# Important Questions Class 12 Physics Chapter 5

## Important Questions for CBSE Class 12 Physics Chapter 5 – Magnetism and Matter

These Class 12 Physics Chapter 5 Important Questions will teach students about magnetism and matter. After reviewing these CBSE revision notes, students would get an idea of what magnetism and matter are all about. Students would also be better prepared for their exams by studying these Class 12 Physics Chapter 5 Important Questions and could solve several CBSE sample papers after studying these Class 12 Physics Chapter 5 Important Questions.

These notes also come with important formulas and CBSE extra questions that can be used to assess your comprehension.

### Study Important Questions for Class 12 Physics Chapter 5 – Magnetism and Matter

1. How does an increasing applied magnetic field affect a paramagnetic material’s degree of magnetization?

Ans. As the applied magnetic field grows, so does the magnetization’s intensity.

2. A magnetic field-free space is used to cool an iron bar magnet after it has been heated to 1000°C. Will the magnetism remain?

Ans. Iron has a curie temperature of 770°C. Iron loses its magnetic and cannot keep it after being heated to a very high temperature.

3. Can a cyclotron accelerate neutrons? Why?

Ans. The answer is no. A cyclotron cannot accelerate neutrons. This is so because only charged particles may be accelerated by cyclotrons, while neutrons are neutral.

4. What kind of magnetic substance is employed in producing permanent magnets?

Ans. Permanent magnets are made of materials with high coercivity.

5. What physical quantity is represented by the unit Wb/m2? Is the quantity a scalar or a vector one?

Ans. The unit for the magnetic field is W /m2 . It is a vector quantity.

6. Define the angle of inclination caused by the earth’s magnetic field at a specific location.

Ans. The magnetic field of the earth’s surface creates an angle about the magnetic meridian’s horizontal line at a specific location. The angle is called the “angle of inclination”.

7. While soft iron is favoured for producing electromagnets, steel is recommended for producing permanent magnets. Cite one cause.

Ans. (a) Steel has a higher retention rate than soft iron.

(b) Steel has a higher coercivity rating than soft iron.

8. Determine the type of magnetic material and explain how it relates to magnetic susceptibility using the formula relative permeability of a material p = 0.5.

Ans. Paramagnetic. Small and greater than one susceptibility.

9. As the current increases and the coil radius decreases, how does the magnetic field intensity at the core of a circular wire carrying current change?

Ans. As,   B = 04 2Ir

B’ = 04 2 (2I)r2

B’  = 4 (04 2Ir)

B,  = 4B

10. Is a magnetic field generated exclusively by a constant electric current? Explain your response.

Ans. No, an alternating current also creates a magnetic field.

### Important Questions For Class 12 Physics Chapter 5

1. (a) What is meant by “magnetic susceptibility” and how does it relate to “relative magnetic permeability”?

Ans. It describes how easily a substance might become magnetized. It is described as the proportion of the magnetization’s intensity to the magnetic field. The necessary relationship is µr = 1 + χm.

(b). The relative magnetic permeabilities of the two magnetic materials, A and B, are 0.96 and 500, respectively. Which magnetic materials, A and B, are they?

Ans. Paramagnetic and ferromagnetic materials.

2. A magnetic needle that is free to rotate in a vertical position aligns itself with its axis vertically at a specific place on the earth. What are the values of the horizontal component and the angle of dip of the earth’s magnetic field at this location? Where on earth will this location be?

Ans. The earth’s magnetic field has a 90° angle of dip, and its horizontal component is zero. The magnetic pole of the earth is located here.

3. Compared to the other two magnetic materials, “A” has a relative permeability just above unity, whereas “B” has a relative permeability of less than unity. Determine the types of materials “A” and “B.” Will they be susceptible to good or bad things?

Ans. B is diamagnetic, while A is paramagnetic. The susceptibility of “A” will be positive, but the susceptibility of “B” will be negative.

