Power electricity

[Niha afzal]

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

[studiot]

In the old circuit there are two resistors.

 

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

[Niha afzal]

Series .... 2 R

[studiot]

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?

[Niha afzal]

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?

[studiot]

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, 2016 by studiot

[Niha afzal]

Oh these are soo bad trick questions

.. Anywayss thanks again