# Homework Help: Batteries and Internal resistance

1. Oct 7, 2011

### sabak22

A 6.0 V battery has an internal resistance r. The measured voltage (emf of the battery) is 6.0 V. When connected to a resistor R the terminal voltage is 5.9 V and the current is 0.18 A.
I managed to get a) What is the internal resistance r of the battery?
0.556 ohm

as well as b) What is the value of the external resistor R?
32.78 ohm

but i cant figure out what to do when they ask me
c) What is the energy dissipated inside the battery in 4.4 minutes?

and d)When a second identical battery is added in series and the external resistor is R = 29 Ohms what is the resulting current?

2. Oct 7, 2011

### issacnewton

c) Power dissipated inside the battery would be

$$I^2r$$

where r is the internal resistance. once you get power, find the energy consumed inside the battery.......

for part d) , set up Kirchhoff's equation again........

3. Oct 7, 2011

### sabak22

Thank you very much isaacnewton. But I am not quite sure how to solve the d part. Could you please expand a little bit? I am having trouble setting up the second identical battery in the circut.

4. Oct 8, 2011

### issacnewton

have you learned how to use Kirchhoff's rule ?

5. Oct 8, 2011

### sabak22

umm all we've learned this week was that Iin=Iout. Is that supposed to help me? I dont know what to with it.

6. Oct 8, 2011

7. Oct 8, 2011

8. Oct 8, 2011

9. Oct 8, 2011

### issacnewton

you should get some understanding of the voltage law to solve the problem

10. Oct 8, 2011

### sabak22

just a quick question. will the two internal resistances be the same now that another identical battery has beenhadded? If yes then will the r= 0.556 like it was in the first case?

11. Oct 8, 2011

### issacnewton

yes, the internal resistance is the same... its the property of the battery....
but now you have two similar batteries in series......

Edit: which book your teacher is following ?

12. Oct 8, 2011

### sabak22

so what im getting is something like this :

6-0.556-32.78i1-6-0,556-29i2 = 0

Does this make any sense? if not can you please boost me with a little help.

13. Oct 8, 2011

### issacnewton

see, the batteries and the external resistor are in SERIES, so there is only one current throughout.

14. Oct 8, 2011