paper Flashcards
Deduce which particle, π+ or Y, has the greater charge-to-mass ratio.
Justify your conclusion.
Y has a greater rest energy than a pion / Y has greater mass than a pion ✔
Y is a kaon ✔
Pion has greater specific charge because it has the same charge as Y but less mass than Y ✔
Accept for mp2:
Y contains an s quark which is more massive than u or d quarks in the pion / Pion is 1st generation while Y is 2nd generation
Error carried forward for charge on Y from (a) Y will have a greater specific charge where Y has charge greater than +4
A sample of bromine gas contains a mixture of two isotopes. An experiment is done to find the percentage of each isotope in this sample.
(a) In the experiment, the gas is ionised by a beam of electrons.
Explain how the beam of electrons causes a particle of the gas to have a charge of +1e.
An electron in the beam collides with an electron in the gas particle.
OR
An electron in the beam transfers (some of its) kinetic energy to an electron in the gas particle ✔
This (collision) knocks one (atomic) electron out of the gas particle. ✔
Alternative MP2:
The electrons in the beam have energy greater than the ionisation energy of the gas particle
An isolated metal plate is given a negative charge. Electromagnetic radiation is incident on the plate. The plate loses its charge due to the photoelectric effect.
(a) Discuss how the rate of loss of charge from the plate depends on the frequency and intensity of the incident radiation.
In your answer you should explain why:
* the plate loses its charge
* the photoelectric effect occurs only for frequencies greater than a particular value
* the rate of loss of charge increases with intensity for radiation above that particular value of frequency.
Area A
PEE:
* Is a surface phenomenon.
* Emission of electrons (from a surface) when electromagnetic radiation is incident (on surface).
Area B
Frequency:
* Minimum energy required (work function) to release an electron from the metal surface.
* A photon must supply this energy in one interaction.
* The energy of a photon is directly proportional to its frequency.
Area C
Intensity:
* Increased intensity (at same frequency) results in more photons per second incident on metal.
* Must increase the number of photons (per second) even if frequency increases.
* More electrons released from surface every second so loses charge more rapidly.
A mobile phone transmits data to the loudspeaker using microwaves. The data are processed at the loudspeaker to produce sound waves.
Microwaves and sound waves travel at different speeds.
Describe two other differences between microwaves and sound waves.
Microwaves have higher frequency than sound;
Microwaves can be polarised but sound can’t;
Microwaves can travel through a vacuum but sound can’t OR
sound are mechanical waves but microwaves aren’t;
Microwaves are transverse; sound are longitudinal
A second loudspeaker receives the same data from the mobile phone. The two loudspeakers act as coherent sources of sound waves.
State the two conditions required for the sources to be coherent.
fixed/constant phase difference ✔
same frequency/wavelength ✔
An isolated solid conducting sphere is initially uncharged.
Electrons are then transferred to the sphere.
(a) State and explain the location of the excess electrons.
Electrons (being negatively charged) mutually repel ✔ owtte
The electrons move onto the outer surface ✔ owtte
A polonium-210 nucleus is formed when a stationary nucleus of bismuth-210 decays. A beta-minus (β−) particle is emitted in this decay.
Outline, with reference to β− decay, why bismuth-210 and polonium-210 have different proton numbers.
A neutron decays into a proton
Or
Allow a neutron changes to a proton. (owtte) Accept the decay equation of a neutron / bismuth
- Statement that neutron converts to proton✔
- all numbers correct and context ✔
Proton number increases by one when Bi-210 decays and describes beta minus
Condone missing (or incorrect) neutrino or symbol for bismuth
OR
Bi-210 has one fewer proton (than Po-210) and describes beta minus in words
OR
Po-210 has one more proton (than Bi-210) and describes beta minus in words
Or
Proton number increases from 83 to 84 and describes beta minus in words ✔
Optical fibres are used to carry pulses of light.
(a) Explain what is meant by modal dispersion in an optical fibre.
Spreading of pulse / parts of a pulse take different times to travel through the fibre / pulse broadening✔
Do not credit material dispersion.
owtte
Due to different paths through the optical fibre / due to entering the optical fibre at different angles ✔
(d) Two pulses of monochromatic light are incident normally on the air−core boundary. They then travel along the central axis of the core.
One pulse consists of blue light; the other consists of red light.
Explain, with reference to refractive index, why the pulse of red light has a shorter transit time than the pulse of blue light.
The refractive index of core for blue light is greater than the refractive index for red / The refractive index of core for red light is less than the refractive index for blue✔
Max 1 mark for stating that the refractive indices are different because their speeds are different
MP1 can come from graph or prior knowledge
The speed of the blue light is less than the speed of the red light and travel the same distance / The speed of the red light is greater than the speed of the blue light and travel the same distance✔
Another two pulses, identical to the pulses in part (d), are incident on the central axis of the optical fibre and travel along its length.
However, the pulse of red light and pulse of blue light are now incident on the air−core boundary at an angle of incidence of 30°.
Suggest one reason why the difference in their transit times may not be the same as in part (d).
he blue now travels a shorter distance than the red light (compared to (d))✔
or
the red light now travels a greater distance than the blue light (compared to (d))✔
or
the difference between the blue’s velocity parallel to the central axis and the red’s velocity (parallel to the central axis) has decreased (compared to (d)).✔
Allow: now travel different distances whereas previously travelled the same distance.
or
the difference between the horizontal velocity of the red light and the horizontal velocity of the blue light has decreased (compared to (d)).✔
1
The student has paint that fluoresces when light of any wavelength is incident on it. She coats the blue LED and the red LED with the paint.
Compare the wavelengths of light emitted by the paint on each LED.
In your answer you should also explain the processes that cause the paint to fluoresce.
Area A - Wavelength comparison:
- Red LED will emit longer wavelengths than 660 nm (accept “longer than red light).
- Blue LED will emit wavelengths longer than 440 nm (accept “longer than blue light).
- Blue LED will emit visible light. Accept named colours.
Area B - Excitation process:
- Excitation mentioned (as first step of fluoresence)
- Photons are absorbed by atoms in coating
- Atoms are excited/gain energy;
- Atomic electrons move to higher energy levels (than n = 2)
- Photons have sufficient energy to promote electrons to high enough levels
Area C - De-excitation process:
- De-excitation or relaxation mentioned (as subsequent step)
- Photons are emitted by atoms in coating
- Atoms de-excite/lose energy
- Atomic electrons move to lower energy levels
- Electrons move to ground state via other energy levels
- Emitted radiation consists of (a range of) lower photon energies/frequencies or longer wavelengths
6
(a) State what is meant by an inertial frame of reference.
One which moves at constant velocity
Allow: a reference frame in which Newton’s laws / Newton’s first law holds.
Under certain circumstances, a photon moving through a material can interact with the nucleus of an atom of the material to produce an electron and a positron.
(i) What is the name of this process?
(ii) Give one reason why the photon could not produce a single electron instead of an electron and a positron.
(i) pair production (1)
1
(ii) conservation law stated (charge or lepton number) (1)
shown to be true eg lepton number +1–1 = 0 (1)
