Question

Q. 10. Free resistors are connected as shown in adjoining
figure.
The effective resistance i.e., equivalent resistance
between the points A and B is: [ISC 2013]
(a) 4Ω
(b) 5Ω
(c)15Ω
(d) 20Ω
​

Answer 1

Answer:

This combination of resistors follows the concept of Wheatstone Bridge.

When the ratio of the resistors (excluding the middle one) are equal i.e. (R1/R2)=(R3/R4)

, then the current through the bridging resistor is zero.

As we can see (2/3) = (8/12)

Hence, the net resistance will be R=4.

Answer 2

Aswer:

a) 4 ohm

Explanation:

The given arrangement is a Wheatstone Bridge arrangement. Thus no current will flow through 6 ohm resistor.

Thus, the remaining circuit has parallel connections in it.

So the upper arm resistance = (3+2) ohm = 5 ohm

The lower arm resistance = (8+12) ohm = 20 ohm

Let R be the resistance of the circuit,

1/R = 1/5+1/20 (resistance for parallel circuit)

1/R = (4+1)/20 = 5/20 = 1/4 ohm

R= 4 ohm

Ans ) a) 4 ohm