Magnetism Question 43
Question: 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
Options:
A) 2 A
B) 4 A
C) 6 A
D) 8 A
Show Answer
Answer:
Correct Answer: D
Solution:
The bar magnet coercivity $ 4\times 10^{3}A{{m}^{-1}} $ i.e., it requires a magnetic intensity $ H=4\times 10^{3}A{{m}^{-1}} $ to get demagnetised. Let i be the current carried by solenoid having n number of turns per metre length, then by definition H = ni. Here $ H=4\times 10^{3} $ Amp turn metre-1 $ n=\frac{N}{l}=\frac{60}{0.12}=500 $ turn metre?1
$ \Rightarrow i=\frac{H}{n}=\frac{4\times 10^{3}}{500}=8.0\ A $
BETA
