OCR A A-Level Physics Paper 2

Describe how ultrasound scanning is used to obtain diagnostic information about internal

structures of a body.

-Pulses of ultrasound (sent into the body)

-Wave / ultrasound / pulse / signal is reflected (at boundary of tissue)

-Time of delay used to determine depth / thickness

-The fraction of reflected signal is used to identify the

tissue

Describe the piezoelectric effect

The application of a p.d. across a material / crystal causes

an expansion / contraction / vibration

Describe the differences between an A-scan and a

B-scan

-A-scan in one direction only / range or distance or depth

finding

-B-scan uses a number of sensors or a sensor in different

positions / angles (to build up a 2D/3D image)

Alpha-particle scattering experiment is...

evidence of a small, charged nucleus

Simple nuclear model of the atom...

the atom is mostly space with a very small, very dense positively charged nucleus and negatively charged electrons located in the atomic space.

The relative size of the nucleus of an atom is...

10^-15 (metres)

The relative size of an alpha particle is...

10^-10 (metres)

The strong nuclear force...

acts between all nucleons. It is a short range force, effective over a few femtometres. Attractive above (approx.) 3fm and repulsive below (approx.) 0.5fm.

Radius of a nucleus

R = r0 A^(1/3), in which r0 is a constant and A is the nucleon number

Rutherford Gold Foil Experiment Procedure

Pointed a beam of alpha particles at a thin foil of metal and measured the scattering pattern by using a fluorescent screen.

Rutherford Gold Foil Experiment Findings

1. They spotted alpha particles bouncing off the metal foil in all directions, some right back at the source.

2. Only very few were deflected by large amounts (>90 degrees)

Rutherford Gold Foil Experiment Conclusions

1. The atom's positive charge was concentrated in a much tinier volume than Thomson imagined.

2. Tiny spheres of intense positive charge were separated by vast gulfs of empty space.

X-ray

Electromagnetic radiation with wavelength ranging from 0.1 to 10 nanometres

x-ray tube

A piece of equipment that produces x ray photons by firing electrons from a beta cathode across a large PD in an evacuated tube-x ray photons are produced when the electrons are decelerated by hitting the target metal of the anode.

Thermionic emission

The release of electrons from the surface of a heated material

Attenuation

The decrease of intensity of electromagnetic radiation as it passes through matter and/or space

Attenuation coefficient

A measure of the absorption of x-ray photons by a substance. Also called absorption coefficient

CAT scan

Computer Axial Tomography; x-ray images taken in a ring around the body to produce a composite 2d image

Medical tracer

A compound labelled with a radioisotope that can be traced inside the body with a gamma camera

Collimator

Part of a gamma camera, a honeycomb of long thin tubes made from lead that absorbs any photons arriving at an angle to the axis of the tubes so that a clear picture is obtained

Scintillator

Part of a gamma camera, that produces thousands of visible photons when struck by a single gamma photon

Photomultiplier tube

A piece of equipment that converts a photon of visible light into an electrical pulse

PET scan

Positron emission tomography scan; forms an image from the 2 gamma rays produced during the annihilation of a positron and an electron

Ultrasound

Sound that is higher frequency than the typical limit of human hearing (20kHz)

Ultrasound transducer

A device used both to generate and to receive ultrasound which changes electrical energy into sound and sound into electrical energy

Piezoelectric effect

When electric charge accumulates in a solid material due to an applied mechanical stress, producing a potential difference

Acoustic impedance

The product of the density and the speed of ultrasound in a substance

Intensity reflection coefficient

The ratio of reflected intensity to incident intensity at a boundary

Coupling gel

A gel with acoustic impedance similar to that of skin smeared onto the transducer and the patient's skin before an ultrasounds scan in order to fill air gaps and ensure that almost all the ultrasound enters the patient's body

Impedance matching

The use of two substances with similar acoustic impedance to minimise reflection of sound waves at the boundary

Annihilation

The complete destruction of a particle and its anti particle in an interaction that releases energy in the form of identical photons

Rest mass

The mass of a particle at rest

Binding energy

The energy required to dissemble the nucleus of a particular isotope into its fundamental nucleons

Mass defect

The difference in mass between a nucleus and its separated nucleons

Binding energy per nucleon

The binding energy divided by the number of nucleons in the nucleus of an isotope

Nuclear fission

A process in which a large nucleus splits into two smaller nuclei and two or three fast moving neutrons

Induced fission

Fission caused by the absorption of another particle

Nuclear fusion

A process in which two smaller nuclei join together to form one larger nucleus

Thermal neutron

A neutron with the same amount of kinetic energy as the thermal energy of its surroundings - used to initiate fission reactions

Chain reaction

A self propagating reaction - the products from one event are able to initiate the next

Coolant

A fluid of a high specific heat capacity used to transfer heat from reaction chamber to the boiler

Control rod

Absorbs excess neutrons in fission reaction to prevent/slow chain reaction in reactor core

Moderator

Material in a nuclear reactor used to slow down rapidly moving neutrons enough so that they are able to initiate fission

Beta decay

A process where a proton turns into a neutron and releases a high energy electron and an antineutrino, or where a neutron turns into a proton and releases a high energy positron and a neutrino

