Chp 13- Magnetic Effects Of Electric Current Flashcards
What is the SI unit of ‘Magnetic field strength’ and who is it named after?
Strength of magnetic field is measured in the terms of physical quantity called magnetic field induction or magnetic flux density. It is the noted by the B n it’s SI unit is tesla
Unit- Oersted (CGS)
Scientist- Hans Christian Oersted
Define magnet, poles, magnetic field and magnetic field lines, solenoid, electromagnet
•A solid any shape or size which can attract pieces of material like iron, cobalt, nickel is called magnet
•The place where the attracting power of a bar magnet is maximum is called Pole. Poles r regions /small areas and not point.
•The three dimensional region surrounding a magnet dipole in which the force of the magnet can be detected by another magnent/ electromagnetic objects/ current carrying conductor is magnetic field.
• The imaginary path or a line along which the North Pole moves in the magnetic field and iron filing align themselves is called magnetic field lines.
-A solenoid is a long insulation wire wound in the form of a circular helix where neighboring turns are closely spaced.
-electromagnet- a magnet consisting of a soft iron coe with a coil of insulated wire wound around it is called electromanget. Alloy of nickel, iron and copper are also used.
True or false-
Magnetic field is a scalar quantity
False- Magnetic field is a quantity that has both direction and magnitude and thus is a vector quantity
define uniform magnetic field
The magnitude as well as the direction of magnetic field at constant such a field is called uniform magnetic field
True or false-
The far are the field lines, the strong is the magnetic field
False - The relative strength of a magnetic field as shown by the degree of closeness of the field lines
True or false
No two field lines are found to cross each other
True
,Reason - Tangent drawn at any point on the magnetic field gives the direction of the magnetic field. So if the magnetic field lines intersect each other, so it would mean that at the point of the intersection the compass needle point at two different directions which is actually not possible
On what factors does the magnetic effect of electric current depend on?
• Current
The magnitude of the magnetic field produced at a given point increases as the current through the wire increases.
• Distance
Magnetic field produced by a given current in the conductor decreases as the distance from it increases
It can be noted that the concentric circle field around a current carrying straight wire becomes larger and larger as the move away from it
What does
1) Maxwell’s corkscrew rule indicate
2) flemings left hand rule
Maxwell’s corkscrew rule is also called Right Hand thumb rule And it indicates the direction of the magnetic field
2)direction of force on current carrying conductor.(thumb force, Fore finger: Field, Central fingrer:C urrent)
How do magnetic field lines look like in a circular loop?
the direction of magnetic field inside the solenoid id parallel to length of solenoid. at the ends of solenoid,the strength of MF that in the middle of solenoid. A circular loop is made up of many tiny straight wires. And each section of a current carrying wire contribute in the production of magnetic field. Ina circular loop every point on the wire carrying current would give rise to a magnetic field. And these concentric circles representing the magnetic field around it what become larger and larger as we move away from the wire. At the centre of the loop the field lines become straight and perpendicular to the plane of the coil.
On what factors does the Magnetic field due to the current in a circular loop depends on
The magnetic field around a straight current carrying wire can we increase the pending it into a circular loop.
Factors: 1) Amount of current flowing
• If the current increases the deflection of the magnetic compass also increases
Directly proportional
2) Radius of the circular wire
• strength of the magnetic field is inversely proportional to the radius of the circular wire
• The deflection of the needle of the magnetic compass is kept at the centre of circular loop with smaller radius is more than that of the circular loop with big radius
3) Number of turns in the circular loop
• If the no. Of turns per unit length in a circular loop is increased then the magnetic field also increases. the more tightly the turns are wound, stronger will be the magnetic field .
True. Or false -
If there is a circular coil. having N turns then the magnetic field produced is N times as small asproduced by the single turn
False. LARGE by N times
Reason - This is because the current in it circular turn has the same direction and field due to each turn then just adds up
What are the properties of bar magnet
-•Attractive nature-when Iron filing is put near a bar magnet, the magnet attracts the iron filing feeling towards it. The attracting power is maximum near the ends and minimum at the centre.
-•Directive nature- When a magnet is suspended freeely it align itself to north south direction
The pole of the bar magnet pointing towards north direction when suspended freely is called north o ke. The pole of the bar magnet pointing toward south direction when suspended freely is called south pole .
-• Poles-exist in pairs- in bar magnet there are always two poles which are of equal strength and opposite nature. this also means that magnetic mono poles do not exist.
-• Like poles repel unlike poles attract.
-• Inductive nature- Hen certain substances like soft iron, steel , cobalt, nickel are placed near a bar magnet, they acquire magnetisation a called induced magnetisation. The phenomena is called magnetic induction.
What are natural and artificial magnets
Natural magnets are the naturally occurring minerals or ores having magnetic power. Due to irregular shape and weak attractive in power, natural magnets like lodestone are nowadays rarely used.
