Ques.31. For which of the following materials the net magnetic moment should be zero?
Diamagnetic materials
Ferrimagnetic materials
Antiferromagnetic materials
Antiferrimagnetic materials
Answer.3. Antiferromagnetic materials
Explanation:-
Antiferromagnetic materials are very similar to ferromagnetic materials, in which the atomic magnetic moments are aligned in an antiparallel manner As a consequence, the magnetization is canceled out, and the net magnetic moment should be zero. The Antiferromagnetic material seems to have similar behavior to the paramagnetic material, that is, no net magnetization. Antiferromagnetic materials become paramagnetic above the Néel temperature.
Ques.32. Substances that have permeability less than the permeability of free space are known as
Diamagnetic
Ferromagnetic
Paramagnetic
Bipolar
Answer.1. Diamagnetic
Explanation:-
The magnetic materials can be classified on the basis of magnetic property namely relative permeability μr. In general, a material is said to be non-magnetic if the value of μr is less than 1 or approximately equal to 1. While the material is said to be magnetic if the value of μr is greater than or equal to 1.
Diamagnetic materials are materials with relative permeabilities slightly smaller than 1 (μr < 1). This class includes important materials such as mercury, gold, silver, copper, lead, silicon, and water. The relative permeability of most diamagnetic materials varies between 0.9999 and 0.99999 (susceptibility varies between (-10-5 and -10–4), and for most applications, they may be assumed to be nonmagnetic.
Ques.33. When a low flying aircraft passes overhead, we sometimes notice a slight shaking of the picture on our TV screen. This is due to
Diffraction of the signal received from the antenna
Interference of the direct signal received by the antenna with the weak signal reflected by the passing aircraft
Change of magnetic flux occurring due to the passage of aircraft
Vibration created by the passage of aircraft
Answer.3. Change of magnetic flux occurring due to the passage of current
Explanation
When a low flying aircraft is passing overhead, then it causes a change in magnetic flux and thus causes a disturbance in the picture on our TV.
Ques.34. According to Lenz’s law of electromagnetic induction,
The induced emf is not in the direction opposing the change in magnetic flux
The relative motion between the coil and magnet produces the change in magnetic flux
Only the magnet should be moved towards the coil
Only the coil should be moved towards the magnet
Answer.2. The relative motion between the coil and magnet produces the change in magnetic flux
Explanation:-
According to Lenz’s law of electromagnetic induction, the relative motion between the coil and magnet produces a change in magnetic flux.
Ques.35. Paramagnetic materials have relative permeability
Slightly less than unity
Equal to unity
Slightly more than unity
Equal to that ferromagnetic materials
Answer.3. Slightly more than unity
Explanation
Generally, magnetic materials are classified into three major parts namely diamagnetic, paramagnetic and ferromagnetic. If a value of μr is slightly less than unity then it is a diamagnetic material (μr < 1).
If the value of μr is slightly greater than unity, then it is paramagnetic material (μr ≥ 1). If the value of μr is very large than unity (μr>>1), then it is the ferromagnetic material.
The substances, which when placed in an external magnetizing field, get magnetized feebly in the direction of the magnetizing field are called paramagnetic. Paramagnetism is due to the presence of unpaired electrons in the material, so all atoms with incompletely filled atomic orbitals are paramagnetic. Due to their spin, unpaired electrons have a magnetic dipole moment and act like tiny magnets.
Examples of paramagnetic substances are Aluminium, antimony, platinum, manganese, sodium, chromium, copper chloride, liquid oxygen, titanium etc.
The magnetic susceptibility expresses the responsiveness of a material to the applied magnetic field and can vary with the external applied magnetic field.
The symbol for magnetic susceptibility is χ and magnetic susceptibility is a number with no units.
Materials with positive susceptibility have a field-induced within them that results in a total field that is greater than the strength of the magnetic field in which they are placed. Such materials are described as paramagnetic.
Materials with negative susceptibility have an induced field the opposes the field in which the material has been placed, so the total field within the material is lower than the field in which they are placed. Such materials are described as diamagnetic.
For materials with positive susceptibility, the material is pushed toward stronger magnetic fields as it tends to lower potential energy whereas an opposite response for materials with negative susceptibility. Hence, materials with negative susceptibility (diamagnetic materials) are repelled and pushed toward weaker magnetic fields and materials with positive susceptibility (paramagnetic, ferromagnetic, ferromagnetic, and antiferromagnetic) are pulled toward stronger magnetic fields.
Ques.37. For a given wire-wound core, an increase in current through the coil
Reverses the flux lines
Causes no change in flux density
Decreases the flux density
Answer.1. Increase the flux density
Explanation
Flux density B = φ/N.
φ = Flux.
N = No. on turns.
As current increases, flux increases then obviously flux density increases because the flux is directly proportional to flux density.
Ques.38. What will be the current passing through the ring-shaped air-cored coil when the number of turns is 800 and ampere-turns are 3200?
2
4
6
8
Answer.2. 4
Explanation
Given ampere-turns = 3200
Number of turns = 800
⇒ Current passing through the ring = 3200/800 = 4A
Ques.39. In the left-hand rule, the forefinger always represents
Magnetic field
Current
Voltage
The direction of the force on the conductor
Answer.1. Magnetic field
Explanation
Fleming’s left-hand rule tells us the direction of the force on the wire. Hold the thumb and first two fingers of your left hand so that they are at right angles to each other.
If the first finger points in the direction of the magnetic field the second finger points in the direction of the current, then the thumb points in the direction of the thrust (force).
Ques.40. The Biotsavart’s law is a general modification of
Kirchhoff’s law
Lenz’s law
Ampere’s law
Faraday’s laws
Answer.3. Ampere’s law
Explanation
Biot-Savart’s law describes the three different types of currents, which is nothing but the filament or line current, surface current, and volume current. Hence, this law is a general modification of Ampere’s circuital law.
