100 Electromagnetism MCQ with Explanation - Objective Question Answer for Electromagnetism Quiz

41. 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.

42. 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.

43. 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.

44. 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.

45. 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.

46. 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.

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

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

From the expression:

F = Kq₁q₂/r², of Coulomb’s Law

the value of K being 9 × 10⁹,

we get F = 13.5 kN.

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48. If the flow of electric current is parallel to the magnetic field, the force will be?

A. Zero
B. Infinity
C. Maximum
D. Half the original value

Answer: A

Force is a cross-product. A cross product involves the sine of the angle between them. If two quantities are parallel to each other, the angle between them is zero. Sin(0) is zero, hence force is zero.

49. The ratio of magnetic force to electric force on a charged particle getting undeflected in a field is ______

A. 1
B. 0
C. 2
D. 4

Answer: A

When a charged particle is undeflected in a field, the magnitude of the magnetic force and electric force acting on the particle is the same, hence the ratio is 1.

50. Weakest force in nature is __________

A. Electric force
B. Gravitational force
C. Weak force
D. Magnetic force

Answer: B

Gravitational force is the weakest force in nature as it does not bind anything strongly with its help.

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