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 13 of 21

1. Q75 · Original practice · 4 marks
   A conducting rod moves to the right through a uniform magnetic field directed into the page. Explain why a potential difference develops between the rod’s ends and identify which end becomes positive.
   Electromagnetic induction
2. Q76 · Original practice · 4 marks
   A $250$-turn coil has area $0.015\,\text{m}^2$. Its normal is parallel to a magnetic field that decreases uniformly from $0.40\,\text{T}$ to zero in $0.12\,\text{s}$. Determine the magnitude of the induced EMF.
   Electromagnetic induction
3. Q77 · Original practice · 5 marks
   An ideal transformer has $600$ primary turns and $150$ secondary turns. The primary is connected to $240\,\text{V}$ AC and the secondary supplies a $96\,\text{W}$ load. Determine the secondary voltage, secondary current and primary current.
   Electromagnetic induction
4. Q78 · Original practice · 4 marks
   A strong magnet falls axially through a conducting copper ring. Explain why its acceleration can be less than $g$ while it approaches and leaves the ring, using Faraday’s law, Lenz’s law and conservation of energy.
   Electromagnetic induction
5. Q79 · Original practice · 6 marks
   A generator coil has $80$ turns, area $0.020\,\text{m}^2$ and rotates at $50\,\text{Hz}$ in a uniform $0.12\,\text{T}$ magnetic field. If the flux through one turn is $\Phi=BA\cos(\omega t)$, derive an expression for the induced EMF and determine its maximum magnitude.
   Electromagnetic induction
6. Q80 · Original practice · 5 marks
   A spacecraft travels at $0.80c$ from Earth to a star $12.0$ light-years away in the Earth frame. Ignore acceleration periods. Determine the travel time measured (a) on Earth and (b) by a clock on the spacecraft.
   Special relativity
7. Q81 · Original practice · 5 marks
   Muons created high in Earth’s atmosphere travel at $0.995c$. Their proper mean lifetime is $2.2\,\mu\text{s}$. Calculate the mean lifetime and mean travel distance in the Earth frame. Compare the result with a classical calculation that ignores time dilation.
   Special relativity
8. Q82 · Original practice · 4 marks
   A rod has proper length $5.00\,\text{m}$ and is measured to be $3.00\,\text{m}$ long by an observer relative to whom it is moving. Determine the rod’s speed as a fraction of $c$.
   Special relativity
9. Q83 · Original practice · 5 marks
   Two flashes occur simultaneously at the front and rear of a train according to an observer standing beside the track. The train moves to the right. Explain which flash reaches an observer at the midpoint of the train first and what this implies about simultaneity in the train frame.
   Special relativity
10. Q84 · Original practice · 4 marks
    A proton moves at $0.95c$. Determine the ratio of its relativistic momentum to its classical momentum $mv$ and explain the physical significance of this ratio.
    Special relativity
11. Q85 · Original practice · 3 marks
    A process converts $2.5\times10^{-5}\,\text{kg}$ of mass into other forms of energy. Determine the equivalent energy.
    Special relativity
12. Q86 · Original practice · 5 marks
    One twin remains on Earth while the other travels at $0.80c$ to a star $8.0$ light-years away in the Earth frame and immediately returns at the same speed. Ignore acceleration duration. Determine the elapsed time for each twin and the age difference when they reunite.
    Special relativity
13. Q87 · Original practice · 4 marks
    The graph shows classical and relativistic momentum as speed approaches $c$. Analyse the graph and explain why a massive particle cannot be accelerated to the speed of light.
    Special relativity
14. Q88 · Original practice · 3 marks
    A star has a blackbody peak wavelength of $620\,\text{nm}$. Estimate its surface temperature using Wien’s law.
    Quantum theory
15. Q89 · Original practice · 5 marks
    Light of frequency $9.0\times10^{14}\,\text{Hz}$ illuminates a metal of work function $2.30\,\text{eV}$. Determine the maximum kinetic energy of emitted photoelectrons in eV and the corresponding maximum electron speed.
    Quantum theory
16. Q90 · Original practice · 6 marks
    Photoelectric data for a metal are shown below.

    frequency ($10^{14}$ Hz)	7.0	8.0	9.0
    maximum kinetic energy (eV)	0.40	0.81	1.23

    Use the data to estimate (a) Planck’s constant in $\text{eV s}$, (b) the threshold frequency and (c) the work function.
    Quantum theory
17. Q91 · Original practice · 5 marks
    The hydrogen energy levels $n=1$ to $n=4$ are shown. Of all possible downward transitions starting from $n=4$, identify the transition that produces the longest-wavelength photon and calculate that wavelength using the energy values on the diagram.
    Quantum theory
18. Q92 · Original practice · 4 marks
    Use the Rydberg equation to determine the wavelength emitted when a hydrogen electron falls from $n=4$ to $n=2$.
    Quantum theory
19. Q93 · Original practice · 3 marks
    A proton moves at $4.0\times10^5\,\text{m s}^{-1}$. Determine its de Broglie wavelength.
    Quantum theory
20. Q94 · Original practice · 5 marks
    Contrast Rutherford’s and Bohr’s atomic models, and explain why Bohr’s model can account for discrete hydrogen emission lines whereas Rutherford’s model cannot.
    Quantum theory
21. Q95 · Original practice · 6 marks
    A star can be approximated as a blackbody with peak wavelength $480\,\text{nm}$. A metal surface has work function $2.70\,\text{eV}$. Determine (a) the star’s approximate surface temperature, (b) the energy in eV of a photon at the peak wavelength and (c) whether a peak-wavelength photon can eject an electron from the metal.
    Quantum theory
22. Q96 · Original practice · 5 marks
    For each particle below, state whether it is a baryon or meson and determine its baryon number: (a) proton $uud$, (b) neutron $udd$, (c) $\pi^+$ meson $u\bar d$.
    The Standard Model
23. Q97 · Original practice · 3 marks
    Consider the interaction $p+\bar p\rightarrow\pi^++\pi^-$. Show that baryon number and electric charge are conserved.
    The Standard Model
24. Q98 · Original practice · 4 marks
    The diagram shows $e^-+e^+\rightarrow\mu^-+\mu^+$ through an intermediate photon. Identify the interaction responsible and show that total lepton number is conserved.
    The Standard Model