Ionising radiation

Radiation that can ionise atoms by removing some of their electrons, leaving positive ions

Radioactivity

The process by which unstable nuclei split or decay emitting ionising radiation (alpha, beta and gamma)

Cloud chamber

A detector of ionising radiation consisting of a chamber filled with air, saturated with vapour at a very low temperature so that droplets of liquid condense around ionised particles left along the path of radiation

Alpha radiation

Ionising radiation consisting of particles comprised of two protons and two neutrons

Beta radiation

Ionising radiation consisting of fast moving electrons or positrons

Gamma radiation

Ionising radiation consisting of high energy photons with wavelengths less than 10-13m which travel at the speed of light

Parent nucleus

A nucleus before the occurrence of radioactive decay

Daughter nucleus

A new nucleus formed following a radioactive decay

Half-life

The time taken for half a sample of material to decay, or for the activity to decrease to half its original value

Activity

Rate of decay

Decay constant

The probability of decay of an individual nucleus per unit time

Carbon-dating

A method for determining the age of organic material, by comparing the activities, or the ratios, of carbon 14 to carbon 12 nuclei of dead material of interest and similar living material

Nucleus

Centre of an atom which is made up of neutrons and protons

Nucleon

A proton or a neutron

Nucleon number

The total number of protons and neutrons in the nucleus of an atom

Proton number

The number of protons in the nucleus of an atom

Isotopes

Isotopes are nuclei of the same element that have the same number of protons but different numbers of neutrons

Atomic mass unit

One atomic unit is one-twelfth the mass of a neutral carbon-12 atom

Strong nuclear force

One of the four fundamental forces in nature, acting on hadrons and holding nuclei together

Weak nuclear force

One of the four fundamental forces in nature, acting on hadrons and leptons, responsible for inducing beta-decay.

Antiparticle

A particle with the same mass but opposite charge of another

Positron

Anti electron (charge of +1e)

Fundamental particle

A particle that has no internal structure and hence cannot be divided into smaller particles

Hadron

A particle made up of quarks and which can take part in strong force interactions

Lepton

Particles and antiparticles that do not experience the strong force. Including electrons, neutrinos and muons.

Quark

An elementary particle that can exist in six flavours, plus their antiparticles and joins with other quarks to make hadrons

Meson

Hadrons made with a combination of a quark and an anti-quark

Baryon

Hadrons made with a combination of three quarks or three anti-quarks

Standard model

The current theory of particle physics, where the elementary particles consists of six quarks, six leptons, their antiparticles, and bosons for each of the four fundamental forces

Magnetic field

The region of space in which a current or moving charge will experience a perpendicular magnetic force

Right hand screw rule

A rule used determine the direction of the magnetic field lines that surround a current-carrying wire

Flemming's left hand rule

A rule used determine the direction of the force acting on a current-carrying wire in a magnetic field:

Thumb = force, First Finger= field(magnetic), second finger= current

Magnetic flux density

The strength of a magnetic field, defined by F/IL, F = force, I = current L= length

Magnetic flux

The product of the component of the magnetic flux density perpendicular to a given area and that cross-sectional area

Magnetic flux linkage

The product of the number of turns in a coil N, and the magnetic flux φ

Faraday's law

The EMF induced by a changing magnetic field is directly proportional to the rate of change of magnetic flux linkage

Lenz's law

The direction of the induced EMF or current is always such as to oppose the change producing it

Point charge

An electric charge considered to exist at a single point, and thus having no volume

Positive charge

One type of electric charge - positively charged objects attract negatively charged ones, and repel other positive charges

Negative charge

One type of electric charge - negatively charged objects attract positively charged ones, and repel other negative charges

Electric field

A region where a charged particle will experience an electric force

Electric field strength

The force experienced per unit positive charge at that point

Radial Field

A symmetrical field that diminishes with distance squared from its centre, such as the electrical field around a spherical charged object

Coulomb's Law

Any two point charges exert an electrostatic (electrical) force on each other that is directly proportional to the product of their charges and inversely proportional to the square of their separation

Electric Potential

The work done by an external force per unit positive charge to bring a charge from infinity to a point in an electrical field

Electric Potential Difference

The work done by an external force per unit positive charge to move a charge between two points in an electrical field

Similarities to Gravitational Fields

Both are radial fields, both follow an inverse square law

Differences to Gravitational Fields

Gravitational fields are only attractive, electrical fields can be attractive and repulsive.

Capacitance

The charge stored per unit potential difference across a capacitor

Capacitor

A component that stores charge, consisting of two plates separated by an insulator (dielectric)

Farad

Unit for capacitance equivalent to CV-1. 1F is 1C of charge stored per volt.

Time constant

The product of capacitance and resistance, CR, for a capacitor-resistor circuit - equal to the time taken for the p.d. (or the current, or the charge) to decrease to e-1 (about 37%) of its initial value when the capacitor discharges through a resistor - symbol τ (tau), measured in seconds

Exponential decay

A constant-ratio process in which a quantity decreases by the same factor in equal time intervals (fixed time intervals)

Conservation of charge

A conservation law that states that electric charge cannot be created nor destroyed - total charge in any interaction must be the same before and after the interaction

Law of capacitors in series

1/C = 1/C1 + 1/C2 + ....