# Important Questions for Class 12 Chapter 5 - Magnetism And Matter

Important questions based on NCERT syllabus for Chapter 5 - Magnetism And Matter:

(a) The earth’s magnetic field varies from point to point in space.
(b) The earth’s core is known to contain iron. Yet geologists do not regard this as a source of the earth’s magnetism. Why?

Solution:
(a) Yes it changes with time. The time scale is of order of few hundred years.
(b) As molten iron is not ferromagnetic.

Question-2: A closely wound solenoid of 800 turns and area of cross section2.5 × 10–4 m2 carries a current of 3.0 A. Explain the sense in which the solenoid acts like a bar magnet. What is its associated magnetic moment?

Solution:
Given:
N = 800
A = 2.5x10-4 sq. m
I = 3 A
The solenoid acts like a bar magnet along the axis, determined by flow of current.
The magnetic moment associated
m = NIA = 0.6 J / T.

Question-3: Interstellar space has an extremely weak magnetic field of the order of 10–12 T. Can such a weak field be of any significant consequence? Explain.

Solution:
The interstellar distances are very great, and even the small minute field can affect the passage of charged particles.