NUMS — Medical & Dental Entry Test

NUMS Physics — Electronics, Modern and Nuclear Physics (Set 3)

Take the NUMS Physics — Electronics, Modern and Nuclear Physics (Set 3): 30 multiple-choice questions (40 minutes) with instant scoring and a full answer…

What this test covers

30 NUMS Physics

Sample questions with answers

The first 5 questions of this test, with the correct answer and explanation.

Q1. What is the energy in electron-volts of a photon of wavelength 620 nm? (hc = 1240 eV nm)
- A. 4.0 eV
- B. 2.0 eV ✓
- C. 1.0 eV
- D. 0.50 eV
Answer: B. 2.0 eV
Explanation: E = hc/λ = 1240/620 = 2.0 eV.
Q2. Light of wavelength 400 nm falls on a metal of work function 2.3 eV. What is the maximum kinetic energy of the emitted photoelectrons? (hc = 1240 eV nm)
- A. 1.6 eV
- B. 5.4 eV
- C. 3.1 eV
- D. 0.8 eV ✓
Answer: D. 0.8 eV
Explanation: Photon energy = 1240/400 = 3.1 eV; K_max = 3.1 − 2.3 = 0.8 eV.
Q3. The work function of a metal is 2.07 eV. What is its threshold frequency? (h = 4.14 × 10⁻¹⁵ eV s)
- A. 5.0 × 10¹⁴ Hz ✓
- B. 2.0 × 10¹⁵ Hz
- C. 8.6 × 10¹⁴ Hz
- D. 5.0 × 10¹⁵ Hz
Answer: A. 5.0 × 10¹⁴ Hz
Explanation: f₀ = φ/h = 2.07/(4.14 × 10⁻¹⁵) = 5.0 × 10¹⁴ Hz.
Q4. In a photoelectric experiment, the intensity of the incident light (of frequency above threshold) is doubled while its frequency is unchanged. What happens?
- A. Neither the photocurrent nor the kinetic energy changes
- B. The maximum kinetic energy doubles but the photocurrent is unchanged
- C. Both the photocurrent and the maximum kinetic energy double
- D. The photocurrent doubles but the maximum kinetic energy of the electrons is unchanged ✓
Answer: D. The photocurrent doubles but the maximum kinetic energy of the electrons is unchanged
Explanation: Intensity sets the number of photons (and thus electrons per second); K_max = hf − φ depends only on frequency.
Q5. What is the de Broglie wavelength of an electron accelerated from rest through 150 V? (use λ = 12.27/√V Å, with V in volts)
- A. 1.0 Å ✓
- B. 12.3 Å
- C. 0.82 Å
- D. 0.1 Å
Answer: A. 1.0 Å
Explanation: λ = 12.27/√150 = 1.00 ≈ 1.0 Å.

