Quick Review Flashcards - Click to flip and test your knowledge!
Question
What is the chemical name and formula for the ore known as lodestone?
Answer
It is an ore of iron oxide with the formula $Fe_{3}O_{4}$.
Question
Where was the first known natural magnet, lodestone, found in large quantities?
Answer
It was found in Magnesia, in Asia Minor.
Question
What are the two primary properties observed in lodestone?
Answer
It attracts small pieces of iron and sets itself in a definite direction when suspended freely.
Question
Which civilization is credited with using lodestone to guide boats earlier than 2500 B.C.?
Answer
The Chinese.
Question
Why are artificial magnets prepared despite the existence of natural magnets?
Answer
Natural magnets are irregularly shaped and are not magnetically strong enough for practical use.
Question
In which geographic direction does a freely suspended magnet always point?
Answer
It always points in the geographic north-south direction.
Question
How are the two poles of a magnet named based on their resting direction?
Answer
The end pointing north is the north pole, and the end pointing south is the south pole.
Question
What is the fundamental law of magnetic poles regarding attraction and repulsion?
Answer
Like poles repel each other, while unlike poles attract each other.
Question
Define the term 'induced magnetism'.
Answer
It is the temporary magnetism acquired by a magnetic material when it is kept near or in contact with a magnet.
Question
Which type of polarity is developed at the 'near end' of a magnetic material during induction?
Answer
An opposite polarity to that of the magnet pole near it.
Question
Which type of polarity is developed at the 'farther end' of a magnetic material during induction?
Answer
A similar polarity to that of the inducing magnet pole near the other end.
Question
What happens to the magnetism of a soft iron bar once the inducing magnet is removed?
Answer
The bar loses its magnetism, meaning the induced magnetism is purely temporary.
Question
Explain why an ordinary piece of iron is attracted towards a magnet.
Answer
The iron first becomes a magnet by induction, and then the opposite poles attract.
Question
The phenomenon where induction must occur before a magnet can pull an object is summarised by the phrase _____.
Answer
Induction precedes attraction.
Question
How is a 'chain of nails' formed when one nail is attached to a magnet?
Answer
The magnet magnetises the first nail by induction, which then magnetises the next nail in the same manner.
Question
What is the 'magnetic field' of a magnet?
Answer
The region around a magnet in which a magnetic needle or compass gets influenced.
Question
How does the strength of a magnetic field change as the distance from the magnet increases?
Answer
The effect of the magnetic field decreases as the distance increases.
Question
Is magnetic field a scalar or a vector quantity?
Answer
It is a vector quantity.
Question
How is the magnitude of a magnetic field at a point measured?
Answer
By the force experienced by a magnetic pole of unit strength placed at that point.
Question
What determines the direction of the magnetic field at any given point?
Answer
The direction in which the north pole of a magnetic compass needle rests when placed at that point.
Question
Define 'magnetic field lines'.
Answer
Continuous curves in a magnetic field such that the tangent at any point gives the direction of the magnetic field.
Question
In what direction do magnetic field lines travel 'outside' the magnet?
Answer
They are directed from the north pole towards the south pole.
Question
In what direction do magnetic field lines travel 'inside' the magnet?
Answer
They are directed from the south pole towards the north pole.
Question
What is indicated by the tangent at any point on a magnetic field line?
Answer
The direction of the magnetic field at that specific point.
Question
Why can two magnetic field lines never intersect?
Answer
Intersection would imply two different directions of the magnetic field at the same point, which is impossible.
Question
What does the density or 'crowding' of magnetic field lines represent?
Answer
It represents the strength of the magnetic field; crowded lines indicate a strong field.
Question
Where are magnetic field lines most crowded in a bar magnet?
Answer
Near the poles of the magnet.
Question
What type of magnetic field is represented by parallel and equidistant field lines?
Answer
A uniform magnetic field.
Question
What physical behaviour do magnetic field lines mimic according to their properties?
Answer
They behave like stretched elastic rubber strings.
Question
What happens to an iron rod buried deep inside the Earth in a north-south direction?
Answer
It eventually becomes a weak magnet.
Question
What are 'neutral points' in the context of magnetic field plotting?
