Consider the following statements regarding AC voltage controller:1.Controls RMS output voltage.2.Uses phase angle control.3.Works only with resistive load.4.Used in light dimmers.Which of the statements are correct?

Correct Answer: A - 1, 2 and 4 only

Quick Concept Explanation

Unlike an inverter, an AC voltage controller does not change AC to a new frequency; it controls the portion of each source cycle applied to the load. With phase control, delaying the firing angle reduces RMS output. Key relation: For a resistive single-phase phase-controlled load, Vrms depends on firing angle α; frequency at the load remains the source frequency.

Exam focus: AC controller → same frequency, variable RMS voltage. Common trap: Confusing an AC voltage controller with a frequency converter/inverter.

Statement-wise Verification

• Statement 1 - Correct.
  Controls RMS output voltage.
  The controller changes the RMS value of the AC output while input frequency remains unchanged.
• Statement 2 - Correct.
  Uses phase angle control.
  Phase-angle control is a standard firing method for thyristor/triac AC controllers.
• Statement 3 - Incorrect.
  Works only with resistive load.
  AC voltage controllers are used with R, RL and other practical loads; inductive-load analysis simply changes current extinction/firing behavior.
• Statement 4 - Correct.
  Used in light dimmers.
  Light dimmers are a classic low-power application.

Core Concept

Unlike an inverter, an AC voltage controller does not change AC to a new frequency; it controls the portion of each source cycle applied to the load. With phase control, delaying the firing angle reduces RMS output.

Formula / Key Relationship

For a resistive single-phase phase-controlled load, Vrms depends on firing angle α; frequency at the load remains the source frequency.

Step-by-Step Check

Application and operating principle support 1, 2 and 4; the “only resistive load” restriction is false. Hence A.

Why the Other Options Are Wrong

Option B is incorrect because it includes incorrect statement(s) 3 and omits correct statement(s) 2, 4. Option C is incorrect because it includes incorrect statement(s) 3 and omits correct statement(s) 1, 4. Option D is incorrect because it includes incorrect statement(s) 3.

Answer-Key Verification Note

The uploaded provisional key marks C . After independent technical verification, the defensible answer is A . This discrepancy is stated explicitly rather than silently copying the provisional key.

Exam Shortcut / Approach

AC controller → same frequency, variable RMS voltage.

Common Mistake

Confusing an AC voltage controller with a frequency converter/inverter.

Quick Revision

RMS Voltage Phase Control and Applications is linked with AC Voltage Controller, AC Controllers and Power Electronics. AC controller → same frequency, variable RMS voltage.