I found P OLD and P NEW.. in forms of resistance. ... how do I relate both of these?

In the old circuit there are two resistors.

 

Are they in series or parallel and what is their combined resistance?

Series .... 2 R

So what is the 'old' power and what is the 'new' power ?

 

You know the voltage and the resistance so what formula do you think is appropriate here?

P = V^2 /R

P old = 36/2R

= 18/R

Pnew = 36/R

Now p new is 2 times old p.... so ans should be C

Did I do this.right?

Yes and NO.

 

Yes you have calculated the total power dissipated in both cases by the 6 volt EMF.

 

But in the first case half this power is dissipated in the internal resistor R and half in the external resistor R.

 

So you lost a factor of 2 in your answer, since you are asked to compare the power in the external resistor only in both cases.

 

Remember always read the question twice.

Edited March 27, 20169 yr by studiot

Oh these are soo bad trick questions

.. Anywayss thanks again