The Rectifier is an electronic device, which converts an AC waveform(Usually a Bi-directional waveform with Zero Average value) to a Pulsating DC waveform (Uni-directional waveform with Nonzero Average value). As AC wave (Sinusoidal) has two half cycles, namely - Positive Half cycle & Negative Half cycle If a Rectifier does it's operation only in one half of the cycles, it is known as Half Wave Rectifier. Similarly, If a Rectifier does it's operation in both the half cycles, it is known as Full Wave Rectifier.
what is the function of transformer in the half wave rectifier circuit
They both have the same current.
Its no longer a rectifier and the resistors may catch fire.
A rectifier allows current to flow only in one direction. In a half-wave rectifier circuit, an input wave which oscillates between positive and negative, will 'pass through' the positive portion of the wave, and when the input is negative will output zero. A full-wave rectifier circuit, is commonly configured with 4 rectifier diodes, which allow a positive wave to output when the input wave is negative.
a 2 diode rectifier is a center tap rectifier an a 4 diode rectifier will be a bridge rectifier *********************************************************** A two-diode rectifier is not always a centre-tap rectifier. If the two diodes are connected to the same end of a transformer's secondary, one by its anode and one by its cathode, one will proved a positive voltage with respect to trhe other end of the winding and the other will provide a negative voltage. (But perhaps that isn't considered a two-diode rectifier - but a two single-diode ones.)