When R increases, power decreases?

Question:

An electric kettle is rated 230V and 2.5kW.

c) If the element is replaced by one of higher resistance, will the power increase or decrease?

The answer says I have to use P=V^2/R relationship and therefore, as R increases, P decreases. But why do I have to use this equation and not the P = I^2*R one?

Thanks

Reply 1

thebassking

9

Je3y

Question:

An electric kettle is rated 230V and 2.5kW.

c) If the element is replaced by one of higher resistance, will the power increase or decrease?

The answer says I have to use P=V^2/R relationship and therefore, as R increases, P decreases. But why do I have to use this equation and not the P = I^2*R one?

Thanks

because the voltage will stay constant, the current will change according to V = IR

Reply 2

Je3y

OP

4

thebassking

because the voltage will stay constant, the current will change according to V = IR

Why is voltage constant? (probably a stupid question..)

Reply 3

thebassking

9

Je3y

Why is voltage constant? (probably a stupid question..)

I think its something to do with the mains voltage not changing and so it remains constant (thats what i assumed to answer your question!)

Reply 4

teachercol

9

All devices connected to the mains are connected in parallel so they all have the same Pd and the currents will be different.

Devices connected in series would have the same current and the PDs would be different - you'd use I^2 R then.

When R increases, power decreases?

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