Year 12s: what will be the first way you research your future options? >>

Year 12s: what will be the first way you research your future options? >>

Year 12s: what will be the first way you research your future options? >>

electricity power question

http://www.scribd.com/mobile/doc/50654250?width=768

I'm stuck on question 4. The correct answer is B.
P=IV
V=IR

So P=I²R

If the new lamp has twice the resistance, it has to have twice the power. So WHY isn't the correct answer C? I need an explanation so I can understand why B is right and not C.

Thank you

Voltage is constant at 230V.

P=IV. P=VI
V=IR therefore V/R=I so P=V^2/R
Double R, half the power

OP

Original post by pratstercs

Voltage is constant at 230V.

P=IV. P=VI
V=IR therefore V/R=I so P=V^2/R
Double R, half the power

I guess it is better to substitute I=V/R into P=VI.

Thanks a lot.

Original post by krisshP

I guess it is better to substitute I=V/R into P=VI.

Thanks a lot.

It's not necessarily better, you just need to remember that the current will change as the resistance changes

OP

Original post by pratstercs

It's not necessarily better, you just need to remember that the current will change as the resistance changes

Thanks

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