4. On a vertical plane parallel to the magnetic meridian, the northern tip of a magnetic needle with free rotation is 60 degrees below the horizontal. According to reports, the site’s horizontal component of the earth’s magnetic field is 0.4 G. Wherever you are, determine the strength of the earth’s magnetic field.

Ans. Given, = 300

BH = 0.4 G

B = ?

Using the concept, BH = Bcos , we get

B = BHcos = 0.4cos 300 = 0.432 = 0.83 G

5. A magnetic substance has a susceptibility of -0.085. Determine the magnetic material’s kind. This substance is preserved in a non-uniform magnetic field as a specimen. Sketch the altered field pattern.

Ans. Due to its negative susceptibility, the substance is a diamagnetic material. The altered field pattern is depicted as follows.

6. Two specimens, X and Y, are inserted into a uniform magnetic field, which results in the modification depicted below.

(a) Recognize specimens X and Y.

(b) Explain the cause of the field lines’ actions in X and Y.

Ans. (a) X and Y are diamagnetic and paramagnetic, respectively.

(b) This is because a paramagnetic substance has a permeability larger than one, while a diamagnetic substance has less than one.

7. Nickel, antimony, and aluminum are three identical magnetic material specimens stored in a non-uniform magnetic field. In each case, draw the field lines that were modified. Explain your response.

Ans. In response, aluminium is paramagnetic, nickel is ferromagnetic, and antimony is diamagnetic. As a result, they will act in the manner depicted in the accompanying figures.

8. Explain the neutral point and draw lines of force when two similar magnets are spaced apart a certain amount and have their N-poles pointed in the same direction. Track down the neutral points.

Ans. It is close to a magnet where the magnet’s magnetic field perfectly balances the earth’s magnetic field. The figure is presented as follows.

The cross denotes the neutral point.

9. A magnetic substance has a susceptibility of -2.6 x 10-5. Name the kind of magnetic material and list its two characteristics.

Ans. Diamagnetic:

• It has shallow and adverse susceptibility.
• It is less than one for permeability.

10. A homogeneous magnetic field B is parallel to the direction of a bar magnet with magnetic moment M. What is the process involved in rotating the magnet so that its magnetic moment is aligned:

(i) in the opposite field direction?

We know, W = MB (cos 1- cos 2)

Here, 1= 00 and 2 = 1800

W=MB  (cos 00- cos 1800)

W=MB (1 (-1))

W = 2 MB

(ii) in the direction normal to the field?

Here, 1= 00 and 2 = 900

W = MB (cos 00 – cos 900)

W =MB

### Magnetism and Matter CBSE Class 12 Physics Chapter 5 Important Questions

1. Each of the 2.0 X 1024 atomic dipoles in a sample of paramagnetic salt has a dipole moment of 1.5 X 10-23J/T. The sample is chilled to 4.2K while exposed to a homogeneous 0.64T magnetic field. The achieved level of magnetic saturation is 15%. What is the sample’s total dipole moment at a temperature of 2.8K and a magnetic field of 0.98T? Considering Curie’s law.

Ans. Given,

The number of atomic dipoles, n = 2.0 X 1024

Dipole moment of one atomic dipole is M = 1.5 X 10-23J/T

Magnetic Field, B1 = 0.64 T

The sample is then cooled down to a temperature of, T1= 4.2 K

Total dipole moment of atomic dipole, Mtot = n X M

= 2 X 1024 X 1.5 X 10-23

= 30 J/T

Magnetic saturation is achieved at 15%.

Hence, effective dipole moment, M1 = 15100 30 = 4.5 J/T

Now, when the magnetic field is B2 = 0.98 T

Temperature, T2 = 2.8K

Its total dipole moment = M2

Curie’s law states that the ratio of the two magnetic dipoles at various temperatures is as follows:

M2M1 = B2B1 T1T2

M2 = B2T1 M1B1T2

M2= 10.336 J/T

It is evident that the sample’s total dipole moment, at a magnetic field of 0.98T and a temperature of 2.8K, is 10.336J/T.

