Paper 4 definitions

Angular velocity

angular displacement per unit time

Field line

Represents the path a mass would take when placed within the field

Gravitational field

Area where object with mass experiences an attractive force due to gravity

Gravitational potential

Work done in moving a unit mass from an infinite distance to that point

Newton’s law of gravitation

Force between two masses is proportional to the product of the masses involved and inversely proportional to the square of the separation of the masses

Synchronous orbit

An orbit with a time period of one day. Orbiting body will return to the same point in the sky each day

Specific heat capacity

Amount of energy required to increase the temperature of 1kg of a substance by 1 Kelvin without changing state

Specific latent heat

amount of energy required to change the state of a substance per kg without a change of temperature.

Fusion - solid to liquid

Vaporisation - liquid to gas

Internal energy

Sum of randomly distributed potential and kinetic energies of the particles in a substance.

(In an ideal gas, will just be the KE as we assume there to be no intermolecular forces so no potential energy between particles).

Critical damping

Damping that reduces displacement of an oscillating object to its equilibrium position in the quickest time possible, without further oscillation.

Damping

Occurs when a force opposes the system’s motion. Energy is dissipated from the oscillating system.

Natural frequency

a system naturally oscillates at this when there is no external force applied.

Overdamping

System is damped more than required to stop oscillations. It takes longer for the system to return to equilibrium than for critical damping

Simple Harmonic Motion

Acceleration is directly proportional to the acceleration of the object in the opposition direction

Underdamping

A type of damping where energy is gradually removed from the system. Amplitude slowly decreases.

Coulomb’s law

force that acts between two point charges is proportional to the product of their charges and inversely proportional to the square of their separation.

Attractive for opposite charges and repulsive for like charges.

Electric field strength

Force per unit positive charge

Electric potential

Work done per unit charge on a positive test charge in bringing it from infinity to a point in the field

Equipotential

Surface of constant potential. No work is done by the field when an object moves along an equipotential

Electric field lines

Lines demonstrating direction which a positive charge would follow

Capacitance

Charge stored per unit pd in a capacitor

What is a parallel plate capacitor

Two parallel conducting plates. With an insulator between them (dielectric)

Electromagnetic induction

An emf is induced in a wire when it is moved relative to a magnetic field

Faraday’s law

Induced E.M.F in a circuit is proportional to the rate of change of magnetic flux linkage through the circuit and acts in a direction that opposes the change producing it.

Lenz’s law

direction of an induced current is such that it opposes the current that created it

Magnetic flux density

Force per unit current per unit length on a current carrying wire placed perpendicular to the field. Measured in Tesla.

De Broglie hypothess

All particles have a wave-like natue and a particle-like nature.

Wavelength = h/momentum.

Intensity

Power transferred per unit area

Emission spectrum

When atom’s de-excite they move from one energy level to another, with a discrete energy gap between these levels. This creates a photon of that energy and the frequency of this photon make up the emission spectrum.

Absorption spectrum

Frequencies at which an element absorbs photons corresponds to the spacings between energy levels in the element’s atoms.

Photon

A discrete quanta of energy of electromagnetic radiation. E=hf.

Threshold frequency

Minimum frequency of light needed to cause electrons to be emitted from the surface of a metal. (Sometimes energy required will be higher than threshold as energy needed to get electrons to surface).

Can also be thought of as MAX wavelength.

Work function

Minimum energy required to remove an electron from a metal’s surface.

Activity

rate of decay of radioactive nuclei in an isotope.

(A = N x decay constant)

Measured in Becquerels

Binding energy

Energy required to split a nucleus into its individual nucleons to infinity.

(The greater the binding energy per nucleon, the more stable the nucleus is).

Decay constant

Constant probability of a nuclear decay occurring per unit time

Mass-energy equivalence

The energy equivalent of a given mass is equal to the product of the mass and the speed of light squared

Mass defect

Difference in mass between a nucleus and the sum of the masses of its constituent nucleons

Random nature of decay

Cannot predict when a nucleus will decay

Spontaneous nature of decay

Decay is independent of physical factors such as temperature

Acoustic impedance

Product of the speed of sound through a given medium and the density of the medium

Attenuation of X-Rays

Reduction of the intensity of X-rays when they pass through matter. Decay of this intensity is exponential.

Briefly outline Computerised Axial Tomography Scanning

• produces a cross section of the body by rotating a monochromatic x-ray beam around it in combination with a series of detectors

How do piezoelectric crystals work

When a potential difference is applied, crystals deform. When the crystal is deformed, a potential difference is produced

What type of wave is ultrasound, and what frequency do they sit above

They are sound waves. Higher than audible frequency (20,000 Hz)

Hubble’s law

Speed of a galaxy moving away from ours is proportional to its distance away from us.

Constant of proportionality is Hubble’s constant.

Luminosity

Total power radiated by a star.

Given by Stefan-Botlzmann Law: L = 4 x pi x R² x sigma x T⁴

What is red shift

Shifting of an object’s wavelength towards the longer wavelength end of the spectrum due to the object moving away from the Earth. Doppler effect. Red shift is evidence for the expansion of the universe.

Standard candle

Object of known luminosity, used as a reference to measure other stars and the distance to them.

Wien’s displacement law

The peak wavelength of emitted radiation is inversely proportional to its absolute temperature.

wavelength x T = constant.

State the order of the electromagnetic spectrum from largest wavelength to smallest.

Radio

Microwave

Infrared

Visible (ROYGBIV)

Ultraviolet

X-Ray

Gamma Ray