A characteristic of diodes is that current flows (forward direction) or current does not flow (reverse direction) depending on the direction of applied voltage.

to use one or more diodes, those handy electronic components that allow current current to pass in one direction

A transformer that increases the voltage from primary to secondary is called a step-up transformer,the opposite is called a step-down transformer.

The SI unit of magnetic flux is the weber (Wb; in derived units, volt–seconds),

about 0.6 to 0.7 volts

The transformer works on basic principles of electromagnetic induction and mutual induction.

Cell phones, Flat-screen TVs (AC goes into the TV, which is converted to DC) Flashlights. Hybrid and electric vehicles., remote controle, etc.

most diodes are made of silicon, but other semiconducting materials such as gallium arsenide and germanium are also used.

It is commonly used to increase or decrease the supply voltage without a change in the frequency of AC between circuits.

What type of rectifier uses four diodes to convert the AC to DC?

The RMS value is the square root of the mean (average) value of the squared function of the instantaneous values

an iron core,primary winding and secondary winding or coil of wire.

generated in the iron core due to changing magnetic flux, reduced by using thin sheets of magnetic material (laminations)