Physics · 4.5.3 The transformer
Transformer. Step it.
Change the turns on each coil and watch the output voltage follow Vp/Vs = Np/Ns. For an ideal transformer power is conserved (VpIp = VsIs), so stepping voltage up steps current down. This is how the grid transmits power efficiently.
0625 Topic 4.5.3 — Transformer
Vp/Vs = Np/Ns
Ideal: VpIp = VsIs
Variables
12
100
200
1.0
Live readouts
Turns ratio Ns/Np
2.00
Output voltage Vs
24.0 V
Type
step-up
Primary current Ip
2.00 A
Power (ideal)
24 W
Ideal transformer: VpIp = VsIs. Step voltage up → current steps down (and vice versa). Only works with a.c.
📋 How it works (Cambridge)
- An alternating current in the primary coil produces a continually changing magnetic field in the soft-iron core.
- The changing field links the secondary coil and induces an alternating EMF in it.
- Vp/Vs = Np/Ns. More secondary turns → step-up; fewer → step-down.
- For an ideal (100% efficient) transformer, VpIp = VsIs.
- The grid steps voltage up for transmission so current — and therefore I²R heating loss in the cables — is small, then steps it back down for homes.
- Only works with a.c.; a steady d.c. gives a constant field and no induced EMF.
🎯 Syllabus reference (0625)
- 4.5.3 Transformer — describe the construction and action of a transformer; recall and use Vp/Vs = Np/Ns; recall and use VpIp = VsIs for an ideal transformer; explain the use of high voltage for efficient power transmission.