# Physics Questions and Answers – Electromagnetic Induction – Magnetic Flux

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This set of Physics Multiple Choice Questions & Answers (MCQs) focuses on “Electromagnetic Induction – Magnetic Flux”.

1. Pick out the SI unit of magnetic flux.
a) Ampere
b) Tesla meter
c) Weber
d) Maxwell

Explanation: The magnetic flux through a surface is the surface integral of the normal component of the magnetic field flux density passing through that surface. The SI unit of magnetic flux is weber (Wb). One weber is the flux produced when a uniform magnetic field of one tesla acts normally over an area of 1 cm2.

2. Identify the correct dimensions of magnetic flux.
a) [M3 L2 A-1 T-2]
b) [M L2 A-1 T-2]
c) [M2 L2 A-1 T-2]
d) [M L2 A-1 T2]

Explanation: Magnetic flux = Magnetic field × Area.
Flux = $$\frac { ( [ M L T^{-2} ].[ L^2 ])}{(A L) }$$
Flux = $$\frac { [M L^2 T^{-2} ] }{ [ A ] }$$
Flux = [M L2 A-1 T-2].

3. Which of the following is a unit of magnetic flux?
a) Maxwell
b) Gauss
c) Tesla
d) Ampere

Explanation: The CGS unit of magnetic flux is Maxwell (Mx). One Maxwell is the flux produced when a uniform magnetic field of one gauss acts normally over an area of 1 cm2.
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4. Find out the correct relation from the following.
a) 1 Wb = 1 G cm
b) 1 Wb = 1 Tm
c) 1 Wb = 1 G cm2
d) 1 Wb = 108 Maxwell

Explanation: 1 Wb = 1 T × 1 m2
Wb = 104 G × 104 cm2.
1 Wb = 108 Maxwell.

5. When is the magnetic flux said to be positive?
a) θ = 180o
b) θ = 360o
c) θ = 0o
d) θ = 90o

Explanation: A normal to a plane can be drawn from either side. If the normal drawn to a plane points out in the direction of the field, then θ = 0o and the flux are taken as positive. If the flux is positive and increasing the voltage will be negative.

6. The total number of magnetic lines of force crossing the surface placed in a magnetic field normally is called the magnetic induction.
a) True
b) False

Explanation: The magnetic flux through any surface place in a magnetic field is the total number of magnetic lines of force crossing this surface normally. It is measured as the product of the component of the magnetic field normal to the surface and the surface area.

7. Calculate the magnetic flux when the magnetic field is perpendicular to the surface area.
a) Minimum
b) Maximum
c) Zero
d) Depends on the surface area

Explanation: Magnetic flux = B ΔS cos 00
Magnetic flux = B ΔS.
It follows that magnetic flux linked with a surface is maximum when the direction of the magnetic field is perpendicular to the surface area.

8. Which type of physical quantity is magnetic flux?
a) Scalar
b) Vector
c) Isotropic
d) Isentropic

Explanation: The magnetic flux is measured as the product of the component of the magnetic field normal to the surface and the surface area.
Magnetic flux is a scalar quantity.

9. Calculate the magnetic flux produced when the magnetic field is parallel to the surface area.
a) Maximum
b) Minimum
c) Zero
d) Depends on the magnetic field

Explanation: Magnetic flux = B ΔS cos 90o
Magnetic flux = 0.
It follows that magnetic flux linked with a surface is zero when the direction of the magnetic field is parallel to the surface area.

10. When is the magnetic flux said to be negative?
a) θ = 180o
b) θ = 360o
c) θ = 90o
d) θ = 0o

Explanation: If the normal points in the opposite direction of the field, then θ = 180o and the flux is taken as negative. If the magnetic field is pointing opposite the direction of the surface area then the value of this flux is negative.

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