L1 - Magnetism: True Or False Flashcards
Lines of force always emerge from the North Pole
True
All magnetism is not the same regardless of it source
False
Gravity is proportional to the source’s mass, magnetism isn’t. Gravity affects everything, magnetism won’t.
There is a force of attraction between like magnetic poles
False
identical poles (two north or two south) repel.
opposite poles (north and south) attract.
Reluctance of a material is resistance to magnetic flux
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.
Earth’s geographic and magnetic poles are at the same spot
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.
Permeability is a measure of ability to conduct flux.
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.
A permanent magnet can be weakened by physical abuse
True
Over a longer period of time, random temperature fluctuations, stray magnetic fields and mechanical movement will cause magnetic properties to decay.
The reluctance of iron is much higher than the air
False.
Air and vacuum have high reluctance. Easily magnetized materials such as soft iron have low reluctance.
Unlike magnetic poles repels
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.
Magnetic lines of force are called flux
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.
The unit of flux is the Weber
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).
One Weber of flux is 10^6 lines
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).
High carbon steel has a lower reluctance than soft iron
False
Soft iron is most suitable for temporary magnets
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.
To destroy a magnet, hold it in an AC coil
True
The microscopic atomic magnets in the permanent magnet become disoriented while the current is still running, and the permanent magnet becomes demagnetized.
Magnetic field = Magnetic Flux = Lines of force
True
Hard steel is better than iron for permanent magnets
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.
A North pole may exist in isolation
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.
Weber’s theory of magnetism refers to electron spin
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.
Magnetic flux cannot travel in a vacuum
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.
The best permanent magnets are made of steel alloys
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.
Copper is considered a non-magnetic material
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.
A magnet is ‘saturated’ when held under water
False
Since water is almost completely non-magnetic, it just doesn’t make any significant extra magnetic force on the magnets.
Magnets (bar) should be stored in pairs
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.
The strength of an electromagnet can be doubled by doubling the AWG size of the wire
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.
