# What is the power of this bulb

1. Jan 12, 2013

### hms.tech

1. The problem statement, all variables and given/known data

See attachment
The question asks to calculate the brightness of the bulbs(g and h) in this new configuration.

2. Relevant equations

Since brightness $\propto$ Power

P= $V^{2}$/R
P= $I^{2}$R
E.M.F of One cell : V

3. The attempt at a solution

I used the equation P = V^(2)/R

Since the Voltage across "g" will be 2V and its Resistance is exactly the same as in the reference Attachment, "g" will be brighter than normal.
Similarly, since the Voltage across "h" is going to be V, "h" must be of normal brightness.

I am not sure if my answers make sense since if we apply the 2nd formula : P=R*I^2
we would get a different set of results .

Is it O.K to just rely on one of the two formulas and deduce the final answer based on say P=V^(2)/R ? Would the answers be authentic ?

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2. Jan 12, 2013

### haruspex

Not if you do it correctly. Pls post your working.