# Basic Electrical Engineering Questions and Answers – Factors Determining the Inductance of a Coil

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This set of Basic Electrical Engineering online test focuses on “Factors Determining the Inductance of a Coil”.

1. As the number of turns in the coil increases, what happens to the inductance of the coil?
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero

Explanation: Inductance is directly proportional to the square of the number of turns in the coil, hence as the number of turns increases, inductance also increases.

2. What happens to the inductance when the magnetic field strength decreases?
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero

Explanation: Inductance is directly proportional to the magnetic field strength in the coil, hence as the magnetic field strength decreases, inductance decreases.

3. What happens to the inductance when the current in the coil becomes double its original value?
a) Becomes half
b) Becomes four times
c) Becomes double
d) Remains same

Explanation: ϕ is directly proportional to i.
Φ=Li where L is constant of proportionality
So, when current get double ϕ also becomes double keeping L same.
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4. When the coil is wrapped around a ferromagnetic core, why is it difficult to determine the inductance?
a) The variation of flux is no longer proportional to the variation of current
b) Current does not exist in the coil
c) Flux does not exist in the coil
d) The value of current is too large to measure

Explanation: When a coil is wrapped around a ferromagnetic core, it is difficult to determine the inductance because the variation of flux is no longer proportional to the variation of the current.

5. What happens to the inductance as the area of the cross section of the coil increases?
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero

Explanation: L=µ0*N2*A/l, hence as the area of cross section A increases, the inductance also increases.
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6. What happens to the inductance as the length of the magnetic circuit increases?
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero

Explanation: L=µ0*N2*A/l, hence as the length of the magnetic circuit l increases, the inductance decreases.

7. If the current changes from 20A to 10A in 5 seconds and the value of inductance is 1H, calculate the emf induced.
a) 8V
b) 6V
c) 4V
d) 2V

Explanation: We know that:
emf=L(i2-i1)/t
Substituting the values from the question we get emf=2V.

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