# Basic Electrical Engineering Questions and Answers – Magnetomotive Force and Magnetic Field Strength

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This set of Basic Electrical Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Magnetomotive Force and Magnetic Field Strength”.

1. What is a permeable substance?
a) Any good conductor
c) Any strong magnet
d) Any substance through which the magnetic lines of force can pass easily

Explanation: A permeable substance is one through which the magnetic lines of force can pass easily.

2. Materials having good retentivity are?
a) Strong magnets
b) Weak magnets
c) Temporary magnets
d) Permanent magnets

Explanation: Materials with good retentivity are permanent magnets because they can retain magnetism even when no external magnetic field present.

3. Magnetic field exists along which of the following?
a) Moving charges
b) Stationary charges
c) Copper
d) Iron

Explanation: Moving charges have a magnetic field associated with them because they have magnetic flux lines associated with it.
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4. Magnetomotive force is equal to__________________
a) current * number of turns
b) current / number of turns
c) current / number of turns per unit length
d) current * number of turns per unit length

Explanation: MMF is ability to produce flux and is equal to product of current flowing and number of turns.

5. Unit of MMF is ______________
a) A/m
b) A-m
c) A
d) unitless

Explanation: MMF is equal to the product of current flowing and number of turns.
unit of Magnetomotive force = unit of current = A or ampere.

6. When a bar magnet is broken into two pieces, which of the following are true?
a) The magnet loses its magnetism
b) The magnet has only north pole left
c) The magnet has only south pole left
d) The magnet turns into two new bar magnets

Explanation: When a bar magnet is broken into two pieces, it forms two different bar magnets. This happens because the broken pieces of the magnet form a separate north and south pole for itself as monopoles do not exist.

7. When an electric current flows into the page, what is the direction of the magnetic field?
a) Clockwise
b) Anti-clockwise
c) Cannot be determined
d) Parallel to the current

Explanation: When the current flows into the page, the magnetic field is clockwise because of the right hand thumb rule, we orient our thumb into the page and our fingers curl in the clockwise direction.

8. When an electric current flows out of the page, what is the direction of the magnetic field?
a) Clockwise
b) Anti-clockwise
c) Cannot be determined
d) Parallel to the current

Explanation: When the current flows out of the page, the magnetic field is anti-clockwise because of the right hand thumb rule, we orient our thumb out of the page and our fingers curl in the anti-clockwise direction.

9. The relation between the direction of current and the direction of magnetic field is?
a) Same direction
b) Opposite direction
c) Perpendicular
d) Unrelated

Explanation: When a conductor carries a certain value of current, the force developed in the conductor, the current in the conductor and the magnetic field in the conductor are mutually perpendicular to each other.