Iron has relative permeability of 100 and conductivity of 1 × 10
A. Aluminium shield about 5 times better than Iron
B. Iron shields about 5 times better than Aluminium
C. Aluminium shield about 10 times better than Iron
D. Iron shield about 10 times better than Iron
Please scroll down to see the correct answer and solution guide.
Right Answer is: B
SOLUTION
Concept:
The shielding capacity of a material is determined by its attenuation constant
\({\rm{α }} = \sqrt {{\rm{\pi f\mu\sigma }}} \)
Calculation
\({{\rm{α }}_{{\rm{Al}}}} = \sqrt {{\rm{\pi f}}{{\rm{\mu }}_{{\rm{Al}}}}{{\rm{\sigma }}_{{\rm{Al}}}}} = \sqrt{\pi \times f \times 1 \times 4 \times 10^7}\)
\({{\rm{α }}_{{\rm{Fe}}}} = \sqrt {{\rm{\pi f}}{{\rm{\mu }}_{{\rm{Fe}}}}{{\rm{\sigma }}_{{\rm{Fe}}}}} = \sqrt{\pi\times f \times 100 \times 10^7}\)
\(\frac{α_{Fe}}{10} = \frac{α_{Al}}{2}\)
αFe = 5 αAl
Iron shield 5 times better than Aluminium.