Magnetism and Matter Important Questions for CBSE Class 12 Physics Earth’s Magnetic Field and Magnetic Material
Previous Years’ Examination Questions
1 Mark Questions
Ans. The nature of magnetic material is diamagnetic.
2.What are permanent magnets? Give one example. [Delhi 2013]
Ans.Permanent magnets are those magnets which have high retentivity and coercivity The magnetisation of permanent magnet is not easily destroyed even if it is handled roughly or exposed in stray reverse magnetic field, e.g. steel.
3.Where on the surface of the earth’s vertical component of earth’s magnetic field zero? [Delhi 2013C, All india 2011]
Ans. At equator, vertical component will be zero.
4.The horizontal component of the earth’s magnetic field at a place is B and angle of dip is 60°. What is the value of vertical component of the earth’s magnetic field at equator? [Delhi 2012]
5.What is the angle of dip at a place where the horizontal and vertical components of the earth’s magnetic field are equal? [Foreign 2012]
6.A magnetic needle free to rotate m a vertical plane orients itself vertically at a certain place on the earth What are the values of
- horizontal component df the earth’s magnetic field and
- angle of dip at this place? [Foreign 2012]
Ans. (i) The coil is free to move in vertical plane, it means that there is no componerr A the earth’s magnetic field in horizontal direction, so the horizontal component of the earth’s magnetic field is 0.
(ii) The angle of dip is 90°.
7.Where on the surface of earth is the angle of dip 90°? [All India 2011]
Ans. At poles, the angle of dip is 90°.
8.The permeability of a magnetic material is 0.9983. Name the type of magnetic material, it represents. [Delhi 2011]
9.The susceptibility of a magnetic material is 1.9 x 10-5. Name the of magnetic material, it represents. [Delhi 2011]
Ans. The small and positive susceptibility of 1.9 x 10-5 represents paramagnetic substance.
Ans. Negative susceptibility diamagnetic substance.
12. What is the Characteristic property of a diamagnetic material? [Foreign 2010]
Ans. Diamagnetic material acquires magnetisation in the opposite direction of the magnetic field when they are placed in an external magnetic field
13. Define the term magnetic declination. [All India 2009c]
Ans. Magnetic declination The angle between geographical meridian and magnetic meridian at any place of the earth is known as magnetic declination (a) at that place of the earth.
2 Marks Questions
14.Show diagrammatrically the behaviour of magnetic field lines in the presence of
- paramagnetic and
- diamagnetic substances. How does one explain this distinguishing feature? [All ihdia 2014]
Ans. Magnetic permeability of paramagnetic is more than air, so it allows more lines to pass through it while permeability of diamagnetic is less than air, so it does not allow lines to pass through it.
For figure, refer ans. 34.
This difference can be explained as diamagnetic substances repel or expel the magnetic field lines while paramagnetic substance attract the magnetic field lines
15.Out of the two magnetic materials, A has relative permeability slightly greater than unity while B has less than unity. Identify the nature of the materials A and B. Will their susceptibilities be positive r negative? [Delhi 2014]
16. Give two points to distinguish between a paramagnetic and diamagnetic substance.
17. (i) How is an electromagnet different from a permanent magnet?
(ii) Write two properties of a material which makes it suitable for making electromagnet. [All India 2014C]
Ans. An electromagnet consists of a core made of a ferromagnetic material placed inside a solenoid. It behaves like a strong magnet when current flows through the solenoid and effectively loses its magnetism when the current is switched off.
(i) A permanent magnet is also made up of a ferromagnetic material but it retains its magnetism at room temperature for a long time after being magnetised one.
(ii) Properties of material are as below:
- High permeability
- Low retentivity
- Low coercivity
18. The relative magnetic permeability of a magnetic material is 800. Identify the nature of magnetic material and state its two properties. [Delhi 2012]
Ans. Ferromagnetic substance as these substances have very high magnetic permeability.
Properties (i) High retentivity
(ii) High susceptibility
19.(i) How does a diamagnetic material behave when it is cooled to very low temperature?
(ii) Why does a paramagnetic sample display greater magnetisation when cooled? Explain. [Delhi 2012]
Ans. (i) As, the resistance (electrical of metal decreases with decrease in temperature.
