# WJEC Definitions and Answers A2

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WJEC Definitions (A2) Items in bold italic can be defined using equation PH4 Item Definition from memory Definition from notes / textbook Period T for a point describing a circle Frequency f

Equation relating T and f Centripetal force (in words) Centripetal acceleration Centripetal force

Angular velocity . Simple harmonic motion (shm) Simple harmonic motion (shm) (Alternative definition) Period T for an oscillating body Amplitude A of an oscillating object Equations relating position,

velocity and acceleration with time in SHM Item Phase Definition from memory Definition from notes / textbook

Free oscillations [Natural oscillations] Damping

Critical damping Forced oscillations Resonance

Momentum

Newtons laws of motion: 1st law Newtons laws of motion: 2nd law Newtons laws of motion: 3rd law The principle of conservation of momentum Elastic collision.

Item Inelastic collision.

Definition from memory

Definition from notes / textbook

Boyles law

Charles Law

Pressure Law

Ideal gas

The mole

Avogadro constant NA Internal energy, U, of a system Heat, Q

Work, W

Temperature

Item Average kinetic energy of molecules Pressure of gas (in terms of molecular properties) First law of thermodynamic s Specific heat capacity c. Electric field strength E (definition) Electric field strength (uniform field only) Electric field strength around a point charge (spherical field) Coulombs Law Gravitational field strength g. Gravitational field strength around a point mass (spherical field) Newtons law of gravitation.

Definition from memory

Definition from notes / textbook

Electric potential VE. (words and equation for uniform field)

Item Electric potential at a point in a spherical field Gravitational potential Vg (words and equation for uniform field) Gravitational potential at a point in a spherical field Keplers laws of planetary motion: 1 Keplers laws of planetary motion: 2 Keplers laws of planetary motion: 3 Keplers third law in terms of circular motion and Newtons Law of Gravitation (derivation) Dark matter

Definition from memory

Definition from notes / textbook

Radial velocity of a star [in the context of Doppler shift]

PH5 Item Capacitor Definition from memory Definition from notes / textbook

Capacitance, C, of a capacitor 1 Farad

Capacitors in series Capacitors in parallel Energy stored on a capacitor Capacitance (in terms of design of capacitor) What is an exponential decay? Decay of I (or V or Q) with time as capacitor discharges Time constant

Dielectric

Magnetic field strength, B (Magnetic flux density)

Item 1 Tesla

Definition from memory

Definition from notes / textbook

Force on a moving charge in a magnetic field Radius of orbit, r of charged particle, mass m and charge q, moving in a circle at speed v in magnetic field B Field strength of a long straight wire Field strength of a solenoid Hall voltage

Ampre A

Magnetic flux . 1 Weber

Flux linkage N Faradays law

Item Lenzs Law.

Definition from memory

Definition from notes / textbook

Root-meansquare (rms) value Alpha () radiation Beta () radiation Gamma () radiationA Z

X notation

Half life T1 of a 2 nuclide Activity A

1 Bequerel

Decay constant (in words) Decay constant in terms of half life

Item Radioactive decay equation(s)

Definition from memory

Definition from notes / textbook

Radio-isotopes

Unified atomic mass unit u. Electron volt (eV). Binding energy of a nucleus. Conservation of massenergy Nuclear fission

Chain reaction

Option C Item Crystal

Definition from memory

Definition from notes / textbook

Crystalline solid Amorphous solid Polymeric solid Hookes Law for rods and wires Stress

Strain

The Young Modulus Ductile material Elastic strain Plastic (or inelastic) strain Elastic limit

Item Dislocation s in crystals Grain boundaries Ductile fracture (necking) Creep Fatigue failure Workhardening (cold working) Annealing

Definition from memory

Definition from notes / textbook

Quenchhardening Brittle material Brittle fracture Thermoplas tic polymers Thermosett ing polymers Elastic hysteresis A2 Definitions (WJEC) Answers

PH4 Item Period T for a point describing a circle Frequency f Definition

Time taken for one complete circuit.

The number of circuits or cycles per second.

Eqn relating f and T

T = 1/f

Centripetal force

The description of an unbalanced force that causes a body to move in a circle. The direction of the force is at right angles to the velocity of the body.

