CBSE Class 10 Science 2019 · Paper 31/2/1 · Question 20(a)

(a) Experiment: (i) Join three resistors of different values in series. (ii) Connect them to a battery, an ammeter and a plug key, all in series. (iii) Plug the key and note the ammeter reading. (iv) Change the position of the ammeter to other places in the circuit - between the resistors and after the last one - and note the reading each time. (v) The ammeter reading is the same in every position. Hence the same current flows through every part of a circuit containing resistors in series. (b) Total resistance $R=5\Omega +10\Omega +15\Omega =30\Omega$. Current $I=\frac{V}{R}=\frac{30\text{V}}{30\Omega }=1$ A. Potential difference across the $15\Omega$ resistor $=IR=1\text{A}\times 15\Omega =15$ V.