L1 - Magnetism: True Or False

Question 1

Lines of force always emerge from the North Pole

Answer 1

True

Question 2

All magnetism is not the same regardless of it source

Answer 2

False

Gravity is proportional to the source’s mass, magnetism isn’t. Gravity affects everything, magnetism won’t.

Question 3

There is a force of attraction between like magnetic poles

Answer 3

False

identical poles (two north or two south) repel.

opposite poles (north and south) attract.

Question 4

Reluctance of a material is resistance to magnetic flux

Answer 4

True

Resistance opposes the flow of electric current and results in the loss of power in the form heat. Reluctance opposes the flow of magnetic flux, but instead of dissipating it in the form of heat, it stores in the form of magnetic field.

Question 5

Earth’s geographic and magnetic poles are at the same spot

Answer 5

False

A magnetic compass does not point to the geographic north pole. A magnetic compass points to the earth’s magnetic poles, which are not the same as earth’s geographic poles. Furthermore, the magnetic pole near earth’s geographic north pole is actually the south magnetic pole. When it comes to magnets, opposites attract.

Question 6

Permeability is a measure of ability to conduct flux.

Answer 6

True

Permeability is a material property that describes the ease with which a magnetic flux is established in a component. The maximum permeability is the point where the slope of the B/H curve (hysteresis loop) for the unmagnetized material is the greatest.

Question 7

A permanent magnet can be weakened by physical abuse

Answer 7

True

Over a longer period of time, random temperature fluctuations, stray magnetic fields and mechanical movement will cause magnetic properties to decay.

Question 8

The reluctance of iron is much higher than the air

Answer 8

False.

Air and vacuum have high reluctance. Easily magnetized materials such as soft iron have low reluctance.

Question 9

Unlike magnetic poles repels

Answer 9

False

A Magnet attracts or repels other magnets, depending on their mutual orientation of North and South Poles. So, like poles repel and unlike poles attract.

Question 10

Magnetic lines of force are called flux

Answer 10

True

The magnetic lines of force, indicate the region in which the force of the magnet can be detected. This region is called the magnetic field. The magnetic lines of force, or flux, leave the north pole and enter the south pole.

Question 11

The unit of flux is the Weber

Answer 11

True

In physics, the weber (Wb) is the unit of magnetic flux in the International System of Units (SI). The unit is derived (through Faraday’s law of induction) from the relationship 1 Wb = 1 V⋅s (volt-second).

Question 12

One Weber of flux is 10^6 lines

Answer 12

False; 10^8 lines

Many times, the weber is expressed in terms of other derived units as the Tesla-square meter (T·m2), volt-seconds (V·s), or joules per ampere (J/A). 1 Wb = 1 V·s = 1 T·m2 = 1 J/A = 108 Mx (maxwells).

Question 13

High carbon steel has a lower reluctance than soft iron

Answer 13

False

Question 14

Soft iron is most suitable for temporary magnets

Answer 14

True

Soft iron has a low carbon content and is easily magnetised and demagnetised with a small hysteresis loss. For permanent magnets iron alloy Alnico is used.

Question 15

To destroy a magnet, hold it in an AC coil

Answer 15

True

The microscopic atomic magnets in the permanent magnet become disoriented while the current is still running, and the permanent magnet becomes demagnetized.

Question 16

Magnetic field = Magnetic Flux = Lines of force

Answer 16

True

Question 17

Hard steel is better than iron for permanent magnets

Answer 17

True

Steel is one of the materials having high coercivity, That means more energy will be needed to demagnetize steel. So it is an ideal material for making permanent magnets. The case of electromagnets is just the opposite where those materials must have low coercivity and high permeability.

Question 18

A North pole may exist in isolation

Answer 18

False

Magnetic poles always exist in pairs and cannot: exist independently. If a bar magnet is broken into two or more pieces, each of them will have a north pole and a south pole. Hence. It is impossible to obtain a piece of the magnet with only one magnetic pole.

Question 19

Weber’s theory of magnetism refers to electron spin

Answer 19

False.

Weber’s theory, also known as the molecular theory of magnets, states that a magnet can split into an indefinite number of parts. These parts do not lose the properties of magnets and maintain their magnetic poles.

Electron Spin: Theory, Direction, Spin magnetic Moment of Electron, Applications. In 1925, two great scientists, Samuel Goutsmit and G.E. Uhlenbeck proposed that electrons have an inherent angular momentum which is present in the form of magnetic moment of electron and is termed as spin.

Question 20

Magnetic flux cannot travel in a vacuum

Answer 20

True

Vacuum - in electromagnetism, the “vacuum” is a hypothetical medium used to denote lack of any matter, without molecules, atoms or even sub-atomic particles such as electrons. The lack of matter means lack of any magnetic dipole moments which can respond to the applied magnetic field by aligning to it.

Question 21

The best permanent magnets are made of steel alloys

Answer 21

True

In order to create a magnetic field, an object’s atoms must be properly oriented. Steel is highly effective for this purpose because of the natural positioning of its atoms. Steel isn’t the only material used to make permanent magnets.

Question 22

Copper is considered a non-magnetic material

Answer 22

True

While copper atoms do have a single electron in their valence (or outermost) shell, when multiple copper atoms come together, these valence electrons get sent into a cloud which forms metallic bonds between the copper atoms. This makes copper diamagnetic — it repels magnetic fields.

Question 23

A magnet is ‘saturated’ when held under water

Answer 23

False

Since water is almost completely non-magnetic, it just doesn’t make any significant extra magnetic force on the magnets.

Question 24

Magnets (bar) should be stored in pairs

Answer 24

True

Magnets become weaker with time (due to ‘free’ poles) near the ends repelling each other and upsetting alignment of tiny magnets. To prevent this bar magnets are stored in pairs with unlike poles opposite and pieces of soft iron - keepers across the ends.

Question 25

The strength of an electromagnet can be doubled by doubling the AWG size of the wire

Answer 25

True

Thinner wire can decrease the strength of an electromagnet because it has a higher resistance, causing more energy to be lost as heat. Thicker wire, on the other hand, has lower resistance and can handle more current, resulting in a stronger magnetic field.