1. Respond to the following questions.

(a) The earth’s magnetic field changes from location to location in space. Does it alter over time as well? If so, how quickly does it change noticeably?

Ans. The magnetic field of Earth varies over time. It takes a few hundred years for things to alter significantly. It is impossible to ignore how the earth’s magnetic field changes throughout time.

(b) Iron is present in the earth’s core. However, geologists do not regard this as a source of the earth’s magnetism. Why?

Ans. The iron in the Earth’s core is molten. This particular type of iron is not magnetic. As a result, this is not regarded as a source of earth’s magnetism.

(c) The planet’s magnetism is thought to be produced by “i” at the outer conducting regions of the core of the Earth. What could the “battery” (i.e., the energy source) that keeps these currents going be?

Ans. The energy that drives the currents in the outer conducting portions of the earth’s core comes from radioactivity in the planet’s interior. The earth’s magnetism is thought to be caused by these charged currents.

(d) Throughout its 4–5 billion-year history, the earth may have even reversed the direction of its magnetic field multiple times. How can geologists know about the condition of the earth’s field so long ago?

Ans: Throughout Earth’s 4–5 billion-year history, the direction of its field has been reversed multiple times. When rocks solidified, these magnetic fields were weakly recorded in them. The investigation of this rock’s magnetism can provide hints about the geomagnetic past.

(e) The earth’s field significantly changes from its dipole shape (greater than 30,000 km) at considerable distances. What organizations could be to blame for this distortion?

Ans. Earth’s field significantly deviates from its dipole structure at considerable distances (more than 30,000 km) because of the ionosphere. Because of the field of single ions in this area, the earth’s field is altered. These ions generate the magnetic field that surrounds them as they move.

(f) The magnetic field in interstellar space is incredibly feeble, at 10-12 T. Can such a small field have real consequences?

Ans. A very weak magnetic field can bend charged particles travelling in a circle. This might not be apparent for a path with a huge radius. The deflection can impact the flow of charged particles in the vast interstellar vacuum.

1. Respond to the following questions.

(a) A soft iron piece’s hysteresis loop is substantially smaller than a carbon steel piece’s. Which component will release more heat energy if the material is subjected to repeated cycles of magnetization?

Ans. The amount of heat energy dissipated is proportional to the volume of the hysteresis loop. The hysteresis curve area for a piece of carbon steel is considerable. As a result, it dissipates more heat energy.

(b) Is a ferromagnet, for example, a system that exhibits a hysteresis loop, a mechanism for storing memory? Elucidate on this statement’s meaning.

Ans. The magnetization cycle correlates to the magnetization information. Additionally, hysteresis loops can be employed to store this data. The memory or record of a magnetization’s hysteresis loop cycles gives magnetization its value.

(c) What ferromagnetic material is utilized to create “memory stores” in modern computers or coat magnetic tapes in cassette players?

Ans. Ceramics are typically utilized to manufacture memory stores in modern computers and coat magnetic tapes in memory storage devices like cassette players.

(d) Magnetic fields need to be kept out of a specific area of space. Indicate a strategy.

Ans. If soft iron rings encircle a region of space, they can be protected from magnetic fields. These configurations draw the magnetic lines outside of the area.

1. Respond to the following questions about earth’s magnetism.

(a) A vector’s specification requires three values. Give the names of the three independent values typically used to describe the earth’s magnetic field.

Ans. The three independent measurements typically used to describe the earth’s magnetic field are the earth’s magnetic field’s horizontal component, magnetic declination, and angle of dip.

(b) A place in southern India has a dip angle of roughly 18°. In Britain, would you anticipate a bigger or smaller dip angle?

Ans. The distance between a place and the North or South Pole determines the dip angle at that point. Due to Britain’s proximity to the magnetic North Pole on the globe, the dip angle there would be greater (approximately 70°) than in southern India.

