Physics practice: units, fluids, oscillations and nuclear changes

These 32 self-contained practice questions develop the calculations and distinctions used in premedical physics. They are a practice set, not a verified reproduction of an official past paper. Work out the result before opening each answer, then use the separate quiz to test recall.

Three checks that prevent misleading answers

Read what is measured. A scale measures the support force; it does not directly measure the gravitational force. A freely falling person can have a zero scale reading while gravity remains nonzero.

Keep the assumptions attached to the formula. The Carnot efficiency formula applies to a reversible engine, not every engine with the same reported efficiency. Bernoulli’s equation requires a suitable ideal-flow model.

Count nuclear changes separately. For one alpha emission followed by one beta-minus emission, start from the original atomic number, subtract two, then add one. Never infer a missing diagram or select a remembered answer when the stated information cannot determine it.

Practice questions and worked answers

1. The formula for electric field strength is ‘E = F/Q’. Correct base units?

  1. kg m s⁻³ A⁻¹
  2. kg s⁻² A⁻³
  3. kg² m⁻² s⁻³ A
  4. m s⁻¹ A⁻³
Answer and explanation

A: kg m s⁻³ A⁻¹

E = F/q → kg m s⁻² / (A s) = kg m s⁻³ A⁻¹

2. Which set of prefixes gives values in increasing order?

  1. Pico, Mega, Kilo, Tera
  2. Pico, Micro, Mega, Giga
  3. Tera, Pico, Micro, Kilo
  4. Giga, Kilo, Milli, Nano
Answer and explanation

B: Pico, Micro, Mega, Giga

pico (10⁻¹²) < micro (10⁻⁶) < mega (10⁶) < giga (10⁹)

3. Oil film on water shows colour pattern due to:

  1. Diffraction
  2. Polarization
  3. Interference
  4. Surface tension
Answer and explanation

C: Interference

Thin film interference of reflected light

4. Best graph for drag force F vs speed v (low speed, viscous fluid)?

  1. Straight line through origin
  2. Parabolic upward
  3. Horizontal line
  4. Exponential
Answer and explanation

A: Straight line through origin

Stokes’ law: F = 6πηrv → F ∝ v (linear)

5. An open tank has a small outlet 5 m below its water surface. Neglect viscosity and surface speed; both surface and outlet are at atmospheric pressure. For g = 10 m/s², what is the exit speed?

  1. 5 m/s
  2. 10 m/s
  3. 2 m/s
  4. 50 m/s
Answer and explanation

B: 10 m/s

v = √(2gh) = √100 = 10 m/s

6. For steady incompressible, non-viscous flow along a streamline in a horizontal pipe, which quantity is constant?

  1. P + ρv² = constant
  2. 2P + ρv² = constant
  3. P + 2ρv² = constant
  4. 2P + 2ρv² = constant
Answer and explanation

B: 2P + ρv² = constant

Bernoulli’s equation gives P + ½ρv² = constant at fixed height. Multiplying every term by 2 gives 2P + ρv² = constant, which is option B. The factor ½ cannot be discarded from just one term.

7. Least distance of distinct vision for normal eye:

  1. 20 cm
  2. 25 cm
  3. 10 cm
  4. 15 cm
Answer and explanation

B: 25 cm

Standard value = 25 cm

8. Atomic distance 0.30 nm, θ=30°, 1st order λ?

  1. 0.60 nm
  2. 0.30 nm
  3. 0.20 nm
  4. 0.90 nm
Answer and explanation

B: 0.30 nm

λ = 2d sinθ = 2×0.3×0.5 = 0.30 nm

9. A 100 kg person stands on a scale in an elevator that is in free fall. What is the scale reading, neglecting air resistance?

  1. 1000 N
  2. 10 N
  3. 500 N
  4. Zero
Answer and explanation

D: Zero

The scale measures the normal force, which becomes zero in free fall. Gravity still acts on the person; gravitational force and apparent weight are different quantities.

