Specific Charge, Protons & Neutron Numbers
Physics: AQA A Level, topic 2.1.2
Specific Charge
Charged particles can be described in terms of their specific charge.
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)
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.
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.
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.
Test yourself on Specific Charge, Protons & Neutron Numbers
What are the standard units for specific charge?
What is the specific charge of a neutron?
What is the nucleon number?
Which of the following are true of proton and nucleon numbers?