CBSE Class 10 Science 2020 · Paper 31(B) · Question 30(b)

Electricity 5 marks Medium

(a)Define the term Potential Difference and state its SI unit.
(b)Name a device that helps to (i) maintain a potential difference across a resistor, and (ii) change current flowing through a resistor. (c) Calculate the (i) highest, and (ii) lowest resistance that can be obtained by the combination of three resistors of resistances $20 Ω$ , $30 Ω$ and $60 Ω$ .

Answer

Potential difference is work done per unit charge (volt); a cell maintains it, a rheostat changes current; highest resistance $110 Ω$ , lowest $10 Ω$ .

(a) The potential difference between two points in an electric circuit carrying current is the work done to move a unit charge from one point to the other,

V = \frac{W}{Q}

. Its SI unit is the volt (V):

1 V = \frac{1 J}{1 C}

. (b) (i) A cell (or a battery) maintains a potential difference across a resistor; (ii) a rheostat (variable resistance) changes the current flowing through it. (c) (i) Highest: all three in series,

R = 20 + 30 + 60 = 110 Ω

. (ii) Lowest: all three in parallel,

\frac{1}{R} = \frac{1}{20} + \frac{1}{30} + \frac{1}{60} = \frac{6}{60} = \frac{1}{10}

, so

R = 10 Ω

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CBSE Class 10 Science 2020 · Paper 31(B) · Question 30(b)

Answer

From the board paper

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