Question

Identify the correct statements among the following.
A. The torque acting on a planar current loop in a magnetic field changes when its shape is changed without changing its area.
B. Two parallel wires carrying currents in opposite directions attract each other.
C. An ideal ammeter has zero resistance and an ideal voltmeter has infinite resistance.
D. A galvanometer can be converted into a voltmeter by connecting a high resistance in series.

Choose the correct answer from the options given below:

• A. A, B and C only
• B. B, C and D only
• C. C and D only
• D. A and C only

Hint:

Torque depends on area, not shape. Opposite currents repel.

Answer 1

The Correct Option is C

Step 1: Recall the facts.
Torque on a loop depends on area, not shape. Like currents attract and unlike currents repel. Ammeters are low resistance and voltmeters are high resistance.

Step 2: Test the statements one by one.
With the same area, the torque \(NIAB\sin\theta\) is unchanged, so A is wrong. Wires with opposite currents repel, so B is wrong. An ideal ammeter has $R=0$ and an ideal voltmeter has $R=\infty$, so C is right. A series resistance \(R_s\) turns a galvanometer into a voltmeter, so D is right.

Step 3: Pick the option.
The set of right statements is {C, D}. This is printed as option 3. The other options each contain A or B, which we showed are false.

Final Answer:
The right statements are C and D, printed as option 3. \[ \boxed{\text{C and D only}} \]