Physics Electronics NUMS 2024
PMDC Verified Question 451 of 494
For rectification transformer used is:
A
With low input voltage
B
Step up
C
Step down
D
With low input resistance
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: Step down
Concept:

Most electronic devices operate on low-voltage Direct Current (DC), but power grids supply high-voltage Alternating Current (AC).

Solution:

  • Mains AC is typically \( 220\text{V} \) or \( 110\text{V} \). Electronic circuits (like phones and laptops) require much lower voltages (e.g., \( 5\text{V} \), \( 12\text{V} \)).


  • Before rectification occurs, the high mains voltage must be lowered to a safe, usable level to prevent destroying the diodes.


  • A Step down transformer is utilized at the very beginning of the power supply to achieve this voltage reduction.


Why other options are incorrect:

  • Step up: Would dangerously increase the voltage, destroying the circuit.


  • Low input voltage / Low input resistance: Do not describe the fundamental function of the transformer in this context.

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