Number of entities

Prof. Dr. Thorsten Jungmann (last updated 2025-09-04)

The number of entities (German: Menge, also Quantität) describes the count of objects, components or events. In electrical engineering, it is relevant, among other things, for numbers of pieces, the number of turns of inductors and the number of charge carriers.

1 Quantity symbol and unit

The quantity symbol for the number of entities is $N$ or $n$ (depending on the context). The number of entities is a dimensionless quantity with the unit ‘1’ (one) or ‘piece’.

[N] = 1

2 Practical and worked examples

2.1 Number of turns of an inductor

The inductance of an inductor depends on the square of the number of turns:

L = μ_{0} \cdot μ_{r} \cdot \frac{N ^{2} \cdot A}{l}

Example: doubling the number of turns from $N_{1} = 100$ to $N_{2} = 200$

L_{2} = L_{1} \cdot (\frac{N _{2}}{N _{1}})^{2} = L_{1} \cdot (\frac{200}{100})^{2} = \underline{4 \cdot L_{1}}

2.2 Number of electrons in an electric charge

The number $n$ of electrons in an electric charge $Q$ :

n = \frac{Q}{e}

Example: $Q = 1.6 nC$ , elementary charge $e = 1.602 \cdot 1 0^{- 19} C$

n = \frac{1.6 \cdot 1 0 ^{- 9} C}{1.602 \cdot 1 0 ^{- 19} C} = \underline{1.0 \cdot 1 0^{10}}

3 Typical orders of magnitude

Number of turns of small inductors: $10$ to $1000$
Number of turns of transformers: $100$ to $10000$
Electrons per coulomb: $6.242 \cdot 1 0^{18}$
Components on printed circuit boards: $10$ to $1000$ (pieces)

4 Example phrasings

‘The inductor has a number of turns of $N = 250$ .’
‘The transformer has $N_{1} = 230$ turns on the primary side and $N_{2} = 12$ turns on the secondary side.’
‘One coulomb contains about $6.24 \cdot 1 0^{18}$ electrons.’

Inductance via the number of turns:

L \propto N^{2}

Electric charge and number of electrons:

Q = n \cdot e

Magnetomotive force:

Θ = N \cdot I

Inductor: the number of turns determines the electrical properties
Transformer: the turns ratio determines the transformation ratio
Relay: the number of turns influences the pick-up current

Wattsinside

Number of entities

1 Quantity symbol and unit

2 Practical and worked examples

2.1 Number of turns of an inductor

2.2 Number of electrons in an electric charge

3 Typical orders of magnitude

4 Example phrasings

Table of Contents

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Wattsinside

Number of entities

1 Quantity symbol and unit

2 Practical and worked examples

2.1 Number of turns of an inductor

2.2 Number of electrons in an electric charge

3 Typical orders of magnitude

4 Example phrasings

5 Related quantities

6 Related components

Table of Contents

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