NCERT Solutions For Class 10 Science Chapter 12 Electricity

(a)  Due to high melting point and high resistivity of tungsten, it does not burn at a high temperature. As the electric lamps glow at very high temperatures hence, the tungsten is used as heating element of electric bulbs.

(b)  Bread toasters and electric irons are made of alloy because resistivity of an alloy is more than that of pure metals. Due to high resistivity, they produce large amount of heat.

(c)  In a series circuit, there is a voltage distribution. Each element of a series circuit receives a small voltage for a large supply voltage. Thus, the amount of current decreases and the device becomes hot. Therefore, series arrangement is not used in domestic circuits.

(d)  Resistance (R) of a wire is inversely proportional to its area of cross-section (A).

(e)  The wires made of copper or aluminium have low resistivity and they are good conductors of electricity. Therefore, they are frequently used for electricity transmission.

\begin{array}{l}Given,\text{ R = 8 }\Omega \\ \text{ I = 15 A }\\ Rate\text{ of heat produced can be expressed as power,}\\ {\text{ P = I}}^{\text{2}}R\\ On\text{ putting the values,}\\ \text{ P = }{\left(\text{15 A}\right)}^2\times 8=1800\text{ W or }1800\frac{J}{s}.\end{array}

\begin{array}{l}(i)\text{ Given, Potential difference, V = 6 V}\\ {\text{ R}}_{\text{1}}{\text{ = 1 Ω, R}}_{\text{2}}\text{ = 2 Ω}\\ \therefore {\text{ Equivalent resistance in series, R = R}}_{\text{1}}{\text{+ R}}_{\text{2}}\\ =\text{ (1+2) Ω = 3 Ω}\\ \text{ On using the relation,}\\ \text{ V = IR (I = current through the circuit)}\\ \\ \therefore \text{ I = }\frac{\text{V}}{\text{R}}\text{ = }\frac{\text{6}}{\text{3}}\text{ = 2 A}\\ \text{ Now, power in the circuit}\\ {\text{ P = I}}^{\text{2}}{\text{R = (2)}}^{\text{2}}\text{×2=8 W}\text{.}\\ \text{(ii) Given, potential difference, V = 4 V}\\ {\text{ R}}_{\text{1}}=\text{12 }\Omega ,{\text{ R}}_2=2\Omega \\ \text{ The voltage across each component of a }\\ \text{ parallel circuit remains the same}\text{. Hence, voltage across}\\ 2\Omega \text{ resistor will be 4 V}\text{.}\\ \text{ Power consumed by 2 }\Omega \text{ is given by}\\ \text{ P = }\frac{V^2}{R}=\frac{4^2}{2}=\text{ 8 W}\text{.}\end{array}

\begin{array}{l}Given,\text{ Supply voltage, V = 220 V}\\ \text{ Resistance, R = 24 }\Omega \\ \text{(i) When coils are used separately:}\\ \text{ By using the relation,}\\ {\text{ V = I}}_{\text{1}}{\text{R}}_{\text{1}}\\ {\text{ Where, I}}_{\text{1}}\text{ = current flowing through the coil}\\ \therefore {\text{ I}}_{\text{1}}\text{= }\frac{\text{V}}{{\text{R}}_{\text{1}}}\text{ = }\frac{\text{220}}{\text{24}}\text{ = 9}\text{.166 A}\text{.}\\ \\ \text{(ii) When coils are connceted in series:}\\ \text{ total resistance of the two coils}\\ {\text{ R}}_{\text{2}}\text{ = (24+24) }\Omega \text{ = 48 }\Omega \\ \text{ By using the relation,}\\ {\text{ V = I}}_2{\text{R}}_2\\ \therefore {\text{ I}}_{\text{2}}\text{= }\frac{\text{V}}{{\text{R}}_{\text{2}}}\text{ = }\frac{\text{220}}{\text{48}}\text{ = 4}\text{.58 A}\text{.}\\ \text{(iii) When coils are connceted in parallel:}\\ {\text{ Total resistance (R}}_{\text{3}})\text{ would be}\\ \frac{1}{{\text{R}}_{\text{3}}}=\frac{1}{24}+\frac{1}{24}=\frac{2}{24}\\ or,{\text{ R}}_{\text{3}}=12\Omega \\ \text{ On using the relation}\\ {\text{ V = I}}_3{\text{R}}_3\\ \therefore {\text{ I}}_3=\frac{V}{{\text{R}}_3}=\frac{220}{12}=18.33\text{ A}\text{.}\end{array}

(i) 

(ii)

\begin{array}{l}\text{Two resistors of 6 }\Omega \text{ are in series}\text{. Their equivalent}\\ \text{resistance will be = (6+6) }\Omega \text{ = 12 }\Omega \\ \text{The third 6 }\Omega \text{ resistor is connected in parallel with 12 }\Omega .\\ {\text{Hence, equivalent resistance (R}}_{\text{2}})\\ \frac{1}{{\text{R}}_{\text{2}}}=\frac{1}{12}+\frac{1}{6}=\frac{3}{12}=\frac{1}{4}\\ {\text{or, R}}_{\text{2}}\text{ = 4 }\Omega \end{array}

When the graph is plotted between voltage and current then, it is called V-I characteristics. Here, the voltage is plotted on X axis and current is plotted on Y axis.

A voltmeter need to be connected in parallel in a circuit to measure the potential difference between two points.

The correct option is (d).