Answer
Points where the resultant magnetic field is zero because the magnet's field is neutralised by Earth's field.
Question
How does a magnetic compass behave when placed at a neutral point?
Answer
It can rest in any direction because the net magnetic force is zero.
Question
Define 'earth's magnetic poles'.
Answer
The two places on the Earth's surface where a magnetic needle becomes vertical.
Question
Define the 'magnetic equator'.
Answer
The imaginary line joining places where a magnetic needle remains horizontal.
Question
What is the approximate angle between the Earth's magnetic axis and its axis of rotation?
Answer
Approximately $17^{\circ}$.
Question
Where is the Earth's magnetic south pole currently located geographically?
Answer
In Canada, at approximately $70$-$75^{\circ}$ North latitude and $96^{\circ}$ West longitude.
Question
Where is the Earth's magnetic north pole currently located geographically?
Answer
Near the geographic south pole at $73^{\circ}$ South latitude and $155^{\circ}$ East longitude.
Question
Do the Earth's magnetic poles remain in a stationary position over long periods?
Answer
No, they gradually change their positions over time.
Question
In a limited space, how are the magnetic field lines of the Earth described?
Answer
They are parallel and equidistant to each other.
Question
What is the direction of Earth's uniform magnetic field lines relative to geographic directions?
Answer
They are directed from geographic south to geographic north.
Question
When plotting field lines for a bar magnet with its north pole facing geographic north, where are the neutral points located?
Answer
On either side of the magnet in the east-west direction (broad side-on position).
Question
When plotting field lines for a bar magnet with its south pole facing geographic north, where are the neutral points located?
Answer
On either side of the magnet in the north-south direction (end-on position).
Question
What two magnetic fields are equal and opposite at a neutral point?
Answer
The magnetic field produced by the magnet and the horizontal component of the Earth's magnetic field.
Question
Describe the magnetic field lines produced by a horse shoe magnet.
Answer
They are curved, non-equispaced, and non-parallel (non-uniform).
Question
How can you test if a rod is made of iron or copper using a magnet?
Answer
An iron rod will get magnetised by induction and be attracted, whereas a copper rod will not.
Question
In the experiment to plot Earth's magnetic field, why are brass pins used to fix the paper?
Answer
Brass is a non-magnetic material and will not interfere with the magnetic compass needle.
Question
What is the net magnetic field magnitude at a neutral point?
Answer
Zero.
Question
At which geographic location is the Earth's magnetic field directed vertically upwards?
Answer
At the Earth's magnetic north pole (located near the geographic south pole).
Question
At which geographic location is the Earth's magnetic field directed vertically downwards?
Answer
At the Earth's magnetic south pole (located near the geographic north pole).
Question
Why do iron filings arrange themselves in curved lines when sprinkled over a bar magnet?
Answer
Each filing becomes magnetised by induction and experiences a force that aligns it with the magnetic field lines.
Question
What is the horizontal component direction of Earth's magnetic field?
Answer
From geographic south to geographic north.
Question
If two magnets are placed with like poles facing each other, where is the neutral point located?
Answer
At a point exactly midway between the two magnets.
Question
True or False: The magnetic field lines of Earth are normal to the Earth's surface near the magnetic poles.
Answer
True.
Question
What is the orientation of Earth's magnetic field lines relative to the surface at the magnetic equator?
Answer
They are parallel to the Earth's surface.
Question
How can you mark the polarity of an unmarked magnet using a magnetic compass?
Answer
The end that repels the north pole of the compass is the north pole; the end that attracts it is the south pole.
Question
Why do two iron pins hung from the same pole of a magnet move apart at their pointed ends?
Answer
The pointed ends acquire similar polarities by induction and repel each other.
Question
Under what condition will the neutral point be on the vertical line away from the north pole?
Answer
When a magnet is standing vertical with its north pole up.
Question
What defines the 'end-on position' for neutral points?
Answer
Points located on the axis of the magnet in the north-south direction.
Question
What defines the 'broad side-on position' for neutral points?
Answer
Points located on the equatorial line of the magnet in the east-west direction.
Question
Why does a compass needle point in any direction at a neutral point?
Answer
Because the magnetic field of the magnet is exactly balanced by the Earth's magnetic field, leaving no resultant force.