MCQEasyJEE 2024Kirchhoff's Laws & Circuits

JEE Physics 2024 Question with Solution

Three voltmeters are joined as shown. When a potential difference is applied across AA and BB, their readings are V1V_1, V2V_2, and V3V_3. Choose the correct option:

  • A

    V1=V2V_1 = V_2

  • B

    V1=V3V2V_1 = V_3 - V_2

  • C

    V1+V2>V3V_1 + V_2 > V_3

  • D

    V1+V2=V3V_1 + V_2 = V_3

Answer

Correct answer:D

Step-by-step solution

Standard Method

Given: Three voltmeters have readings V1V_1, V2V_2 and V3V_3 between points AA and BB.

Find: The correct relation among V1V_1, V2V_2 and V3V_3.

The solution uses Kirchhoff’s Voltage Law. The total potential difference across the complete path from AA to BB equals the sum of the potential differences across the parts.

So,

V1+V2V3=0V_1 + V_2 - V_3 = 0

Hence,

V1+V2=V3V_1 + V_2 = V_3

Therefore, the correct option is D.

Approach from potential difference measurement

Given: Voltmeters V1V_1, V2V_2 and V3V_3 are connected between points in the shown arrangement.

Find: Which option correctly relates their readings.

A voltmeter measures the potential difference between two points. In this arrangement, V3V_3 measures the total potential difference across AA and BB, while V1V_1 and V2V_2 measure the two parts whose sum gives the total drop.

Therefore,

V3=V1+V2V_3 = V_1 + V_2

So the required relation is

V1+V2=V3V_1 + V_2 = V_3

Thus, the correct answer is V1+V2=V3V_1 + V_2 = V_3, which is option D.

Common mistakes

  • Assuming V1=V2V_1 = V_2 only because both are voltmeters. This is wrong because equality of readings depends on the points across which they are connected, not on the instrument type. Always identify the exact potential difference each voltmeter measures.

  • Ignoring Kirchhoff’s Voltage Law for the complete path. This leads to comparing partial drops directly with the total drop incorrectly. Instead, add the relevant potential differences algebraically around the loop.

  • Treating V3V_3 as one of the partial drops rather than the total potential difference across AA and BB. This gives incorrect relations such as V1+V2>V3V_1 + V_2 > V_3. First decide which meter reads the total applied voltage.

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