AS Definitions and Laws Flashcards
Acceleration
Rate of change of velocity.
Recall formula: a = Δv/Δt
Accuracy
Measurement is accurate if it is close to the true value.
Alpha particle
A helium nucleus.
Has 2 protons and 2 neutrons.
Stopped by paper.
Most ionising.
Amplitude
Maximum displacement from the equilibrium position to the crest.
Antinode
Point of maximum displacement in a stationary wave.
Base quantities
Physical quantities that are used to define other physical quantities. mass length, time temperature current amount of substance
Base units
Units of base quantities; kg m s K A mol.
Beta particle
A fast moving electron or positron.
Stopped by a few cm of aluminium.
Less ionising compared to alpha particle.
Centre of gravity
Point at which the whole weight of the body may be considered to act.
Coherence
- Constant phase difference between waves.
2. Waves have same frequency.
Constructive interference
Occurs when two waves are in phase. Condition for constructive interference: Path difference = n(lambda), where n = 0, 1, 2, …... or Phase difference = n x 2(pi) radians.
coulomb (C)
1 C of charge passes a point when a current of 1 A flows for 1 s.
(Recall formula: Q = It)
Couple
Two parallel forces which are equal but opposite. Their lines of action do not meet.
Current
Rate of flow of charged particle.
Recall formula: Q = It
Density
Mass per unit volume.
Recall formula: density = M/V
Destructive interference
Occurs when the two waves are out of phase.
Condition for destructive interference:
Path difference = (n + ½)lambda, where n = 0, 1, 2, ……
or
Phase difference = (n + ½)(2 x pi) radians
Diffraction
The spreading out (or bending) of waves when they pass through a gap (or when they pass the edge of an object).
Diffraction grating formula
n(lambda) = d sin (theta)
Diode
A device that allows current to flow through it in one direction only.
Displacement
Distance from a fixed point in a specified direction.
Ductile material
A material that can be drawn into a thin wire without breaking.
Efficiency
Efficiency = useful energy output/ total energy input
or
Efficiency = useful power output/ total power input
Elastic deformation
When a force is applied, the material changes its shape/ size. When the force is removed, the material returns to its original shape/ size.
Elastic collision
A collision in which momentum and kinetic energy are conserved.
Total k.e. before collision = total k.e. after collision.
In a perfectly elastic collision,
relative speed of approach = relative speed of separation.
Elastic limit
When extended beyond its elastic limit, a material will undergo plastic deformation (ie. it will not return to its original shape/ size after load is removed).
Elastic potential energy
Ability to do work due to deformation of an object. Also known as strain energy.
E = ½ Fe
or
E =
Electric field strength
Definition: force per unit positive charge.
Unit:
Electric field strength between parallel plates
Electric field is uniform between two parallel plates, ie. electric field strength is the same everywhere between the plates.
Formula: E = V/d
Electromotive force (e.m.f.) of a cell
Definition: Energy transferred by the cell in driving a unit charge round a complete circuit.
Electron volt (eV)
A unit of energy.
Definition: The energy transferred when an electron moves through a p.d. of 1 V.
1 eV = 1.60 x 10^-19 J
Energy
A measure of the stored ability of a body to do work.
Equilibrium
A body is in equilibrium if
- no resultant force in any direction
- no resultant moment about any point.
Force
Rate of change of momentum.
F =
Frequency
Number of oscillations per unit time.
Gamma radiation
Electromagnetic waves. Speed of 3.00 x 10^8 m s^-1.
Gravitational potential energy
Ability to do work due to height/position of the mass.
Homogeneous equation
Equation is homogeneous if all the terms have the same base units.
Impulse
Product of the force acting on a body and the time interval over which the force acts (ie. it is equal to the change in momentum).
Inelastic collision
A collision in which momentum is conserved but kinetic energy is not conserved.
Intensity of a wave
Power incident on a surface per unit area.
Rate of flow of energy per unit area perpendicular to the direction of the wave.
Interference
When two or more waves meet at a point, the resultant displacement is the sum of the individual displacements.
Conditions for interference:
- Same type of waves, ie. both transverse or both longitudinal
- Waves meet at a point
- Waves have same direction of polarisation.
Internal energy
Sum of the random distribution of the kinetic and potential energies of the particles in the substance.
K.E. of particles is proportional to temperature and P.E. of particles increases if they are further apart.
Isotope
Nuclei with the same number of protons but different number of neutrons.
Light-dependent resistor
Resistance of LDR decreases as light intensity increases.
Limit of proportionality
When loaded beyond the limit of proportionality, extension will no longer be proportional to the load.
Longitudinal wave
A wave in which vibrations are parallel to the direction of energy travel.
Mass
A measure of a body’s inertia to changes in motion.
Moment of a force
Product of force and the perpendicular distance of force from the pivot.
Momentum
Product of mass and veloctiy.
Define the newton (N)
1 N is the force that will give a mass of 1 kg an acceleration of 1 m s^-2.
Node
A point on a stationary wave where displacement is zero.
Nucleon number
The number of protons and neutrons in a nucleus. Also called mass number.
ohm
Definition: The resistance between two points is 1 ohm if a current of 1 A flows when there is a p.d. of 1 V between the points.
