NUMS — Medical & Dental Entry Test

NUMS Physics — Electronics, Modern and Nuclear Physics (Set 1)

Take the NUMS Physics — Electronics, Modern and Nuclear Physics (Set 1): 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. Pure silicon is doped with a small amount of phosphorus (Group 15). What type of semiconductor is produced?
- A. An intrinsic semiconductor
- B. n-type, with electrons as majority carriers ✓
- C. n-type, with holes as majority carriers
- D. p-type, with holes as majority carriers
Answer: B. n-type, with electrons as majority carriers
Explanation: Phosphorus has five valence electrons; four bond with silicon and the fifth becomes a free electron, so the material is n-type.
Q2. Which dopant added to germanium produces a p-type semiconductor?
- A. Antimony
- B. Boron ✓
- C. Phosphorus
- D. Arsenic
Answer: B. Boron
Explanation: Boron is trivalent; each atom leaves one bond incomplete, creating a hole. The others are pentavalent donors.
Q3. When a p–n junction diode is forward biased, what happens to the depletion region?
- A. It is unchanged
- B. It becomes wider and current increases
- C. It becomes wider and current stops
- D. It becomes narrower and current flows easily ✓
Answer: D. It becomes narrower and current flows easily
Explanation: Forward bias opposes the barrier potential, pushing carriers toward the junction and shrinking the depletion layer.
Q4. How many diodes are needed in a bridge circuit for full-wave rectification?
- A. 1
- B. 6
- C. 4 ✓
- D. 2
Answer: C. 4
Explanation: A bridge rectifier uses four diodes so that both half-cycles drive current through the load in the same direction.
Q5. In a transistor amplifier, the base current is 20 μA and the collector current is 2 mA. What is the current gain β?
- A. 1000
- B. 40
- C. 100 ✓
- D. 10
Answer: C. 100
Explanation: β = Ic/Ib = 2 × 10⁻³/20 × 10⁻⁶ = 100.

