DEFINITIONS /STATEMENTS/PRINCIPLES/ CHARACTERISTICS – PHYSICS AS

Define densityMass per unit volume

Define pressureForce per unit area

Define work doneProduct of force and distance moved by force in the direction of the force

PowerWork done per unit time

Define displacementDistance moved from a fixed point in a specified direction

State the difference between a scalar quantity and a vector quantityScalar: has magnitude onlyVector: has magnitude and direction

Define accelerationRate of change of velocity

Distinguish the moment of a force and the torque of a coupleMoment: force x perpendicular distance of force from pivotTorque: magnitude of one force x perpendicular distance between the two forces

Distinguish between systematic errors and random errorsSystematic:

Random:

Define potential energyStored energy available to do work

Distinguish between gravitational potential energy and elastic potential energyGravitational: due to position of mass or distance of mass from one point to anotherElastic: due to deformation

Constant error in all readings Cannot be eliminated by

averaging Error in measuring instrument Readings scattered equally about

true value Can be eliminated by averaging Error due to observer

The Principle of conservation of momentumThe sum of momentum in any direction is constant in a closed system provided that there is no external force acting on the system.

What is meant by centre of gravity?It is the point where the whole weight of the body may be considered to act

Distinguish between the mass of a body and its weightMass: measure of body’s inertia to changes in motionWeight: force of gravity

The conditions for a body to be in equilibrium No resultant force in any direction No resultant moment about any point

Define the resistance of a resistorRatio of potential difference to current

ThermistorAs temperature rises, resistance of thermistor decreases

Define electric field strengthForce per unit positive charge on a small test charge

Boiling and evaporationSimilarity: both involve a phase change from liquid to gasDifferences:

What is meant by Brownian movement?Haphazard and random movement of smoke particles

Describe the structure of

Define Tensile stress: stress = force / cross sectional area Tensile strain: strain = extension / original length The Young modulus = stress / strain

Strain energy (elastic potential energy)It is the ability to do work as a result of a change of shape of an object

Internal energy of a substanceIt is the sum of random kinetic and potential energies of the atoms of the substances

Evaporation takes place at the surface – Boiling occurs in the body of the liquid

Evaporation occurs at all temperature – boiling occurs at one temperature (the boiling point)

a metal : lattice of atoms in regular pattern that repeats itself within crystal

a polymer : has long chain of molecules, each chain consists of units that repeat themselves

What is an elastic deformation?It is the change of shape such that when the deforming force is removed, the object returns to its original shape

State the principle of SuperpositionWhen two or more waves meet, the resultant displacement is the sum of individual displacements

Explain what is meant by A transverse wave: vibrations in plane normal to direction of energy propagation Polarization: vibrations in one direction normal to direction of propagation

Conditions for two waves to interfere Both waves are of same type (longitudinal or transverse) They must meet at a point They should have the same direction of polarization

Explain what is meant by Interference: when two or more waves meet at a point, there is a change in overall

displacement Coherence: constant phase difference between waves

State what is meant by The frequency of a progressive wave – it is the number of oscillations per unit time

of the source Speed of a progressive wave – it is the speed at which energy is transferred

State the effect on the appearance of the fringes in a double-slit experiment when

The separation of the slits, a is increased-smaller separations of fringes, no change in brightness

The width of each slit is increased but the separation, a remains constant Same fringe separation Maxima- brighter Minima – no change

Explain why a wave is said to be ‘stationary’It does not transfer energy along the wave

What is meant by the speed of a stationary wave?When two waves traveling in opposite directions interfere, a stationary wave is formed. Speed is then the speed of one of these waves

What is meant by the diffraction of wave?The bending of wave into geometrical shadow when the wave is incident at an aperture

What is an antinode?It is the position along the wave where amplitude of vibration is a maximum

State the features that are common to electromagnetic waves All have same speed in vacuum All can be polarized All undergo diffraction/interference/superposition All can be reflected/refracted All are progressive

Distinguish between an α-particle and a β-particle α-particle contains 2 protons & 2 neutrons, β-particle an electron α speed < β speed α mass > β mass α ionizing power >> β ionizing power α positive, β negative

State the nature of an α-particleIt is a helium nucleus

Explain what is meant by radioactive decayThe nucleus emits α- or β- particle, or γ-rays

Spontaneous decayDecay is not affected by environmental factors

Random decayNucleus has constant probability of decay in a given time

State the deductions from the α-scattering experiment when most α-particles were deviated through angles of less than 10°

- nucleus is small in comparison to size of atom when a very small proportion of the α-particles were deviated through

angles of greater than 90°- nucleus is dense and charged

State the results of the α-scattering experiment most α-particles are deviated through small angles few α-particles deviated through angles greater than 90°

Define isotopesAtoms of the same element with the same number of protons but different number of neutrons