Physical constants and their values

Values worth memorising for numericals

Most JEE and NEET papers give the constants they need, but knowing these saves time and lets you check an answer's order of magnitude:

• hc = 1240 eV nm. The energy of a 620 nm photon is 1240 ÷ 620 = 2 eV, no conversion needed.
• 1 u = 931.5 MeV. Multiply a mass defect in u by 931.5 to get the binding energy in MeV.
• 1/4πε₀ = 9 × 10⁹. Shows up in every electrostatics problem.
• Hydrogen energy levels: Eₙ = −13.6/n² eV.

Check that your formula is right with dimensional formulas, and round your answer properly with the significant figures calculator.

Each constant on its own page

Every value in different units, and which one to use:

• Gas constant (R): 8.314 J mol⁻¹ K⁻¹
• Planck's constant (h): 6.626 × 10⁻³⁴ J s
• Avogadro's number (Nₐ): 6.022 × 10²³ mol⁻¹
• Speed of light (c): 3 × 10⁸ m/s
• Charge of an electron (e): 1.602 × 10⁻¹⁹ C
• Mass of an electron (mₑ): 9.109 × 10⁻³¹ kg
• Mass of a proton (mₚ): 1.673 × 10⁻²⁷ kg
• Mass of a neutron (mₙ): 1.675 × 10⁻²⁷ kg
• Universal gravitational constant (G): 6.674 × 10⁻¹¹ N m² kg⁻²
• Acceleration due to gravity (g): 9.8 m/s²
• Boltzmann constant (k): 1.381 × 10⁻²³ J/K
• Faraday constant (F): 96 485 C/mol
• Permittivity of free space (ε₀): 8.854 × 10⁻¹² C² N⁻¹ m⁻²
• Permeability of free space (μ₀): 4π × 10⁻⁷ T m/A
• Rydberg constant (R): 1.097 × 10⁷ m⁻¹
• Stefan–Boltzmann constant (σ): 5.67 × 10⁻⁸ W m⁻² K⁻⁴
• Wien's constant (b): 2.898 × 10⁻³ m K
• Bohr radius (a₀): 0.529 Å
• Molar volume of a gas at STP (Vₘ): 22.4 L/mol

Questions students ask

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