The other 25 questions

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Q6. For which input combination does a two-input NAND gate give output 0?
- A. A = 0, B = 0
- B. A = 1, B = 0
- C. A = 0, B = 1
- D. A = 1, B = 1
Q7. A comparator circuit lights a warning lamp when two sensor signals disagree (one HIGH, one LOW) and keeps it off when they agree. Which single gate does this?
- A. NOR
- B. AND
- C. XOR
- D. XNOR
Q8. Which pair of devices correctly matches a p–n junction to its usual biasing?
- A. Both reverse biased
- B. Both forward biased
- C. LED forward biased; photodiode reverse biased
- D. LED reverse biased; photodiode forward biased
Q9. Photons of energy 5 eV strike a metal surface whose work function is 2 eV. What is the stopping potential for the emitted photoelectrons?
- A. 5 V
- B. 3 V
- C. 2.5 V
- D. 7 V
Q10. In a photoelectric experiment, the intensity of the light (above threshold frequency) is doubled. What is the effect?
- A. The number of emitted electrons doubles but their maximum KE is unchanged
- B. No electrons are emitted
- C. The maximum KE of the electrons doubles
- D. Both the number and the maximum KE double
Q11. What is the energy of a photon of orange light of wavelength 600 nm? (hc = 1240 eV nm)
- A. 0.48 eV
- B. 2.07 eV
- C. 1.24 eV
- D. 20.7 eV
Q12. An electron in an electron microscope is accelerated from rest through 150 V. What is its approximate de Broglie wavelength? (λ ≈ 1.226/√V nm)
- A. 8.2 nm
- B. 0.1 nm
- C. 0.01 nm
- D. 1.0 nm
Q13. When X-ray photons are scattered by free electrons in a target (Compton effect), how does the wavelength of the scattered X-rays compare with the incident X-rays?
- A. It is unchanged
- B. It becomes zero
- C. It is longer
- D. It is shorter
Q14. A high-energy gamma photon passing near a nucleus can vanish and create an electron together with its antiparticle. Below what photon energy is this impossible?
- A. 1.02 MeV
- B. 931 MeV
- C. 13.6 eV
- D. 0.51 MeV
Q15. A diagnostic X-ray tube operates at 30 kV. What is the shortest wavelength of X-rays it produces? (hc = 1240 eV nm)
- A. 4.1 nm
- B. 0.41 nm
- C. 0.0041 nm
- D. 0.041 nm
Q16. A clock on a spacecraft moving at 0.6c records an interval of 10 s. How long does this interval last for an observer on Earth?
- A. 16.7 s
- B. 8 s
- C. 10 s
- D. 12.5 s
Q17. Heisenberg's uncertainty principle sets a lower limit on the product of uncertainties in which pair of quantities?
- A. Velocity and acceleration
- B. Mass and charge
- C. Wavelength and frequency
- D. Position and momentum
Q18. Lasers used in eye surgery rely on 'population inversion'. What does this term mean?
- A. Atoms emit photons spontaneously in random directions
- B. More atoms are in a higher (metastable) energy state than in the lower state
- C. Electrons are removed completely from the atoms
- D. All atoms are in the ground state
Q19. Nuclear radius is given by R = R₀A^(1/3). How does the radius of a nucleus of mass number 216 compare with one of mass number 27?
- A. Twice as large
- B. Four times as large
- C. Three times as large
- D. Eight times as large
Q20. A nucleus has a mass defect of 0.1 u. What is its binding energy? (1 u ≡ 931.5 MeV)
- A. 93.15 MeV
- B. 0.1 MeV
- C. 931.5 MeV
- D. 9.315 MeV
Q21. Near which element does the curve of binding energy per nucleon reach its maximum, making that nucleus the most stable?
- A. Iron-56
- B. Hydrogen-2
- C. Uranium-235
- D. Helium-4
Q22. Radium-226 (Z = 88) decays by emitting one alpha particle. What is the daughter nucleus?
- A. Mass number 222, atomic number 86
- B. Mass number 222, atomic number 87
- C. Mass number 226, atomic number 89
- D. Mass number 224, atomic number 86
Q23. In beta-minus decay, what change takes place inside the nucleus?
- A. A proton changes into a neutron, emitting a positron
- B. Two protons and two neutrons are emitted together
- C. An orbital electron is captured by the nucleus
- D. A neutron changes into a proton, emitting an electron and an antineutrino
Q24. Technetium-99m, used in bone scans, has a half-life of 6 hours. A dose has an activity of 160 MBq when injected. What is its activity 24 hours later?
- A. 40 MBq
- B. 5 MBq
- C. 10 MBq
- D. 20 MBq
Q25. Which type of nuclear radiation is the most penetrating but the least ionising?
- A. Alpha particles
- B. Protons
- C. Gamma rays
- D. Beta particles
Q26. In a thermal nuclear reactor, what is the main function of the moderator (such as heavy water or graphite)?
- A. To absorb excess neutrons and stop the reaction
- B. To slow down fast neutrons so they can cause further fission of U-235
- C. To shield workers from gamma rays
- D. To carry heat to the turbines
Q27. What is the main source of the Sun's energy?
- A. Fusion of hydrogen nuclei into helium
- B. Fission of uranium nuclei
- C. Radioactive decay of radium
- D. Combustion of hydrogen gas
Q28. What is the SI unit of absorbed radiation dose, defined as one joule of energy absorbed per kilogram of tissue?
- A. Gray (Gy)
- B. Curie (Ci)
- C. Becquerel (Bq)
- D. Sievert (Sv)
Q29. Iodine-131, used in thyroid therapy, has a half-life of 8 days. What is its decay constant?
- A. 0.693 day⁻¹
- B. 5.54 day⁻¹
- C. 0.125 day⁻¹
- D. 0.0866 day⁻¹
Q30. Uranium-238 (Z = 92) decays through a series to stable lead-206 (Z = 82). How many alpha and beta-minus particles are emitted in total?
- A. 8 alpha and 8 beta
- B. 6 alpha and 8 beta
- C. 10 alpha and 2 beta
- D. 8 alpha and 6 beta