Question

A student has two resistors- 2 Ω and 3 Ω. She has to put one of them in place

of R2 as shown in the circuit. The current that she needs in the entire circuit is

exactly 9A. Show by calculation which of the two resistors she should choose.​

Answer 1

Answer:

In this case, for the total resistance to be 3 ohms neither the series or parallel connection can be used but a combination of both is used.

The first two resistors are connected in parallel and the third resistor is connected in series with the first two resistors. Below diagram represents the above mentioned connection type. The resistances connected in parallel have a resistance given as  

2

1

​  

+  

2

1

​  

=  

1

1

​  

=1ohm.

This combined resistance when connected in series with third resistor of 2 ohms gives a total resistance of 2+1 = 3 ohms.

Hence, 2 resistors in parallel connection and 1 resistor in series connection with them gives a total of 3 ohms resistance.