# S-Cool Revision Summary

## S-Cool Revision Summary

#### Transformers

The great thing about a.c. electricity is that you can transform it! For instance, you can step its voltage up or down.

Transformers work on the principles of **electromagnetism and electromagnetic induction.**

The iron core increases the flux density (or field strength) in the secondary coils. The larger the number of coils, the greater the flux linkage and therefore the greater the induced e.m.f. in the secondary coil.

You must have an alternating current in the primary coil or the field will not be changing and no emf will be induced in the secondary.

#### The Turns Rule

**If you change the number of turns in the coils you change the induced emf.** This allows you to change (transform) the voltage from the primary to the secondary coil.

**The Turns Rule is:**

*Where:*

N_{s} = number of turns on the secondary coil

N_{p} = number of turns on the primary coil

V_{s} = voltage across the secondary coil

V_{p} = voltage across the primary coil

#### Rectifying A.C.

You should be able to draw circuits and outputs for half wave and full wave rectification circuits.

Placing a capacitor in parallel with the resistor smoothes the current through the resistor by providing extra charge when the supply voltage drops.

#### Equations

*Transformers*

**The turns rule:**

#### Symbols

*Transformers*

N_{s} = the number of turns in the secondary coil

N_{p} = the number of turns in the primary coil

V_{s} = the voltage in the secondary coil

V_{p} = the voltage in the primary coil

I_{s} = the current in the secondary coil

I_{p} = the current in the primary coil