(c) Would magnetic field lines in Melbourne, Australia, appear to emerge from the ground or penetrate it if you created a map of them?

Ans. An enormous bar magnet with its north pole close to the geographic South Pole and its south pole close to the geographic North Pole is hypothetically thought to be buried inside the earth. From a magnetic north pole, magnetic field lines extend, and they come to an end at a magnetic south pole. As a result, Melbourne, Australia’s field lines on a map showing the earth’s magnetic field lines would appear to emerge from the ground.

(d) If a compass were to be placed directly on the geomagnetic north or south pole, which way would it point if it were free to travel in the vertical plane?

Ans. The horizontal plane will be open for the compass’s movement. In addition, if a location is on the geomagnetic North Pole or South Pole, respectively, the earth’s field is exactly vertical to the magnetic poles. In this case, the compass can point in any direction.

(e) It is asserted that the earth’s field closely resembles the field because of a dipole with a magnetic moment of 8 X 1022 JT-1 that is situated in the middle of the planet. In some methods, check the size of this number.

Ans. Given,

Magnetic moment, M = 8 x 1022 JT-1

Radius of earth, r= 6.4 X 106 m

Magnetic field strength, B = 800 X 4 X 10-7X 1.2 X 35002 X 0.15 = 4.48 T

Where, 0 = Permeability of free space = 4 X 10-7 TmA.

4 X 10-7X 8 X 10224 X (6.4 X 106)3 = 0.3 G

This amount is on par with the visual field on Earth in terms of magnitude.

(f) According to geologists, several local poles on the planet’s surface are oriented in different directions in addition to the major magnetic N-S poles. How is that conceivable?

Ans. On the surface of the globe, there are, in fact, a number of local poles that are oriented differently. A local N-S pole is an example of a magnetised mineral deposit.

1. Where will the new null points be if the bar magnet in exercise 5.13 is rotated 180° degrees?

Ans. The magnetic field on the magnet’s axis at a distance d1of 14 cm can be expressed as as follows.

B1 = 04 2Md13 = H

Here,

The magnetic moment is M.

The permeability of free space is 0.

H is the horizontal component of the given magnetic field at d1.

The neutral point will be on the equator when the bar magnet is rotated through 180°.

Additionally, the magnetic field of the magnet at a distance d2 along its equatorial line can be expressed as follows.

B2 = 04 Md2 3 = H

Equating, B1 and B2, we obtain

2d13 = 1d2 3

d2 = d1(12)1/3

14 X 0.794 = 11.1 cm

As an outcome, the new null point will be 11.1 cm apart from the traditional bisector.

### Conclusion

To help students with their exam preparation, Extramarks provides Class 12 Physics Chapter 5 Important Questions. Extramarks also provides the best quality CBSE past years’ question papers based on NCERT books and according to the latest CBSE syllabus. The questions are well-structured and cover all the important concepts. These can be of great help in last-minute revisions.

Q1-How does a ferromagnetic substance can be converted into paramagnetic substance?

ANSWhen a paramagnetic substance is heated then its domain starts to break and alignment of magnetic moment of particles get disturb. After sufficient heating, all particles have random direction of magnetic dipole moment. At this stage, substance becomes paramagnetic.

## Please register to view this section

### 1. A magnetic substance has a permeability of 0.9983. Identify the class of magnetic materials that it stands for.

It stands for diamagnetic substances.

### 2. A magnetic substance has a susceptibility of 1.9 10-5. Identify the class of magnetic materials that it stands for.

It stands for a paramagnet material.

### 3. Where on Earth's surface does the angle of dip measure 90 degrees?

On Earth’s surface, the angle of dip is 90 degrees at the magnetic poles.

### 4. Where exactly on Earth's surface is the angle of dip zero?

The angle of dip is 0° at the magnetic equator.

### 5. A material's relative permeability is µr = 400. Determine the type of magnetic substance.

It is ferromagnetic.