This set of Physics Multiple Choice Questions & Answers (MCQs) focuses on “Kirchoff’s Law”.

1. Which among the following is true?

a) According to Kirchhoff’s law, the current flowing towards a junction is equal to the voltage drop

b) According to Kirchhoff’s law, the current flowing towards a junction is equal to the resistance across the junction

c) According to Kirchhoff’s law, the current flowing towards a junction is equal to the current leaving the junction

d) According to Kirchhoff’s law, the current flowing towards a junction is equal to all the currents in the circuit

View Answer

Explanation: According to Kirchhoff’s first law, the current flowing towards the junction is equal to the current leaving the junction. Mathematically, this law can be expressed as ∑

^{n}

_{K – 1}I

_{K}= 0 (where n is the number of branches carrying current towards or away from the junction)

2. The equation → ∑e = ∑IR is applicable to which law?

a) Kirchhoff’s second law

b) Kirchhoff’s junction rule

c) Kirchhoff’s third law

d) Newton’s Law

View Answer

Explanation: The equation → ∑e = ∑IR is applicable to Kirchhoff’s second law. This law is also known as Kirchhoff’s loop rule. This expression tells us that in a closed loop, the algebraic sum of the emfs is equal to the algebraic sum of the products of the resistance and currents flowing through them.

3. Identify the correct statement from the following.

a) While traversing in a closed loop, if negative pole of cell is encountered first, then the emf is negative

b) The product of resistance and current in an arm is taken to be positive if the direction of current is opposite to the direction in which one moves along the closed loop

c) Current flowing away from a junction is taken as positive

d) While traversing in a closed loop, if positive pole of cell is encountered first, then the emf is positive

View Answer

Explanation: According to sign convention while traversing a closed loop (in clockwise or anti-clockwise direction), if positive pole of the cell is encountered first then its emf is negative or else, it will be positive.

4. Kirchhoff’s first law supports law of conservation of charge.

a) True

b) False

View Answer

Explanation: Kirchhoff’s first law or Kirchhoff’s junction law supports law of conservation of charge. According to this law, whatever charges are passing towards the junction is equal to the charges leaving the junction. As a result, the charges are conserved, thereby, supporting the law of conservation of charge.

5. Calculate the value of current I_{4}.

a) -9A

b) 9A

c) 5A

d) 1A

View Answer

Explanation: Current I

_{4}can be calculated using Kirchhoff’s first law. The sum of current arriving at a junction is equal to the currents leaving the junction.

Here, Currents arriving at a junction: 7A + 5A = 12A

Currents leaving the junction: 3A + I

_{4}

Equating both the currents: 12A = 3A + I

_{4}

I

_{4}= 9A

6. In the circuit shown below, calculate the current flowing through 20V cell.

a) 12A

b) 15A

c) 12.5A

d) 12.3A

View Answer

Explanation: Here, we can apply Kirchhoff’s loop rule in closed loops ADCBA, AEFBA, AHGBA, and AIJBA. Thus, we get

20 + 10 – 5I

_{1}= 0 → I

_{1}= 6A

-5 + 20 – 15I

_{2}= 0 → I

_{2}= 1A

25 + 20 – 10I

_{3}= 0 → I

_{3}= 4.5A

-15 + 20 – 5I

_{4}= 0 → I

_{4}= 1A

Therefore, the current flowing through the 20V cell = 6 + 1 + 4.5 + 1 = 12.5A

7. The diagram below shows a network of 5 branches. Given: I_{1} = -5A; I_{4} = 10A; I_{5} = 15A

a) I_{2} = -15A; I_{3} = -5A; I_{6} = -15A

b) I_{2} = 15A; I_{3} = 5A; I_{6} = -15A

c) I_{2} = -15A; I_{3} = -5A; I_{6} = 15A

d) I_{2} = 15A; I_{3} = 5A; I_{6} = 15A

View Answer

Explanation: Given: I

_{1}= -5A; I

_{4}= 10A; I

_{5}= 15A

Applying Kirchhoff’s Laws

At junction D:

I

_{1}+ I

_{2}= I

_{4}→ -5 + I

_{2}= 10 → I

_{2}= 15A

At junction A:

I

_{3}+ I

_{4}= I

_{5}→ I

_{3}+ 10 = 15 → I

_{3}= 5A

I

_{6}= I

_{5}= 15A (Since they are in series)

8. Kirchhoff’s laws are applicable in the presence of magnetic field.

a) True

b) False

View Answer

Explanation: Kirchhoff’s law are not applicable in the presence of a magnetic field. This is because, Kirchhoff’s law is based on the assumption that magnetic fields do not exist in closed loops. Therefore, this law cannot be used when there are time varying magnetic fields.

9. Which among the following can be used to analyze circuits?

a) Kirchhoff’s Law

b) Newton’s Law

c) Coulomb’s Law

d) Stephan’s Law

View Answer

Explanation: Kirchhoff’s Law is used to analyze circuits. This law is important because they represent connections of a circuit. Kirchhoff’s Law provide the constraints that let us find the current flowing and voltage across every circuit element.

10. Find the false statement.

a) Sum of voltage over any closed loop is zero

b) Kirchhoff’s Laws can be applied to any circuit, regardless of its structure and composition

c) Kirchhoff’s 2^{nd} law is applied at nodes

d) Kirchhoff’s 1^{st} law can be applied for both planar and non-planar circuits

View Answer

Explanation: Kirchhoff’s 2

^{nd}year is applied in a closed loop. Kirchhoff’s 2

^{nd}law supports the law of conservation of energy. This means that energy is neither created nor destroyed in the closed loop. Whatever energy enters the loop, same amount leaves the loop.

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