U r given several identical resistances each of value 10ohms & each capable of carryin a max current of 1 A.It is requied to make a suitable combination of these resistances to produce a resistance of 5 ohm which cancarry current of 4 A.Themin no of resistances required is

4

10

8

20

ans is 8

A carbon & an aluminium wire are connected in series .If the combination has resistance of 30 ohms at 0⁰C,what is the resistance of each wire at 0⁰C so that resistance of the combination does not change with temperature. 

_c=-0.5x10^-3/⁰C _Al=4 x10^-3/⁰C

10 80

80/3 10/3

40/3 80/3

40 80

ans is 80/3 10/3

ans to 1st question)

we need a network to carry 4A and equi resritance of 5ohm

therefore we cant TAKE ALONE series resistors thus parrallel arrange ment is taken with 4 branches now

since 1A flows through each branch the resistors ineach branch need to be equal therefore (x/4)=5 thus x=20

but we have 10ohm only so each branch has 2 such and thus eight

seeking the second answer

Do rate if u understand

PL SOMEONE ANSWER THE 2 Q

we know that R_t=R₀[1+dt].So,the resistance of the combination at t⁰C is

R'=R_c[1+_ct]+R_a[1+_at]=R_c+R_a since the resistance shud not vary with temparature.By substituting the values,we get R_c=8R_a and we already know that their sum is 30.This gives the ans. as 80/3,10/3