Physics questions and solutions

Browse original practice and official past-paper questions. Each question has its own link, with its source and worked solution.

498 questions · Page 14 of 21

1. Q99 · Original practice · 5 marks
   At quark level, beta-minus decay can be represented by a down quark changing into an up quark and emitting a $W^-$ boson, which then produces an electron and an electron antineutrino. Explain how this converts a neutron into a proton and verify conservation of electric charge and lepton number.
   The Standard Model
2. Q100 · Original practice · 5 marks
   Consider the weak interaction $\nu_e+n\rightarrow p+e^-$. Determine the total baryon number, total electron-family lepton number and total electric charge before and after the interaction, and state whether each is conserved.
   The Standard Model
3. Q101 · Original practice · 1 mark
   During beta-minus decay, a neutron changes into a proton and an electron is emitted: $n \rightarrow p + e^- + X$. Which particle must $X$ be so that electric charge and lepton number are both conserved?
   The Standard Model
4. Q102 · Original practice · 1 mark
   A ball is launched horizontally. Air resistance is negligible. When the ball has travelled a horizontal distance of $4.0\,\mathrm{m}$, its velocity is directed $30^\circ$ below the horizontal. Take $g=9.8\,\mathrm{m\,s^{-2}}$. What was the ball's initial speed?
   Projectile motion
5. Q103 · Original practice · 6 marks
   Five satellites move in approximately circular orbits around the same planet. Their measured orbital radii and periods were processed to produce the graph. The broken line shows a proportional $T^2$-versus-$r^3$ model fitted to the data, consistent with Kepler's third law.
   Orbital mechanics
6. Q104 · Original practice · 7 marks
   An 80-turn rectangular coil of area $6.0\times10^{-3}\,\mathrm{m^2}$ moves at constant speed across a sharp boundary from a uniform $0.30\,\mathrm{T}$ field into the page into a uniform $0.20\,\mathrm{T}$ field out of the page. At $t=0$ its leading edge reaches the boundary. It takes $0.050\,\mathrm{s}$ to move fully across, and the fraction of its area on t…
   Electromagnetic induction
7. Q105 · Original practice · 8 marks
   An electron enters a uniform magnetic field $B=2.00\times10^{-3}\,\mathrm{T}$ directed into the page, with velocity perpendicular to the field. The measured circular-path radius is $2.50\times10^{-2}\,\mathrm{m}$. The speed is low enough that classical momentum $p=mv$ may be used.
   Quantum theory
8. Q106 · Original practice · 1 mark
   A cyclist rounds a level circular bend at constant speed. Which vector points towards the centre of the bend?
   Gravity and motion
9. Q107 · Original practice · 1 mark
   A satellite is moved from a circular orbit of radius $r$ to a circular orbit of radius $4r$ around the same planet. Its orbital speed becomes
   Gravity and motion
10. Q108 · Original practice · 1 mark
    Two projectiles are launched from level ground with the same speed at $25^{\circ}$ and $65^{\circ}$. Neglect air resistance. Which quantity is the same for both?
    Gravity and motion
11. Q109 · Original practice · 1 mark
    At the midpoint between two equal positive point charges, the electric field is
    Electromagnetism
12. Q110 · Original practice · 1 mark
    A straight wire carries conventional current north in a uniform magnetic field directed east. The magnetic force on the wire is
    Electromagnetism
13. Q111 · Original practice · 1 mark
    A conducting loop is pulled out of $a$ region where a magnetic field is directed into the page. While the flux into the page is decreasing, the induced field is
    Electromagnetism
14. Q112 · Original practice · 1 mark
    An ideal transformer has $600$ turns on its primary and $150$ turns on its secondary. A $240\,\mathrm{V} rms$ supply is connected to the primary. The secondary voltage is
    Electromagnetism
15. Q113 · Original practice · 1 mark
    Which electromagnetic radiation has the greatest photon energy?
    Electromagnetism
16. Q114 · Original practice · 1 mark
    The proper time between two events is measured in the frame in which the events occur
    Special relativity
17. Q115 · Original practice · 1 mark
    A spacecraft moves at relativistic speed past Earth. Earth observers measure the spacecraft length along its motion as
    Special relativity
18. Q116 · Original practice · 1 mark
    Increasing the intensity of light below a metal’s threshold frequency will
    Quantum theory
19. Q117 · Original practice · 1 mark
    If a particle’s momentum triples, its de Broglie wavelength becomes
    Quantum theory
20. Q118 · Original practice · 1 mark
    An electron in hydrogen drops from $n=4$ to $n=2$. Compared with a drop from $n=3$ to $n=2$, the emitted photon has
    Quantum theory
21. Q119 · Original practice · 1 mark
    A black-body spectrum shifts to a smaller peak wavelength when temperature increases. This is described by
    Quantum theory
22. Q120 · Original practice · 1 mark
    Which quark has electric charge $+\frac{2}{3} e$?
    The Standard Model
23. Q121 · Original practice · 1 mark
    In $\beta$-minus decay, total lepton number is conserved because the emitted electron is accompanied by
    The Standard Model
24. Q122 · Original practice · 1 mark
    An electron and positron annihilate from rest. Momentum conservation requires the final state to include at least
    The Standard Model