Artificial magnets - nowadays pieces of iron and many other materials of suitable shapes and sizes are made as magnets by passing current through wire wound around them. Such magnets are called artificial magnets. For example – bar magnet, U shaped magnet, magnetic needle. Permanent magnets are usually made up of how to steel, carbon steel, chromium steel, cobalt steel, tungsten steel, Alnico. Etc. Such materials require a strong magnetic field for the magnetisation. But once they get magnetised they have a residual magnetism for a long period of time
What are the properties of magnetic lines of force
•-•The direction of the magnetic field is taken to be the direction in which the north pole of the compass needle moves inside it . Magnetic field lines originate from the north pole and terminate at the south pole outside of a magnet. The direction of the magnetic field lines inside the magnet is from south pole to North Pole and outside from north to south.
•-• They form continuous closed curves.
-••The magnetic field lines never intersect each other. If they intersect there will be two directions for the magnetic field which is not possible.
•-• The density of magnetic lines decreases as the distance between the poles increases.
•-• Magnetic strength increases at the dense magnetic field lines.The strength of magnetic field is shown by the degree of closeness of the field lines
•-• The tangent on any point of the magnetic field gives the direction if the magnetic field.
How can a magnet attract a piece of iron that is not magnetised?
The magnet causes the piece of iron to become temporary magnetised. It involves inducing opposite Pole. Since opposite poles attract and and magnetised piece of iron is always attracted towards a magnet
If you break a magnet into two pieces can we get isolated polls? Give reasons for this and try to explain this on the basis of magnetic field lines
No, we will not get isolated polls bcoz the magnet is always dipole. The magnetic field lines are closed curve that is they not only the surround the magnet but also pass within on the material of the magnet. THUS, when a magnet is broken into two pieces,The end of the broken piece from the where the magnetic field lines emerge out behaves like north pole. Similarly the end of the broken piece from where the magnetic field lines enters into them behave like South Pole. This is how we get two magnets
What of ferromagnetic materials and how to demagnetise a magnet
The materials like iron, nickel, cobalt when placed in a magnetic field get strongly magnetised in the direction of the field that is the fear inside them is greatly enhanced. Such materials are called ferromagnetic materials.
The magnetism of a magnet can be removed by heating it to very high temperature or putting the magnet in a current carrying solenoid in such a way that magnetisation of the magnet is opposite to the applied magnetic field
What are the uses of magnet
Used in radio N stereo speakers
used in Almira and refrigerator
used on video and audio tape
use on hard disk and floppies of computer
used in different children’s toys
used in magnetic resonance imaging MRI
used to lift heavy iron pieces, electric magnetic separation in metallurgy.
You are provided with two similar bars, one is a magnet and the other is a soft iron. How will you distinguish between them without the use of any other magnet or bar?
A magnet when suspended freely will rest only in north-south direction, but the soft iron bar will rest in any direction.
Explain the following :
(a) When two pins are hung by their heads from the same pole of a magnet, their pointed ends moves apart.
(b) Several soft iron pins can cling, one below the other, from the pole of a magnet.
(c) The north end of a freely suspended magnetic needle gets attracted towards a piece of soft iron placed a little distance away from the needle.
(a) When two pins are hung by their heads from the same pole of a magnet, they acquire same polarity. Because like poles repel each other, their pointed ends move apart.
(b) Several soft iron pins can cling one below the other from the pole of a magnet because the magnet induces magnetism in an iron nail which gets attracted by the magnet and clings to it. This magnetized nail magnetizes the other nail near it by magnetic induction and attracts it. This process continues until force of attraction on first nail is sufficient to balance the total weight of all nails in chain.
(c) When a piece of soft iron is placed a little distance away from the needle, the needle induces magnetism to the piece of soft iron. Thus, soft iron piece starts behaving like a magnet and it attracts the magnetic needle towards it.
what is induced magnetism?and state its laws
the magnetism acquired by magnetic material when it is kept near a magnet is callled induced mamgnetism.when a magnet is brought near a magnetic material, the magnetic pole of the magent induces and oppposite polarity on the near end and simlar polarity at the farther end.
laws-
-induction of poles at ends: during magnetic induction, the opposite poleis induced at near end and like pole is induced at other end
-Induction preceds attraction: when a piece of magnetic material is brought near a magnet , it first becomes a magnet by induction and then it is attracted.
- attraction is the not the sure sign of presence of magnetism but repulsion.
Explain why iron filings which are sprinkled on a sheet of cardboard over a bar magnet take up a definite pattern when cardboard is slightly tapped.
The iron filings take up a definite pattern (curved lines). This happens because each piece of iron filing becomes a magnet to the magnetic induction of the magnet. It thus experiences a force in the direction of magnetic field of the bar magnet at that point and aligns itself along curved lines.
What is a neutral point? How is the position of neutral point located with the use of a compass needle?
Neutral points are the points where the magnetic field of the magnet is equal in magnitude to the earth’s horizontal magnetic field, but it is in opposite direction. Hence they cancel each other and Thus the net magnetic field at the neutral points is zero.
Since the net magnetic field is zero at neutral points, the compass needle remains unaffected (i.e. it comes to rest pointing in any direction) at these points and hence, they can be detected.
State the positions of neutral points when a magnet is placed with its axis in the magnetic meridian and with its north pole (i) pointing towards the geographic north and (ii) pointing towards the geographic south.
i) Neutral points will be in east-west direction.
(ii) Neutral points will be north-south direction.
