NUMS — Medical & Dental Entry Test
Take the NUMS Physics — Electronics, Modern and Nuclear Physics (Set 7): 30 multiple-choice questions (40 minutes) with instant scoring and a full answer…
What this test covers
The first 5 questions of this test, with the correct answer and explanation.
Q1. Light of wavelength 400 nm falls on a metal of work function 2.0 eV. Using hc = 1240 eV nm, what is the stopping potential?
Answer: D. 1.1 V
Explanation: Photon energy = 1240/400 = 3.10 eV; K_max = 3.10 − 2.0 = 1.1 eV; the stopping potential is 1.1 V.
Q2. The work function of a metal is 4.14 eV. What is the longest wavelength of light that can eject photoelectrons from it? (hc = 1240 eV nm)
Answer: C. 300 nm
Explanation: λ₀ = hc/φ = 1240/4.14 = 300 nm; longer wavelengths have too little energy per photon.
Q3. A helium–neon laser emits 2.0 mW of light at 632.8 nm. Approximately how many photons does it emit per second? (h = 6.626 × 10⁻³⁴ J s, c = 3.0 × 10⁸ m s⁻¹)
Answer: B. 6.4 × 10¹⁵
Explanation: E per photon = hc/λ = 3.14 × 10⁻¹⁹ J; N = 2.0 × 10⁻³/3.14 × 10⁻¹⁹ = 6.4 × 10¹⁵ per second.
Q4. In Compton scattering the shift in wavelength is Δλ = (h/m₀c)(1 − cos φ), where h/m₀c = 2.43 pm. What is the shift for a photon scattered straight back (φ = 180°)?
Answer: D. 4.85 pm
Explanation: 1 − cos 180° = 2, so Δλ = 2 × 2.43 = 4.85 pm, the maximum possible shift.
Q5. An alpha particle (m = 6.64 × 10⁻²⁷ kg) has kinetic energy 5.0 MeV (1 eV = 1.60 × 10⁻¹⁹ J). What is its de Broglie wavelength? (h = 6.63 × 10⁻³⁴ J s)
Answer: D. 6.4 fm
Explanation: p = √(2mK) = √(2 × 6.64 × 10⁻²⁷ × 8.0 × 10⁻¹³) = 1.03 × 10⁻¹⁹ kg m s⁻¹; λ = h/p = 6.4 × 10⁻¹⁵ m = 6.4 fm.
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Q6. An electron in a hydrogen atom falls from the n = 5 level to the ground state, possibly stopping at intermediate levels. What is the maximum number of different spectral lines that can be emitted?
Q7. Electrons accelerated through 40 kV strike a target in an X-ray tube. What is the minimum wavelength in the continuous X-ray spectrum? (hc = 1240 eV nm)
Q8. A radioactive sample has a half-life of 10 days. What fraction of the original nuclei remains after one mean life (τ = T½/ln 2)?
Q9. Thorium-232 (Z = 90) decays through a series to stable lead-208 (Z = 82), emitting only alpha particles and beta (β⁻) particles. How many of each are emitted?
Q10. The masses of the proton, neutron and deuteron nucleus are 1.007276 u, 1.008665 u and 2.013553 u. Taking 1 u = 931.5 MeV, what is the binding energy of the deuteron?
Q11. In the fusion reaction ²H + ³H → ⁴He + n the atomic masses are 2.014102 u, 3.016049 u, 4.002603 u and the neutron 1.008665 u. Taking 1 u = 931.5 MeV, how much energy is released?
Q12. Each fission of a uranium-235 nucleus releases about 200 MeV. How much energy is released when 1.0 kg of ²³⁵U fissions completely? (1 MeV = 1.6 × 10⁻¹³ J; Nₐ = 6.0 × 10²³ mol⁻¹)
Q13. In the decay ²²⁶Ra → ²²²Rn + ⁴He the atomic masses are 226.0254 u, 222.0176 u and 4.0026 u. Taking 1 u = 931.5 MeV, what is the total energy released (Q value)?
Q14. Carbon-14 (Z = 6) decays by β⁻ emission. Which row correctly describes the daughter nucleus and the particles emitted?
Q15. The nuclear radius is given by R = R₀A^(1/3) with R₀ = 1.2 fm. What is the radius of the nucleus of copper-64?
Q16. A silicon p–n junction is reverse biased. What is the origin of the small leakage current that still flows?
Q17. A silicon diode (forward drop 0.7 V) is connected in series with a 100 Ω resistor across a 5.0 V battery in the forward direction. What current flows?
Q18. The 220 V (rms) mains supply is fed to an ideal half-wave rectifier. What is the average value of the output voltage?
Q19. A Zener diode (breakdown voltage 6.0 V) in a regulator circuit is fed from 12 V through a 120 Ω series resistor, with a 200 Ω load connected across the diode. What current flows through the Zener diode?
Q20. A transistor with β = 50 is used as a switch to drive a 10 mA collector current from a 5.0 V input through a base resistor (V_BE = 0.7 V). What base resistor value just saturates it?
Q21. A non-inverting op-amp amplifier has a feedback resistor of 18 kΩ and a resistor of 2.0 kΩ from the inverting input to earth. What is the output voltage for an input of 0.15 V?
Q22. A circuit gives Y = (A + B)·(A·B)′, that is, (A OR B) AND NOT (A AND B). For which input combinations is Y = 1?
Q23. What is the sum of the binary numbers 1011 and 0111, written in binary?
Q24. A light-emitting diode is made from a semiconductor with a band gap of 1.9 eV. Approximately what wavelength of light does it emit? (hc = 1240 eV nm)
Q25. Silicon has a band gap of about 1.1 eV. What is the longest wavelength of light that can create electron–hole pairs in it?
Q26. A nuclear power station produces 600 MW of thermal power and each fission releases 200 MeV (1 MeV = 1.6 × 10⁻¹³ J). How many fissions occur per second?
Q27. A 70 kg worker absorbs 0.35 J of energy from alpha radiation spread uniformly through the body. If the quality factor for alpha particles is 20, what is the equivalent dose?
Q28. An electron and a positron annihilate at rest, producing two photons of equal energy. What is the wavelength of each photon? (Rest energy of an electron = 0.511 MeV; hc = 1240 eV nm)
Q29. The Balmer series limit corresponds to a transition from n = ∞ to n = 2 in hydrogen. Using R = 1.097 × 10⁷ m⁻¹, what is the wavelength of this series limit?
Q30. In Rutherford's experiment a 5.0 MeV alpha particle approaches a gold nucleus (Z = 79) head-on. Taking all its kinetic energy to become electrostatic potential energy at closest approach, what is the distance of closest approach? (k = 9.0 × 10⁹ N m² C⁻², e = 1.6 × 10⁻¹⁹ C)