OCR A A-Level Physics Paper 2
Study
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
Study
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
