# Basic Electrical Engineering Questions and Answers – Magnetic Field of a Solenoid

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This set of Basic Electrical Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Magnetic Field of a Solenoid”.

1. The magnetic field strength of a solenoid can be increased by inserting which of the following materials as the core?
a) Copper
b) Silver
c) Iron
d) Aluminium

Explanation: The Magnetic field of a solenoid increases when we insert an iron core because iron is a ferromagnetic material and ferromagnetic materials help in increasing the magnetic property.

2. If a coil is wound around a steel core and electric current is passed through the coil, the steel core acts as a?
a) Electromagnet
b) Permanent magnet
c) Neither electromagnet nor permanent magnet
d) Either electromagnet or permanent magnet

Explanation: When a coil is wound around a steel core, the steel core behaves like a permanent magnet because it is a ferromagnetic material and once it becomes magnetic it does not lose its magnetic property.

3. What is the formula for the magnetic field due to a solenoid?
a) μnI
b) μn2
c) μNI
d) μN2I2

Explanation: The magnetic field due to a solenoid is:
B= μnI, where μ is the permeability, n is the number of turns per unit length and I is the current in the solenoid.

4. 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

Explanation: 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.

5. What happens to the magnetic field in the solenoid when the current increases?
a) Increases
b) Decreases
c) Remains constant
d) Becomes zero

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

6. 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

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

7. The current in a solenoid is 30A, the number of turns per unit length is 500 turns per metre. Calculate the magnetic field if the core is air.
a) 18.84T
b) 18.84mT
c) 1.84T
d) 1.84mT

Explanation: The magnetic field in a solenoid is given by:
B=μnI
Substituting the values in the given values in the equation, B=18.84mT.

8. The magnetic field of the solenoid is 18.84mT, the number of turns per unit length is 500 turns per metre. Calculate the current if the core is air.
a) 300A
b) 30A
c) 3A
d) 300mA

Explanation: The magnetic field in a solenoid is given by:
B=μnI
Substituting the values in the given values in the equation, I=30A.

9. The magnetic field of the solenoid is 18.84mT, 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

Explanation: 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.