More turns, stronger field
The fields of the turns add up.
One turn or many
A wire is bent into one circular turn and a current flows. Then the same wire is wound into a coil of 5 turns, with the same current.
How does the field of the coil compare with the field of one turn?
What this lesson covers
The idea
Since the current in each turn of a circular coil has the same direction, the fields of the turns add up, so a coil of n turns produces a field n times that of a single turn.
One turn or many
A wire is bent into one circular turn and a current flows. Then the same wire is wound into a coil of 5 turns, with the same current.
How does the field of the coil compare with the field of one turn?
- It is 5 times as large
- It is the same
- It is 5 times smaller
Add turns
Press + to add turns. Watch the bar for the field of the coil.
The turns add up
In a coil, the current in each turn goes round the same way. So the field made by each turn points the same way inside the coil, and the fields just add. With n turns the field is n times the field of one turn.
The current in each turn of a circular coil has the same direction, so the fields of the turns add up: a coil of n turns produces a field n times that of a single turn.
Notes
A coil of n turns gives a field n times that of a single turn, because the current has the same direction in each turn and the fields add up.
Check yourself
Why do the fields of the turns of a coil add up?
A coil has n turns, with the same current. Compared with a single turn its field is…
In an example, one turn of a coil gives a field of 3 units at a point (units chosen for this lesson). A coil of 5 turns with the same current gives how many units at that point?
Answer: 15 units
A coil of n turns gives n times the field of one turn: 5 × 3 = 15 units.
In an example, a coil with the same current gives 12 units, and one turn of it alone gives 3 units. How many turns does the coil have?
Answer: 4 turns
Field of the coil = n × field of one turn, so n = 12 ÷ 3 = 4.
- The current in each turn has the same direction — correct. Yes!
- Each turn carries the current in a different direction. If the turns carried the current in different directions the fields would not just add. They add because the current has the same direction in each turn.
- The turns are made of different wires. It is the same direction of the current in each turn that makes the fields add up.
- the same. The fields of the turns add up, so the coil gives more than one turn.
- n times as large — correct. Yes!
- n times smaller. More turns make the field larger, not smaller.