Question
The masses of atoms and subatomic particles are extremely small, so scientists use the atomic mass unit (u) instead of the kilogram. What is the approximate value of 1 u in SI units?
This question was previously asked in
RRB Technician 2026 Grade 3 Question Paper (7-Oct-2026) (Shift 3)
The correct answer is
1.66×10−27 kg
1 atomic mass unit is defined as \(\frac{1}{12}\) of the mass of one carbon-12 atom.
Mass of a carbon-12 atom ≈ \(1.9926 \times 10^{-26}\) kg, so 1 u = \(\frac{1.9926 \times 10^{-26}}{12} \approx 1.66 \times 10^{-27}\) kg.
This is close to the mass of a proton or neutron (≈ \(1.67 \times 10^{-27}\) kg).
Hence, the answer is 1.66×10−27 kg.
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