum displacement from its equilibrium position of a particle on a wave.

Period (Waves)

Time taken for a particle in the wave to complete one oscillation.

Phase Difference (Waves) (Between 2 Waves)

Phase difference between two waves is the measure of the fraction of a cycle that one wave (or one particle) is moving out of step with the other.

Wavelength

Shortest distance between two points on a progressive wave which are oscillating in phase.

Wave Speed

Distance travelled by the wave per unit time.

Progressive Waves

Energy is transferred in the direction of wave propagation by the oscillations of the particles in the medium. The waveform appears to be moving although the particles in the medium do not get transported along the wave.

Stationary Waves

There is no net transfer of energy, the waveform does not appear to travel.

Transverse Waves

The plane of oscillations of the particles of the medium are at right angles to the direction of transfer of energy.

Longitudinal Waves

Particles in the medium oscillate along an axis parallel to the direction of transfer of energy.

Wavefront

A wavefront is the imaginary line joining points on a wave with the same phase.

Unpolarised Transverse Wave

A wave where the oscillations are in all directions in a plane normal to the direction of energy transfer.

Plane-polarised Transverse Wave

A wave where the oscillations are confined to one direction only in a plane normal to the direction of energy transfer.

Principle of Superposition

When two or more waves meet at a point, the resultant displacement at that point is equal to the vector sum of the displacements due to the individual waves at that point.

Coherence

Constant phase difference between the waves (or sources of waves) with time.

Path Difference

Difference in distances that one wave travels compared with another wave from the sources to reach a particular point.

Conditions for Observable Interference (1/5)

The sources or waves are coherent.

Conditions for Observable Interference (2/5)

Waves from sources have similar amplitudes.

Conditions for Observable Interference (4/5)

Waves are of the same type.

Conditions for Observable Interference (5/5)

For polarised transverse waves, waves must have the same plane of polarisation.

Diffraction

Spreading of waves after passing through a slit or around the edge of an obstacle.

Limit of Resolution or Resolving Power of an Aperture

Occurs when the central maximum of the second source coincides with the first minimum of the first source.

Electric Current

Rate of flow of positive charges.

Potential Difference (between two points)

Amount of energy per unit charge converted from electrical energy to other forms of energy when the charge passes between the two points.