Magnetic Field Due to Electric Current MCQ [Free PDF] - Objective Question Answer for Magnetic Field Due to Electric Current Quiz

11. What happens to the magnetic field in the solenoid when the number of turns increases?

A. Increases
B. Decreases
C. Remains constant
D. Becomes zero

Answer: A

The magnetic field of a solenoid is directly proportional to the number of turns in it. Hence as the number of turns increases, the magnetic field also increases.

12. What happens to the magnetic field in the solenoid when the current increases?

A. Increases
B. Decreases
C. Remains constant
D. Becomes zero

Answer: A

The magnetic field of a solenoid is directly proportional to the current in it. Hence as the current increases, the magnetic field also increases.

13. What happens to the magnetic field in the solenoid when the length of the solenoid increases?

A. Increases
B. Decreases
C. Remains constant
D. Becomes zero

Answer: B

The magnetic field of a solenoid is inversely proportional to the length. Hence as the length increases, the magnetic field decreases.

14. The current in a solenoid is 30A, and the number of turns per unit length is 500 turns per meter. Calculate the magnetic field if the core is air.

A. 18.84T
B. 18.84mT
C. 1.84T
D. 1.84mT

Answer: B

The magnetic field in a solenoid is given by:

B = μnI

Substituting the values in the given values in the equation,

B = 18.84mT.

15. The magnetic field of the solenoid is 18.84mT, and the number of turns per unit length is 500 turns per meter. Calculate the current if the core is air.

A. 300A
B. 30A
C. 3A
D. 300mA

Answer: B

The magnetic field in a solenoid is given by:

B = μnI

Substituting the values in the given values in the equation, I = 30A.

16. The magnetic field of the solenoid is 18.84mT, and the current is 30A. Calculate the number of turns per unit length if the core is air.

A. 1500 turns/m
B. 1000 turns/m
C. 500 turns /m
D. 2000 turns/m

Answer: C

The magnetic field in a solenoid is given by:

B = μnI

Substituting the values in the given values in the equation n = 500 turns/m.

17. What is the expression for force in a current-carrying conductor?

A. F = K/r²
B. F = Kq/r²
C. F = Kq₁q₂/r²
D. F = Kq₁q₂/r

Answer: C

The force in a current-carrying conductor is directly proportional to the product of the two charges and inversely proportional to the square of the distance between them.

Hence F = Kq₁q₂/r²,

where K is the constant of proportionality.

18. Force in a conductor is__________ to the product of the charges.

A. Directly proportional
B. Inversely proportional
C. Not related
D. Cannot be determined

Answer: A

The force in a current-carrying conductor is directly proportional to the product of the two charges and inversely proportional to the square of the distance between them.

19. Force in a conductor is __________ to the square of the distance between the charges.

A. Directly proportional
B. Inversely proportional
C. Not related
D. Cannot be determined

Answer: B

The force in a current-carrying conductor is directly proportional to the product of the two charges and inversely proportional to the square of the distance between them.

20. Calculate the force between two charges having magnitude 3nC and 2nC separated by a distance of 2micro m.

A. 13.5N
B. 13.5kN
C. 1.35N
D. 1.35kN

From the expression:

F = Kq₁q₂/r², of Coulomb’s Law

the value of K being 9 × 10⁹,

we get F = 13.5kN.

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