paper 2 physics Flashcards
State
what is meant by the
decay constant
of an isotope
The decay constant is the probability of decay of a
nucleus
per unit time
State
what is meant by
induced
nuclear fission
.
The splitting of a (uranium) nucleus
as a neutron is absorbed
Explain the role of the moderator and the control rods in a nuclear reactor.
the moderator slows down fast moving neutrons
he neutrons lose significant amount of their kinetic energy when colliding with moderator nuclei
. the control rods absorb neutrons
rate of fission is reduced
Describe the X-ray attenuation mechanisms of simple scatter and
pair production
Simple scatter: X-ray(photon) is scattered by an atomic electron
Pair production: An X-ray (photon) transforms into an electron and positron pair.
State what is meant by the piezoelectric effect
The material expands or contracts when a p.d. is applied across its
opposite faces
Describe and explain a method using ultrasound to
determine the spe
ed of blood in an artery in an
arm.
State one major advantage of this technique for the patient
The transducer is placed at an angle to the arm or artery and ultrasound is reflected by the moving blood cells. The wavelength or the frequency of the reflected ultrasound is altered. Since, the change in frequency proportional to speed of the blood. The technique is non-invasive/no incision needed/minimises risk of infection.
what is the wavelength of an electron when diffracted
The electrons have a wavelength of about 10^–10 m
model of electromagnetic waves.
Discuss how the new knowledge of the
particulate nature of radiation
was used by physicists to
validate the photon model
The wave model cannot explain why there is a threshold frequencyfor metals. The new model proposed one-to-one interaction between photons and electrons and this successfully explained why threshold frequency exists .Energy of photon (hf) must be greater than or equal to work function of metal
Describe
how the time constant of this circuit can be determined
experimentally in the laboratory
Connect a voltmeter or data-logger or oscilloscope across the resistor(or capacitor) or an ammeter in series with the resistor .A stopwatch is started when the switch is opened and stopped when the p.d. or the current to decreases to 37% of its initial value. The time constant is the time taken for the p.d . or the current to decreases to 37% of its initial value
Describe how the components of a computerised axial tomography (CAT) scanner can
produce high-quality images of the internal structures of a patient.
X-ray (tube) moves around the patient A thin (fan-shaped X-ray) beam is used(Images / scans of) cross-sections through the patient are taken
A 3 dimensional image is produced
Which lepton is emitted in the decay of an up quark and is affected by a magnetic field?
positron
Describe how you can demonstrate in the laboratory that the reflected light is plane polarised
use a polaroid / polarising filter
Rotation will change intensity
