CBSE Class 10 Science 2020 · Paper 31/4/1 · Question 29(a)

Electricity 5 marks Medium

Draw a schematic diagram of a circuit consisting of a battery of 3 cells of 2 V each, a combination of three resistors of

10 Ω

20 Ω

and

30 Ω

connected in parallel, a plug key and an ammeter, all connected in series. Use this circuit to find the value of the following :

Answer

Currents are 0.6 A, 0.3 A and 0.2 A; total current 1.1 A; effective resistance $\frac{60}{11} Ω \approx 5.45 Ω$ .

Circuit: the battery of three

2

V cells, the plug key, the ammeter and the parallel combination of the

10 Ω

20 Ω

and

30 Ω

resistors all joined in one series loop, as in the figure. (a) Each resistor has the full

6

V across it, so

I_{1} = \frac{6}{10} = 0.6

I_{2} = \frac{6}{20} = 0.3

A and

I_{3} = \frac{6}{30} = 0.2

A. (b) Total current

I = 0.6 + 0.3 + 0.2 = 1.1

A. (c) Total effective resistance

R_{p} = \frac{V}{I} = \frac{6}{1.1} = \frac{60}{11} Ω \approx 5.45 Ω

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