Case Study Questions for Class 12 Physics Chapter 5 Magnetism and Matter
Case Study Question 1:
Read the following case/passage and answer the following questions:
Elements of the Earth’s Magnetic Field. The earth’s magnetic field at a point on its surface is usually characterized by three quantities: (a) declination (b) inclination or dip and (c) horizontal component of the field. These are known as the elements of the earth’s magnetic field. At a place, angle between geographic meridian and magnetic meridian is defined as magnetic declination, whereas angle made by the earth’s magnetic field with the horizontal in magnetic meridian is known as magnetic dip.
(i) In a certain place, the horizontal component of magnetic field is 1/ 3 times the vertical
component. The angle of dip at this place is
(a) Zero
(b) π/3
(c) π/2
(d) π/6
Answer
Answer: (b)(ii) The angle between the true geographic north and the north shown by a compass needle is
called as
(a) inclination
(b) magnetic declination
(c) angle of meridian
(d) magnetic pole
Answer
Answer: (b) magnetic declinationThe angle between the true geographic north and the north shown by a compass needle is called as magnetic declination or simply declination.
(iii) The angle of dip at the poles and the equator respectively are
(a) 30º, 60º
(b) 0º, 90º
(c) 45º, 90º
(d) 90º, 0º
Answer
Answer: (d)(iv) A compass needle which is allowed to move in a horizontal plane is taken to a geomagnetic pole.
(a) It will become rigid showing no movement.
(b) It will stay in any position.
(c) It will stay in north-south direction only.
(d) It will stay in east-west direction only.
Answer
Answer: (a) It will become rigid showing no movementA compass needle which is allowed to move in a horizontal plane is taken to a geomagnetic pole. It will stay in any position as the horizontal component of earth magnetic field becomes zero at the geomagnetic pole.
(v) Select the correct statement from the following:
(a) The magnetic dip is zero at the centre of the earth.
(b) Magnetic dip decreases as we move away from the equator towards the magnetic pole.
(c) Magnetic dip increases as we move away from the equator towards the magnetic pole.
(d) Magnetic dip does not vary from place to place
Answer
Answer: (c) Magnetic dip increases as we move away from the equator towards the magnetic pole.Case Study Question 2:
Earth’s Magnetic Field: The magnetic field of the earth resemble that of a hypothetical magnetic dipole located at the centre of the earth. The axis of the dipole is presently tilted by approximately 11.3º with respect to the axis of rotation of the earth.
The pole near the geographic North pole of the earth is called North magnetic pole and the pole near the geographic South pole is called South magnetic pole.
(i) The strength of the earth’s magnetic field varies from place on the earth’s surface, its value being of the order of
(a) 105 T
(b) 10-6 T
(c) 10-5 T
(d) 108 T
Answer
Answer: (c)(ii) A bar magnet is placed North-South with its North-pole due North. The points of zero magnetic field will be in which direction from centre of magnet?
(a) North-South
(b) East-West
(c) North- East and South-West
(d) None of these
Answer
Answer: (b)(iii) The value of angle of dip is zero at the magnetic equator because on it
(a) V and H are equal
(b) the values of V and H zero
(c) the value of V is zero
(d) the value of H is zero
Answer
Answer: (c)(iv) The angle of dip at a certain place, where the horizontal and vertical components of the earth’s magnetic field are equal, is
(a) 30º (b) 90º
(c) 60º (d) 45º
Answer
Answer: (d)(v) At a place, angle of dip is 30º. If horizontal component of earth’s magnetic field is H, then the total intensity of magnetic field will be
(a) H/2
(b) 2H/√3
(c) H√3/√2
(d) 2H