Question

an electric iron is rated 220 V - 1 kw under normal working condition find resistance of iron. calculate
1) resistance of iron
2) amount of heat that will be produced in 5 minutes​

Answer 1

Answer:-

• Power=1kw=1000w=P
• Voltage=V=220V
• Resistance=R=?

We know that

$\boxed{\sf p=\dfrac{V^2}{R}}$

$\\ \sf\longmapsto R=\dfrac{V^2}{P}$

$\\ \sf\longmapsto R=\dfrac{(220)^2}{1000}$

$\\ \sf\longmapsto R=\dfrac{48400}{1000}$

$\\ \sf\longmapsto R=48.4\Omega$

$\therefore$Resistance=48.4ohm[/tex]

• Current=I

According to ohms law

$\boxed{\sf \dfrac{V}{I}=R}$

$\\ \sf\longmapsto I=\dfrac{V}{R}$

$\\ \sf\longmapsto I=\dfrac{220}{48.4}$

$\\ \sf\longmapsto I=4.5A$

• Time=5min=300s
• Heat=H

According to Joules law

$\boxed{\sf H=I^2Rt}$

$\\ \sf\longmapsto H=(4.5)^2\times 48.4\times 300$

$\\ \sf\longmapsto H=20.25\times 48.4\times 300$

$\\ \sf\longmapsto H=294030J$

$\\ \sf\longmapsto H=2.9\times 10^5J$

$\\ \sf\longmapsto H=2.9\times 10^2KJ$