The circuit at right consists of a bulb in series with an el

The circuit at right consists of a bulb in series with an electrical \"black box\" The following are possible contents for the \"black box.\" All the bulbs are identical. Box C consists of a single piece of connecting wire. Suppose that each of the five boxes is placed, in turn, into the circuit. (Only one box is in the circuit at a time.) Draw the appropriate five circuit diagrams below (show the contents of the boxes in place of the box itself). Use the model that we have developed to rank the five circuits according to the brightness of the indicator bulb in those circuits. Rank the boxes according to their equivalent resistance. Explain. (Do not calculate the resistance of each network; use the model instead.)

Solution

a) put the element of given as it is as they are shown in the place of black box and complete
the circuit.

b) as resistance of circuit increases bulb will get dimmer.

A: resistance of block box is less than R .

two R are connected in parallel.

1/Req = 1/R + 1/R

Req = R/2

B: resistance is equal to R

C: zero resistance.

D: they are in series.

Req = R + R = 2R

E: 1/Req = 1/(R+R) + 1/R

1/Req = 1/2R + 1/R

Req = 2R/3

brightness order:

D < B < E < A < C

c) C < A < E < B < D