10. For a small-amplitude simple pendulum of length 9.8 m with g = 9.8 m/s², what is its frequency?

  1. 2π Hz
  2. π/2 Hz
  3. 1/(2π) Hz
  4. π/4 Hz
Answer and explanation

C: 1/(2π) Hz

T=2π s → f=1/(2π) Hz

11. SHM: T=0.063 s, v_max=3 m/s. xo & ω?

  1. 0.03 m, 100 rad/s
  2. 0.19 m, 16 rad/s
  3. 5.3 m, 16 rad/s
  4. 3.3 m, 100 rad/s
Answer and explanation

A: 0.03 m, 100 rad/s

ω≈100 rad/s, xo=3/100=0.03 m

12. What primarily transfers microwave energy to water-containing food in an ordinary microwave oven?

  1. Nuclear fission
  2. Dielectric heating by an alternating electric field
  3. Visible-light absorption
  4. A decrease in molecular motion
Answer and explanation

B: Dielectric heating by an alternating electric field

The alternating electric field interacts with polar molecules. Energy is dissipated through molecular interactions as heat. Calling ordinary microwave cooking a sharp resonance of water molecules is misleading.

13. On an energy-versus-displacement graph, how is the total mechanical energy of an ideal, undamped spring oscillator represented?

  1. Downward parabola
  2. Upward parabola
  3. Horizontal line
  4. Sinusoidal
Answer and explanation

C: Horizontal line

E = constant (horizontal)

14. A cubic container of side a holds N gas molecules, each of mass m. What is the gas density?

  1. N/a²
  2. m/a³
  3. Nm/a³
  4. Na³/m
Answer and explanation

C: Nm/a³

ρ = (N m) / a³

15. In PV=nRT, n = ?

  1. N NA
  2. N / NA
  3. NA / N
  4. N + NA
Answer and explanation

B: N / NA

n = molecules / Avogadro number

16. For a graph with tensile stress on the vertical axis and tensile strain on the horizontal axis, what gives Young’s modulus in the linear elastic region?

  1. Area under graph
  2. Gradient
  3. Reciprocal of gradient
  4. Gradient × area
Answer and explanation

B: Gradient

Y = slope in elastic region

17. Temperature where °C = °F?

  1. -100°
  2. -40°
  3. -180°
  4. -273°
Answer and explanation

B: -40°

Solve C = F → -40°

18. A reversible Carnot engine has efficiency 50% and a hot reservoir at 327°C. Approximately what is the cold-reservoir temperature?

  1. 27°C
  2. 127°C
  3. 300°C
  4. 600°C
Answer and explanation

A: 27°C

For a Carnot engine, η = 1 − Tc/Th, with temperatures in kelvin. Th ≈ 600 K, so Tc ≈ 300 K or 27°C. Efficiency alone would not determine Tc for an arbitrary real engine.

19. x = AB + A'B' is which gate?

  1. XOR
  2. XNOR
  3. AND
  4. OR
Answer and explanation

B: XNOR

XNOR (1 when A=B)

20. An ideal parallel-plate capacitor in vacuum has plate area 2 m² and separation 2 mm. Neglect edge effects. What is its capacitance?

  1. 4×10⁻³ F
  2. 3.54×10⁻⁹ F
  3. 8.85×10⁻⁹ F
  4. 9.0×10⁻⁹ F
Answer and explanation

C: 8.85×10⁻⁹ F

C=ε₀A/d = 8.85×10⁻⁹ F

21. Using the ideal long-solenoid approximation, a coil has 300 turns over 15 cm and carries 5 A. What magnetic flux density does B = μ₀(N/L)I predict?

  1. 75×10⁻⁷ T
  2. 60×10³ T
  3. 4π×10⁻³ T
  4. 750π×10⁻³ T
Answer and explanation

C: 4π×10⁻³ T

B=μ₀ n I = 4π×10⁻³ T

22. In ideal stimulated emission, how does the emitted photon’s wavelength compare with that of the stimulating photon?

  1. λA = λB
  2. λA > λB
  3. λA < λB
  4. λA = 2λB
Answer and explanation

A: λA = λB

Identical photons

23. Bones absorb more X-rays because:

  1. Lie between flesh
  2. Light color
  3. Low density
  4. High density
Answer and explanation

D: High density

Compared with surrounding soft tissue, bone attenuates X-rays more strongly because of its density and composition, including elements with higher atomic numbers. Colour is irrelevant to X-ray attenuation.

