Magnetism And Matter Flashcards
The word magnet is derived from the
Name of island in Greece called Magnesia.
Some of the commonly non-ideas regarding magnetism are: -
- the Earth behaves as a magnet with the magnetic field appointing approximately from the geographic south to the north.
- when a bar magnet is freely, suspended, it points in the north south direction. The tip which points to the geographical north is called north pole and the tip which points to the geographical south is called south of the magnet.
- there is a repulsive force when north poles or south poles of magnets are brought close together. Conversely, there is an attractive force between the north pole of one magnet and the south pole of the other.
- we cannot isolate the north, or south pole of a magnet. If a bar magnet is broken into 2 halves, we get two similar by markets with somewhat weaker properties. Unlike electric charges, isolated, magnetic north and south poles are known as magnetic monopoles do not exist.
- it is possible to make magnets out of iron and its alloys.
What allows us to plot magnetic field lines?
The pattern of iron filings permit us to plot magnetic field lines.
Define magnetic field lines.
The magnetic field lines are a visual and intuitive realization of the magnetic field.
Properties of magnetic field lines
- the magnetic field lines of a magnet firm, continuous closed loops.
- the tangent to the field line at a given point represents direction of the net magnetic field be at that point.
- the larger the number of reliance crossing per unit area, the stronger is the magnitude of magnetic field.
- the magnetic field lines do not intersect for if they did the direction of magnetic field would not be unique at that point of intersection.
A bar magnet and a solenoid produces similar magnetic field. Justify.
- The assemblance of magnetic field lines for a bad magnet, and a solid suggest that a magnetic can be taught as a large number of circulating current in analogy with a solenoid.
- cutting a magnet in half is like cutting a solid. We get two smaller solids with weaker magnetic properties.
- the field lines remain continuous, emerging from one phase of the solid and entering into the other face.
- the magnetic moment of a bomb magnet is equal to the magnetic moment of an equivalence solenoid that produces the same magnetic field.
Max pe
-mB
Theta = 0
Min pe
+mB
Theta = 180
What happens if a bar magnet is cut into two pieces: (i) transverse to Its length. (ii) along its length?
In either case, one gets two magnets, each with a north and south pole.
A magnetised needle in a uniform magnetic field experiences a torque but no net force. An iron nail near a bar magnet, however. experiences a force of attraction in addition to a torque. Why?
No force if the field is uniform. The iron nail experiences a non-uniform field due to the bar magnet. There is induced magnetic moment in the nail, therefore, it experiences both force and torque. The net force is attractive because the induced south pole (say) in the nail is closer to the north pole of magnet than induced north pole.
A magnetised needle in a uniform magnetic field experiences a torque but no net force. An iron nail near a bar magnet, however. experiences a force of attraction in addition to a torque. Why?
No force if the field is uniform. The iron nail experiences a non-uniform field due to the bar magnet. There is induced magnetic moment in the nail, therefore, it experiences both force and torque. The net force is attractive because the induced south pole (say) in the nail is closer to the north pole of magnet than induced north pole.
Must every magnetic configuration have a north pole and a south
pole? What about the field due to a toroid?
Not necessarily. True only if the source of the field has a net non-zero magnetic moment. This’is not so for a toroid or even for a straight infinite conductor.
Two identical looking iron bars A and B are given, one of which is definitely known to be magnetised. (We do not know which one.) How would one ascertain whether or not both are magnetised? If only one is magnetised, how does one ascertain which one? [Use nothing else but the bars A and B.]
Try to bring different ends of the bars closer. A repulsive force in some situation establishes that both are magnetised. If it is always attractive, then one of them is not magnetised. In a bar magnet the intensity of the magnetic field is the strongest at the two ends (poles) and weakest at the central region. This fact may be used to determine whether A or B is the magnet. In this case, to see which one of the two bars is a magnet, pick up one, (say, A) and lower one of its ends; first on one of the ends of the other (say, B), and then on the middle of B. If you notice that in the middle of B. A experiénces no force, then B is magnetised. If you do not notice any change from the end to the middle of B. then A is magnetised.
