Specific Charge, Protons & Neutron Numbers

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Specific Charge

Charged particles can be described in terms of their specific charge.

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Specific charge

  • Specific charge is calculated by dividing the charge of a particle (in coulombs) by its mass (in kilograms):
    • Specific charge (C/kg) = charge (C) ÷ mass (kg)
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Example: sodium ion

  • A sodium ion has a mass of 23 proton masses (mp).
    • This is 3.85 × 10-26kg.
  • It also has a charge of +1 electron charges (e).
    • This means its charge is 1.60 × 10-19C.
  • So:
    • Specific charge = (1.60 × 10-19C) ÷ (3.85 × 10-26kg)
    • Specific charge = 4.16 × 106C/kg

Proton and Nucleon Numbers

Proton numbers and nucleon numbers tell us information about atoms.

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Proton number (Z)

  • The number of protons in a nucleus tells us what element an atom is.
  • For example, hydrogen atoms always have 1 proton.
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Nucleon number (A)

  • The nucleon number is the total number of protons and neutrons in a nucleus.
  • Atoms of the same element can have different numbers of neutrons.
  • For example, hydrogen can have 0, 1 or 2 neutrons.

Jump to other topics

1Measurements & Errors

2Particles & Radiation


4Mechanics & Materials


6Further Mechanics & Thermal Physics (A2 only)

7Fields & Their Consequences (A2 only)

8Nuclear Physics (A2 only)

9Option: Astrophysics (A2 only)

10Option: Medical Physics (A2 only)

11Option: Engineering Physics (A2 only)

12Option: Turning Points in Physics (A2 only)

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