Question

Which of the following statements is not true for electric energy in ac form compared to that in dc form?

• A. Production of ac is economical.
• B. ac can be easily and efficiently converted from one voltage to the other.
• C. ac can be transmitted economically over long distances.
• D. ac is less dangerous.

Hint:

The three major advantages of AC are:
• Economical generation,
• Easy voltage transformation using transformers,
• Efficient long-distance transmission with low power loss. The statement “AC is less dangerous” is not considered true.

Answer 1

The Correct Option is D

Concept: Alternating current (AC) possesses several practical advantages over direct current (DC), especially in generation, transmission and distribution of electrical energy. However, AC is generally considered more dangerous than DC of the same effective voltage because the continuously changing current can affect the human nervous and muscular systems more severely.

Step 1: Examine statement (A). AC generators are simple in construction and economical for large-scale electricity production. Hence, \[ \boxed{\text{Statement (A) is true.}} \]

Step 2: Examine statement (B). Using transformers, AC voltage can be increased or decreased very efficiently. This is one of the biggest advantages of AC power. Therefore, \[ \boxed{\text{Statement (B) is true.}} \]

Step 3: Examine statement (C). For long-distance transmission, voltage is stepped up. Since \[ P=VI, \] higher voltage implies lower current for the same power. As power loss is \[ P_{\text{loss}}=I^2R, \] the losses become very small. Thus AC transmission is economical. Therefore, \[ \boxed{\text{Statement (C) is true.}} \]

Step 4: Examine statement (D). The statement says: \[ \text{AC is less dangerous.} \] This is incorrect. In practice, AC is generally more dangerous than DC of the same voltage because it can cause severe muscular contractions and interfere with heart rhythms. Hence, \[ \boxed{\text{Statement (D) is not true.}} \]

Step 5: Final conclusion. Among the given statements, only option (D) is incorrect. Therefore, \[ \boxed{\text{(D) ac is less dangerous}} \] is the required answer.