24. Practical application of X-rays:

  1. MRI
  2. Ultrasonography
  3. Computerized Axial Tomography
  4. PET
Answer and explanation

C: Computerized Axial Tomography

CT scan uses X-rays

25. Typical X-ray tube output spectrum:

  1. Continuous + characteristic peaks
  2. Only sharp lines
  3. Only continuous
  4. Discrete only
Answer and explanation

A: Continuous + characteristic peaks

Bremsstrahlung + characteristic

26. Energy of electron at 2 kV for X-rays?

  1. 2×10⁻¹⁹ J
  2. 1.6×10⁻¹⁹ J
  3. 3.2×10¹⁹ J
  4. 3.2×10⁻¹⁶ J
Answer and explanation

D: 3.2×10⁻¹⁶ J

E = eV = 3.2×10⁻¹⁶ J

27. 3D images using laser beam called:

  1. Photography
  2. 3-D cinema
  3. Holography
  4. Tomography
Answer and explanation

C: Holography

Holography

28. β⁻ decay change:

  1. Z same, A+1
  2. Z+1, A-2
  3. Z+1, A same
  4. Z-2, A-4
Answer and explanation

C: Z+1, A same

Neutron → proton + e⁻

29. If a uranium nucleus (Z = 92) emits one alpha particle and then one beta-minus particle, what is the daughter atomic number?

  1. 90
  2. 91
  3. 89
  4. 88
Answer and explanation

B: 91

Alpha emission changes Z by −2; beta-minus emission changes Z by +1. Therefore Z = 92 − 2 + 1 = 91. The net mass-number change is −4. This is nuclear bookkeeping for the stated sequence, not a claim about the dominant natural decay chain.

30. Two alpha decays: daughter Z & A change?

  1. Z-4 A-2
  2. Z-2 A-4
  3. Z-4 A-8
  4. Z-8 A-4
Answer and explanation

C: Z-4 A-8

Each α: Z-2 A-4 → total Z-4 A-8

31. A hypothetical decay sequence contains one beta-minus emission followed by two alpha emissions. What is the net change in atomic number?

  1. +3
  2. -3
  3. +5
  4. -5
Answer and explanation

B: -3

+1 -2 -2 = -3

32. Absorbed dose: 100 J in 2 kg sample?

  1. 200 Gy
  2. 102 Gy
  3. 50 Gy
  4. 98 Gy
Answer and explanation

C: 50 Gy

D = 100 / 2 = 50 Gy

Interactive quiz

Select answers and submit when ready. Unanswered questions receive no marks; the worked answers above explain each result.

Frequently asked questions

What assumptions does Bernoulli’s equation use?

The standard equation assumes steady, incompressible flow without viscous energy losses along a streamline. A pump or substantial friction requires additional energy terms.

How are flow rate and fluid speed different?

Flow rate is volume passing a section per unit time; speed is distance travelled per unit time. For uniform flow through area A, the volume flow rate is Av.

How can Carnot-engine efficiency be increased?

Raise the hot-reservoir temperature or lower the cold-reservoir temperature, comparing both in kelvin. The ideal limit is 1 − Tc/Th.

Can a Carnot engine reach 100% efficiency?

A Carnot engine would require a cold reservoir at absolute zero to reach 100% efficiency for a finite hot temperature. That condition is not physically attainable.

Does beta-minus decay change mass number?

Beta-minus decay leaves mass number unchanged and raises atomic number by one. A neutron becomes a proton while an electron and an antineutrino are emitted.

How is alpha decay different from beta decay?

Alpha decay removes two protons and two neutrons, reducing Z by two and A by four. Beta-minus decay changes a neutron into a proton, leaving A unchanged.

References