Q9 of 11 Page 44

Solve the following problems.

When two resistors are connected in series, their effective resistance is 80 W. When they are connected in parallel, their effective resistance is 20 W. What are the values of the two resistances?

Given:

Effective resistance when two resistors are connected in series =


80Ω


Let us consider the resistances as R1 and R2


R1 + R2 = 80Ω ---(1)


Effective resistance when two resistors are connected in parallel = 20Ω


Effective resistance in case of parallel connection


Therefore = 20Ω ---(2)


Solving eq(1) and eq(2)




R1R2 = 1600


(R1-R2)2 = (R1 + R2)2 - 4R1R2


= 802 - (4×1600)


= 0


R1-R2 = 0 ---(3)


Solving (1) and (3)


we get R1 = R2 = 40Ω


More from this chapter

All 11 →
7

Resistances and are connected as shown in the figure. S1 and S2 are two keys. Discuss the current flowing in the circuit in the following cases.


A. Both and are closed.


B. Both and are open.


C. is closed but is open

 8

Three resistances x1, x2 and x3 are connected in a circuit in different ways. X is the effective resistance. The properties observed for these different ways of connecting x1, x2 and x3 are given below. Write the way in which they are connected in each case. (I-current, V-potential difference, x-effective resistance)

A. Current I-flows through and


B. x is larger than and


C. x is smaller than and


D. The potential across and is the same


E.


F.

9

Solve the following problems.

The resistance of a 1m long nichrome wire is 6 W. If we reduce the length of the wire to 70 cm. what will its resistance be?

 9

Solve the following problems.

If a charge of 420 C flows through a conducting wire in 5 minutes what is the value of the current?