The other 25 questions

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Q6. What is the Compton wavelength shift for a photon scattered through 90° by a free electron? (h = 6.626 × 10⁻³⁴ J s, m = 9.11 × 10⁻³¹ kg, c = 3.0 × 10⁸ m/s)
- A. 0.00 pm
- B. 1.21 pm
- C. 2.42 pm
- D. 4.85 pm
Q7. What is the momentum of a photon of wavelength 500 nm? (h = 6.626 × 10⁻³⁴ J s)
- A. 1.33 × 10⁻³⁴ kg m/s
- B. 6.63 × 10⁻²⁷ kg m/s
- C. 3.98 × 10⁻¹⁹ kg m/s
- D. 1.33 × 10⁻²⁷ kg m/s
Q8. An electron is confined to a region of width about 1.0 × 10⁻¹⁰ m. Using Δx·Δp ≥ h/4π, what is the minimum uncertainty in its velocity? (h = 6.626 × 10⁻³⁴ J s, m = 9.11 × 10⁻³¹ kg)
- A. 2.3 × 10⁶ m/s
- B. 5.8 × 10³ m/s
- C. 5.8 × 10⁵ m/s
- D. 5.8 × 10⁷ m/s
Q9. The mass defect of a ⁴₂He nucleus is 0.0304 u. What is the binding energy per nucleon? (1 u = 931.5 MeV)
- A. 14.2 MeV
- B. 28.3 MeV
- C. 7.08 MeV
- D. 3.54 MeV
Q10. A radioactive sample initially contains 80 g of an isotope with a half-life of 3 days. How much remains after 12 days?
- A. 2.5 g
- B. 5 g
- C. 20 g
- D. 10 g
Q11. A sample contains 6.0 × 10²⁰ radioactive nuclei with a half-life of 1.0 hour. What is the initial activity? (ln 2 = 0.693)
- A. 6.9 × 10¹⁶ Bq
- B. 4.2 × 10²⁰ Bq
- C. 1.16 × 10¹⁷ Bq
- D. 1.9 × 10¹⁵ Bq
Q12. The living-tissue ¹⁴C activity is 1.0 unit. In an ancient wooden object it is found to be 1/8 of this value. What is the age of the object? (half-life of ¹⁴C = 5730 years)
- A. 11 460 years
- B. 45 840 years
- C. 5730 years
- D. 17190 years
Q13. ²²⁶₈₈Ra emits two α-particles and one β⁻ particle in succession. What are the mass number and atomic number of the final nucleus?
- A. A = 222, Z = 84
- B. A = 218, Z = 85
- C. A = 218, Z = 87
- D. A = 220, Z = 86
Q14. In β⁻ decay a neutron in the nucleus is converted into a proton. Which particles are emitted along with the proton?
- A. An α-particle and a photon
- B. An electron and a neutrino
- C. An electron and an antineutrino
- D. A positron and a neutrino
Q15. Which statement about gamma emission from a nucleus is correct?
- A. The mass number decreases by 4 units
- B. The atomic number decreases by 2
- C. Neither the mass number nor the atomic number changes
- D. The atomic number increases by 1 unit
Q16. Each fission of ²³⁵U releases about 200 MeV. Approximately how many fissions per second are needed to produce 1.0 × 10⁹ W? (1 MeV = 1.6 × 10⁻¹³ J)
- A. 5.0 × 10¹⁹ per second
- B. 3.1 × 10¹⁶ per second
- C. 3.1 × 10¹⁹ per second
- D. 3.1 × 10²² per second
Q17. Why must nuclear fusion take place at extremely high temperatures?
- A. Nuclei must have enough kinetic energy to overcome the Coulomb repulsion between them
- B. High temperatures are needed to produce neutrons
- C. The nuclei must first be broken into protons and neutrons
- D. Fusion only releases energy when the nuclei are molten
Q18. In a nuclear fission reactor, what is the function of the control rods?
- A. To carry heat away from the core
- B. To absorb neutrons and regulate the chain reaction
- C. To slow down fast neutrons
- D. To shield workers from gamma rays
Q19. A 50 kg person absorbs 5.0 J of radiation energy from α-particles whose radiation weighting factor is 20. What is the equivalent dose?
- A. 0.25 Sv
- B. 100 Sv
- C. 0.10 Sv
- D. 2.0 Sv
Q20. The radius of a nucleus is given by R = R₀A^(1/3) with R₀ = 1.2 fm. What is the radius of a nucleus of mass number 125?
- A. 1.2 fm
- B. 6.0 fm
- C. 30 fm
- D. 15 fm
Q21. A spaceship moves at 0.6c relative to Earth. A clock on the ship records an interval of 10 s. What interval does an observer on Earth measure for the same events?
- A. 8.0 s
- B. 12.5 s
- C. 6.0 s
- D. 16.7 s
Q22. What is the minimum photon energy required to produce an electron–positron pair? (electron rest energy = 0.511 MeV)
- A. 2.044 MeV
- B. 0.511 MeV
- C. 1.022 MeV
- D. 0.256 MeV
Q23. Which of the following correctly describes the effect of doping pure silicon with boron?
- A. A p-type semiconductor is formed whose majority carriers are holes
- B. Free electrons are removed and conductivity falls to zero
- C. An n-type semiconductor is formed whose majority carriers are electrons
- D. The band gap becomes zero
Q24. What happens to the width of the depletion layer of a p–n junction diode when it is forward-biased?
- A. It becomes infinite
- B. It increases
- C. It is unchanged
- D. It decreases
Q25. A large capacitor is connected across the output of a rectifier. What is its purpose?
- A. To smooth the output by storing charge when the rectified voltage falls
- B. To block the DC component
- C. To convert the output back to alternating current
- D. To increase the peak value of the AC input
Q26. A Zener diode is mainly used for which purpose?
- A. Amplifying a signal in forward bias
- B. Rectifying alternating current in forward bias
- C. Emitting light in reverse bias
- D. Voltage regulation, operated in reverse breakdown
Q27. A transistor in the common-emitter configuration has β = 100 and a base current of 20 μA. What is the emitter current?
- A. 20.2 mA
- B. 2.02 mA
- C. 0.20 mA
- D. 2.00 mA
Q28. What does the Boolean expression A·B + A·B̄ simplify to?
- A. A·B
- B. A
- C. A + B
- D. B
Q29. An inverting amplifier uses an ideal op-amp with a feedback resistor of 100 kΩ and an input resistor of 10 kΩ. What is the output voltage for an input of +0.20 V?
- A. −2.0 V
- B. +2.0 V
- C. −0.020 V
- D. +20 V
Q30. What is the minimum wavelength of X-rays produced by an X-ray tube operated at 50 kV? (hc = 1240 eV nm)
- A. 0.248 nm
- B. 0.0050 nm
- C. 0.0124 nm
- D. 0.0248 nm