02 Transformer

02 Transformer#

Aim#

To verify the relationship between the voltages and the number of turns in the coils.

Subjects#

  • 5K30 (Transformers)

Diagram#

../../../../../_images/figure_0219.png

Fig. 542 .#

Equipment#

  • \(220 mathrm{~V}\) mains safety switchbox.

  • U-core with bar and clamping device.

  • Coil, \(n=500\).

  • Multi scale voltmeter with large display.

  • Long wire.

Safety#

  • Applying the \(220 mathrm{~V}\) mains is done via a safety switch box that switches both connectors ON/OFF. When ON, a red light appears on the box; when OFF a green light shows, indicating that it is safe to manipulate the circuit.

Presentation#

The demonstration is set up as shown in Diagram and Figure 543.

../../../../../_images/figure_1174.png

Fig. 543 .#

The \(220 \mathrm{~V}\) is switched on and the students can read on the \(\mathrm{V}\)-meter that in the loop around the core a voltage of around \(.4 \mathrm{~V}\) is induced.

Then the demonstrator makes the wire go round the core in two loops. Again the induced voltage is read and a doubling is observed. Then make the wire go round the core three times (see Figure 544). And so on, as long as the length of the wire enables it.

../../../../../_images/figure_297.png

Fig. 544 .#

Clearly the proportionality between induced voltage and the number of turns is observed.

Explanation#

When an alternating voltage \(\left(E_{p}\right)\) is applied across the primary coil of a transformer and there is no flux leakage, then the emf induced in the secondary coil is given by: \(E_{s}=\frac{n_{s}}{n_{p}} E_{p}\). This demonstration verifies this:

  • 1 turn: \(E_{\mathrm{s}}=1 / 500(220)=.44 \mathrm{~V}\).

  • 2 turns: \(E_{s}=2 / 500(220)=.88 \mathrm{~V}\).

  • Etc.

Sources#

  • Mansfield, M and O’Sullivan, C., Understanding physics, pag. 527-529

Contents