Path difference
The extra length travelled by a wave when it is compared to another wave.
Phase difference
A measure of the extent to which a wave is out of phase with a reference wave.
Formula?
Plastic deformation
When a force is applied, the material changes its shape/ size. When the force is removed, the material does not return to its original shape/ size.
Potential difference
Definition: The p.d. between two points is the energy transferred (or work done) when unit charge moves between those points.
Power
Work done per unit time.
For a body moving at constant velocity, P = Fv
Precision
Measurements are precise if they are close to one another.
Pressure
Force per unit area.
Pressure in a fluid
p = density x g x h
Progressive wave
Wave that carries energy from one point to another through vibrations within the medium.
Proton number
The number of protons in a nucleus. Also called atomic number.
Random error
Random errors will result in readings being scattered about the true value. Can be reduced by averaging. Example of random error: diameter of wire is not uniform.
Resistance
Definition: Ratio of p.d. between the points to the current flowing between them.
Resistivity
R = (resistivity x length) / cross-sectional area
Scalar quantity
Quantity with magnitude only. Eg. mass, density, pressure, speed, distance.
Semiconductor
For a semiconductor, resistance decreases as temperature increases. This is because the atoms in a semiconductor release electrons when temperature is higher.
Speed
Distance travelled per unit time.
Spring constant
Force per unit extension.
Stationary wave (or standing wave)
Stationary wave is formed by superposition of two waves of same type and same frequency that are travelling in opposite directions (eg. when incident wave and reflected wave meet, they superpose). Speed of stationary wave is the speed of the incident wave.
Strain
Ratio of extension to the original length. No unit.
Stress
Force per unit cross-sectional area.
Systematic error
Will result in constant error in all readings. It cannot be eliminated by averaging. Eg. zero error of micrometer screw gauge.
Terminal velocity
Constant velocity of a falling object, when weight = air resistance + upthrust.
Thermistor
A semiconductor device. Its resistance decreases as its temperature increases.
Torque of a couple
Product of one force and the perpendicular distance between the two forces.
Transverse wave
A wave in which vibrations are perpendicular to the direction of energy travel.
Ultimate tensile stress
The maximum stress for a material.
Upthrust
The vertical force exerted by a fluid on an object when it is immersed in the fluid. It is due to differences in pressure at different depths.
Vector quantity
Quantity with magnitude and direction. Eg. velocity, force, momentum, acceleration
Velocity
Rate of change of displacement.
Viscous force
Frictional force exerted on an object as it moves through a fluid.
volt (V)
Definition: The p.d. between two points is 1 V when 1 C of charge moves between those points and 1 J of energy is transferred.
V = W/Q
Wavelength
Distance between two consecutive crests
or
Distance between two consecutive troughs.
Weight
Gravitational force acting on a mass.
Work
Product of force and distance moved in the direction of force.
W = F x d
Work done by an expanding gas
Work done = pressure x change in volume
In a p-V graph, work done is the area under the graph.
Work done in stretching a spring
W = ½ Fe = ½ ke^2
In a F-e graph, work done = area under graph.
Young double slit
wavelength = ax/D
Young modulus
Ratio of stress to strain.
E = stress/strain
Newton’s 1st law of motion
A body at rest will remain at rest and a moving body will continue moving in a straight line with constant speed, unless an external resultant force acts on it.
Newton’s 2nd law of motion
The resultant force is equal to the rate of change of momentum.
Newton’s 3rd law of motion
If body A exerts a force on body B, then body B exerts an equal force on body A in the opposite direction. The forces are of the same type.
Principle of conservation of momentum
The total momentum of a system before a collision equals to the total momentum after collision, provided that no external force acts on the system.
Principle of moments
The sum of clockwise moments about any point is equal to the sum of anti-clockwise moments for a body in equilibrium.
Hooke’s Law
Force is proportional to extension, provided that the limit of proportionality has not been exceeded.
Principle of superposition
When two or more waves meet, the resultant displacement is the vector sum of the individual displacements of the waves.
Ohm’s law
The current passing through a conductor is proportional to the potential difference across it, provided that its temperature remains constant.
Kirchhoff’s 1st law
The sum of currents entering a point in a circuit is equal to the sum of currents leaving the point.
Kirchhoff’s 2nd law
The sum of e.m.f.s in a closed circuit is equal to the sum of potential differences.
Doppler effect
The change in the observed frequency when the source is moving relative to the observer.
Strong nuclear force
The force that holds the nucleus together. It acts over very short distances (10-14 m).
Hadrons
Particles that are affected by the strong nuclear force. Examples: protons and neutrons.
There are 2 types of hadron:
Baryons
Mesons
Leptons
Particles that are NOT affected by the strong nuclear force.
Examples: electrons, neutrinos, positrons and antineutrinos.
Types of quark
up (u)
down (d)
strange (s)
Baryons
Particles that are made up of 3 quarks.
Examples: protons and neutrons.
Fundamental particles
Particles that do not appear to be composed of any smaller particles.
Examples: quarks and leptons