But for diamagnetic substances, the variation of susceptibility is very small, i.e. diamagnetic materials are unaffected by the change in temperature (except bismuth). (1)
(ii) Paramagnetic materials when cooled due to thermal agitation tendency alignment of magnetic dipoles decreases. Hence, they shows greater magnetisation.
20.A magnetic needle free to rotate in a vertical plane parallel to the magnetic meridian has its North tip down at 60° with the horizontal. The horizontal component of the earth’s magnetic field at the place is known to be 0.4 G. Determine the magnitude of the earth’s magnetic field at the place. [Delhi 2011]
21.Distinguish between diamagnetic and ferromagnetic materials in terms of
- susceptibility and
- their behaviour in a non-uniform magnetic field. [All India 2011]
22.(i) Write two characteristics of a material used for making permanent magnets?
(ii) Why is core of an electromagnet made of ferromagnetic materials? [Delhi 2010]
23.The horizontal component of the earth’s magnetic field at a place is V3 times its vertical component there. Find the value of the angle of dip at that place. What is the ratio of the horizontal component to the total magnetic field of the earth at that place? [All India 2010c]
24.The horizontal component of the earth’s magnetic field at a place equals to its vertical component there. Find the value of the angle of dip at that place. What is the ratio of the horizontal component to the total magnetic field of the earth at that place? [HOTS, All India 2010C]
31.Define magnetic susceptibility Of a material. Name two elements, one having positive susceptibility and the other having negative susceptibility. What does negative susceptibility signify? [Delhi 2008]
32.Draw a plot showing the variation of intensity of magnetisation with the applied magnetic field intensity for bismuth. Under what condition cfbes a diamagnetic material exhibit perfect conductivity and perfect diamagnetism? [Foreign 2008]
3 Marks Questions
33.A wheel with 8 metallic spokes each 50 cm long is rotated with a speed of 120 rev/min in a plane normal to the horizontal component of the each’s magnetic field. The earth’s magnetic field at the place is 0.4 G and the angle of dip is 60°. Calcu] ate the emf induced between the 3txle and the rim of wheel. How will the value of emf be affected if the number of spokes were increased? [All India 2013]
35.(i) What happens when a diamagnetic substance is placed in a varying magnetic field?
(ii) Name the properties of a magnetic material that makes it suitable for making (a a permanent magnet and (b) a core of an electromagnet. [Foreign 2009]
36.(i) How does angle of dip change as line goes from magnetic pole to magnetic equator of the earth?
(ii) A uniform magnetic field gets modified as shown in the figure below, when two specimens X and Y are placed in it. Identify whether specimens X and Y are diamagnetic, paramagnetic or ferromagnetic. [Foreign 2009]
37.When two materials are placed in an external magnetic field, the behaviour of magnetic field lines is as shown in the figure. Identify the magnetic nature of each of these two materials. [Delhi 2009c]
38.Name the three elements required to specify the earth’s magnetic field at a given place. Draw a labelled diagram to define these elements. Explain briefly how these elements are determining to find out the magnetic field at a given place on the surface of the earth. [Delhi 2008]
- Write the range of relative magnetic permeability of the materials .
- Draw the pattern of magnetic field lines when the materials are placed in external magnetic field. [Delhi 2008]
40.Name and define the elements of the earth’s magnetic field other than the horizontal component of the earth’s magnetic field. Why do we say that at the place like Delhi and Mumbai, a magnetic needle shows the true North direction quite accurately as compared to other places in India? [All India 20011c]
5 Marks Questions
41. (i) A small compass needle of magnetic moment M is free to turn about an axis perpendicular to the direction of uniform magnetic field B. The moment of inertia of the needle about the axis is I. The needle is slightly disturbed from its stable position and then released. Prove that it executes simple harmonic motion. Hence, deduce , the expression for its time period, (ii) A compass needle free to turn in a vertical plane orients itself with its axis vertical at a certain place on the earth. Find out the values of (a) horizontal component of the earth’s magnetic field and (b) angle of dip at the place. [Delhi 2013]
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