CBSE Class 12-science Answered

Dear Student

Say the required temperature=T

at that temperature 

I=0.185 A;  V=30 Volt ==> 

R1=20 ohm
R2=30/0.185 =162.16 ohm

resistance R=s  L/A     s=resistivity,  L =length of the wire, A=crosssectional area.

Because of temperatre raise from 20C to T
there will be increase in area and lingth as well
Expansion in area can be neglected
R2/R1=L2/L1=( L+alphaXT)/L=alphaXT/L
T=   LR2/ (R1 Alpha)= 162.16/(20X4.5X10^-3)=1801.8K

Assuptions are    1)L1=one unit  2) areal expansion is less

Regards
Team
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