Hysteresis

Q.

Explain the energy losses in a transformer. How are they minimized?

Q.

What four factors affect the induced emf?

Q.

What is the difference between iron loss and copper loss?

Q.

Out of soft iron and steel which has more coercivity and less retentivity?

Q.

A small bar magnet is moved through a coil at constant speed from one end to the other. Which of the following series of observations will be seen on the galvanometer $G$ attached across the coil?

Three positions shown describe (a) the magnets entry (b) magnet is completely inside (c) magnets exit

1. 

2. 

3. 

4. 

Q. Hysteresis loops for two magnetic materials A and B are given below. These materials are used to make magnets for electric generators, transformer core and electromagnet core. Then it is proper to use

1. A for electric generators and transformers
2. A for electromagnets and B for electric generators
3. A for transformer and B for electric generators
4. B for electromagnets and transformers

Q.

A permanent magnet has properties of retentivity and coercivity respectively as

1. high-high

2. low-low

3. low-high

4. high-low

Q. A bar magnet has coercivity $4\times {10}^{3}A{m}^{-1}$ It is desired to demagnetise it by inserting it inside a solenoid 12 cm long and having 60 turns. The current that should be sent through the solenoid is

1. 2 A
2. 4 A
3. 6 A
4. 8 A

Q. Heat generation in magnetization and demagnetization of a material is maximum when it has

1. High coercitivity and low retentivity
2. High retentivity and low coercivity
3. High coercivity and high retentivity
4. Low coercivity and low retentivity

Q. Magnetic flux density, magnetising field, magnetic permeability, magnetic susceptibility, intensity of magnetisation are VECTOR or SCALAR quantity?

Q. Those magnetic materials are best suited for making armature and transformer cores which have_____permeability and ________ hysterisis loss.

1. high, high
2. low, high
3. high, low
4. low, low

Q.

How does a magnet get demagnetized?

Q. Hard ferromagnetic material is characterized by,

1. Narrow hysteresis loop
2. Broad hysteresis loop
3. Absence of hysteresis
4. Either $\left(A\right)$ or $\left(B\right)$

Q.

How do you plot a hysteresis curve?

Q. Answer the following questions:(a) Explain qualitatively on the basis of domain picture theirreversibility in the magnetisation curve of a ferromagnet. (b) The hysteresis loop of a soft iron piece has a much smaller areathan that of a carbon steel piece. If the material is to go throughrepeated cycles of magnetisation, which piece will dissipate greaterheat energy? (c) ‘A system displaying a hysteresis loop such as a ferromagnet, isa device for storing memory?’ Explain the meaning of thisstatement. (d) What kind of ferromagnetic material is used for coating magnetictapes in a cassette player, or for building ‘memory stores’ in amodern computer? (e) A certain region of space is to be shielded from magnetic fields.Suggest a method.

Q. Out of soft iron and steel which has more coercivity, less retentivity.

1. iron
2. steel
3. both are equal
4. can't say
   

Q. The time period of a freely suspended bar magnet in a field is t.if this magnet of pole strength m is divided into four parts such that the length and width of each part is half that of initial one.then the time period of each part when suspended freely in same magnetic field will be

Q. Magnetic force required to demagnetize the material

1. retainity
2. coercivity
3. hysteresis
4. energy loss

Q. The mass of a specimen of a ferromagnetic material is $0.5\text{kg}$ and its density is $8000{\text{kg/m}}^3$. What is the energy equivalent area of hysteresis loop of alternating magnetizing field of frequency $100\text{Hz}$, if the hysteresis loss per second is $240\times {10}^{-3}\text{J/s}$?

1. $3.84{\text{J/m}}^3$
2. $1.92{\text{J/m}}^3$
3. $38.4{\text{J/m}}^3$
4. $19.2{\text{J/m}}^3$

Q. What is hysteresis? Define the terms 'coercivity' and 'retentivity' of a ferromagnetic material.

Q. The $\chi$ vs $\frac{1}{T}$ graph for an alloy of paramagnetic nature is shown in fig. The curie constant is,

1. $57\text{K}$
2. $50\text{K}$
3. $570\text{K}$
4. $500\text{K}$

Q. A uniform thin constantan wire of ressistance R is bent like acircle. P&Q r two points on the wire such that the arc PQ subtends an angle THETA at the centre. Effective resistance b/w P&Q is

Q. Needles $N_1,N_2$ and $N_3$ are made of a ferromagnetic, a paramagnetic and a diamagnetic substance respectively. A magnet when brought close to them will

1. Attract all three of them
2. Attract $N_1$ and $N_2$ strongly but repel $N_3$
3. Attract $N_1$ strongly, $N_2$ weakly and repel $N_3$ weakly
4. Attract $N_1$ strongly, but repel $N_2$ and $N_3$ weakly

Q. Point out the wrong statement about the magnetic properties of soft iron and steel

1. Retentivity of soft iron is more than retentivity of steel.
2. Coercivity of soft iron is less than coercivity of steel.
3. Area of B-H loop in soft iron is smaller than the area of B-H loop for steel
4. Area of B-H loop in soft iron is greater than the area of B-H loop for steel

Q. A steel wire of original length 1 m and cross-sectional area 4 mmsquare is clamped at the two ends so that it lies horizontally and without tension. If a load of 2. 16 kg is suspended from the middle point of the wire, what would be its vertical depression? Y of the steel = 2*10 power 11 Nm -2 and take g=10 ms-2

Q. State whether True or False :

1. True
2. False

Q. The material for making permanent magnets should have

1. high retentivity, high coercivity
2. low retentivity, high coercivity
3. high retentivity, low coercivity
4. low retentivity, low coercivity

Q. The $\text{B-H}$ curve for a ferromagnet is shown in the figure. The ferromagnet is placed inside a long solenoid with $1000\text{turns/cm}$. The current that should be passed in the solenoid to demagnetize a ferromagnet completely is:

1. ${10}^{-2}\text{A}$
2. ${10}^{-4}\text{A}$
3. ${10}^{-3}\text{A}$
4. ${10}^{-1}\text{A}$

Q. Permanent magnet has properties retentivity and coercivity respectively as:

1. high-high
2. low-high
3. high-low
4. low-low

Q.

Hysteresis loops for two magnetic materials A and B are given below:

1. A for electromagnets and B for electric generators

2. B for electromagnets and transformers

3. A for electric generators and transformers

4. A for transformers and B for electric generators