Three resistance of magnitudes `20Omega,30Omega and 40Omega` are connected in series.(i) What is the equivalent resistance? (ii) IF the potential difference across the resistance `20Omega` is 1V, calculate the potential differences across the other two resistances and also the total potential difference across the combination.

Explanation

(i) Equivalent resitance,R=20+30+40= `90 Omega`
(ii) For the resistance of `20 Omega`,
current ,I= `(potential dif ference)/(resistance)=1/20A`
Since it is a series combination , the current everywhere is `1/20A.`
`therefore` Potential difference across `30 Omega` resistance
`=1/20 times 30=1.5V`
and across the `40 Omega` resistance `=1/20 times 40-2.0 V`
Potential difference across the combination
`=1/20times90=4.5V`