E.M.F. Question

[Guest Terabyte]

Hi,

couple of questions i don't have a single clue how to answer.

 

Four identical cells, each of emf 1.5V and internal resistance 2.0 ohms are connected in parallel by joining like terminals together. A 7.0 ohm resistor is then connected from the positive to the negativ eterminals.

Calculate the current through the 7.0 ohm resisitor!?!?!?

 

 

and...

 

A generator of emf 20v and internal resistance 0.50 ohms is used to charge a car battery of emf 12V and internal resistance 0.10 ohm. They are connected in series together with a resistance R whose value is adjusted to give a charging current of 2.0A.

 

what is:

 

total emf in the circuit

The value of R

the power of the generator

the total rate of dissipation of lectrical energy

the rate at which the battery stores chemical energy

the efficiency of the whole operation..

 

What The Hell!?!?

 

 

Please any help to any of the above would be very much appreciated

[The Rebel]

Hmmmm, takes me back to the days of my HNC eletronics . . .. last year.

 

The 1st question has three choices to solve it, Norton's theorum, Thevein's theorum or Superposition theroum.

 

The 2nd seems easier, as its simply ohms law. The power of the generator is given by its emf * circuit current, the dissipation rate is how much the resistance dissipates, and the chemical rate battery emf * circuit current.

 

Efficiency is the power taken by the load (battery) divided by the power supplied by the source (generator)