Question

Find the emf and internal resistance of a single battery which is equivalent to a combination of three batteries as shown in figure.

Answer 1

The given combination consists of two batteries in parallel and resultant of these two in series with the third one. For parallel combination we can apply, 

Now this is in series with the third one, i.e.,

The equivalent emf of these two is(6 – 3) V or 3 V and the internal resistance will be, (1 + 1) or 2 Ω.

Comments

how do we know whether negative terminal or positive terminal of 3 V will connect with negative of 6V?

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With the type of 3V battery we are using, each side has a different polarity, or positive and negative conductor that determine that direction that the current flows.