Centripetal acceleration Centripetal force Angular velocity . Simple harmonic motion (shm) Simple harmonic motion (shm) (Alternative definition) Period T for an oscillating body Amplitude A of an oscillating object

a = v2 / r, or 2r or V

F = mv2 / r For a point describing a circle at uniform speed, the angular velocity is equal to the angle swept out by the radius in time t divided by t . ( = / t) UNIT: [rad] s-1 Shm occurs when an object moves such that its acceleration is always directed toward a fixed point and proportional to its distance from the fixed point. (a = 2x) The motion of a point whose displacement x changes with time t according to x = A sin ( t +), where A, and are constants. [Variations of this kind are said to be sinusoidal.]

The time taken for one complete cycle. The maximum value of the objects displacement (from its equilibrium position). x = A sin(2 f t + ) or x = A sin( t + ) v = A cos ( t + ) a = - A 2sin ( t + ) or a = - 2 x The phase of an oscillation is the angle ( t + ) in the equation x = A sin ( t + ). [ is called the phase constant.] UNIT: rad

Equation relating position, velocity and accel and time for SHMPhase

Item

Definition

Free oscillations [Natural oscillations]

Free oscillations occur when an oscillatory system (such as a mass on a spring, or a pendulum) is displaced and released.[The frequency of the free oscillations is called the systems natural frequency.] Damping is the dying away, due to resistive forces, of the amplitude of free oscillations. Critical damping is the case when the resistive forces on the system are just large enough to prevent oscillations occurring at all when the system is displaced and released. These occur when a sinusoidally varying driving force is applied to an oscillatory system, causing it to oscillate with the frequency of the applied force. If, in forced vibrations, the frequency of the applied force is equal to the natural frequency of the system (e.g. mass on spring), the amplitude of the resulting oscillations is large. This is resonance. The momentum of an object is its mass multiplied by its velocity. (p = mv). It is a vector. UNIT: kg m s-1 An object continues moving at constant speed in a straight line, or remains at rest, unless acted upon by a resultant force. The rate of change of momentum of an object is proportional to the resultant force acting on it, and takes place in the direction of that force. If a body A exerts a force on a body B, then B exerts an equal and opposite force on A. The vector sum of the momenta of bodies in a system stays constant even if forces act between the bodies, provided there are no forces from outside the system. A collision in which there is no change in total kinetic energy.

Damping

Critical damping

Forced oscillations

Resonance

Momentum Newtons laws of motion: 1st law Newtons laws of motion: 2nd law Newtons laws of motion: 3rd law The principle of conservation of momentum Elastic collision.

Inelastic collision.

A collision in which kinetic energy is lost. For a fixed mass of gas at constant temperature [unless its density is very high], the pressure varies inversely as the volume. pV = k For a fixed mass of gas at constant pressure, the temperature is directly proportional to the volume. V/T = k

Boyles law

Charles Law

Item

Definition For a fixed mass of gas at constant volume, the pressure is directly proportional to the temperature. P/T = k An ideal gas strictly obeys the equation of state pV = nRT, in which n is the number of moles, T is the kelvin temperature and R is the molar gas constant. R = 8.31 J mol-1K-1. Except at very high densities a real gas approximates well to an ideal gas. The mole is the S.I. unit of amount of substance, n. It is the amount containing as many particles (e.g. molecules) as there are atoms in 12 g of carbon12. This is the number of particles per mole. (NA=6.02 1023 mol-1). This is the sum of the kinetic and potential energies of the particles of the system. This is energy flow from a region at higher temperature to a region at lower temperature, due to the temperature difference. In thermodynamics we deal with heat going into or out of a system. It makes no sense to speak of heat in a system. If the system is a gas, in a cylinder fitted with a piston, the gas does work of amount pV when it exerts a pressure p and pushes the piston out a small way, so the gas volume increases by V. Work, like heat, is energy in transit from (or to) the system. Average k.e. of particles The root mean square speed (ie the square root of the mean of the velocity of all the particles squared). The mean square speed (referred to as 2 or 2) can be calculated using either of the expressions below. m 2 = 3/2 kT (k = Bolzmann constant)

Pressure Law

Ideal gas

The mole Avogadro constant NA Internal energy, U, of a system

Heat

Work