14
Attempt either (a) or (b) :
(a) (i) What is meant by resistance in an electric circuit ?
(ii) In a series electric circuit comprising a resistor made of a metallic wire, the ammeter reads $500\ \text{mA}$. If the length of wire is doubled and area of cross-section is made half, what will be the new reading of ammeter ?
(iii) How will the resistivity of a wire be affected if both, the length of the wire and its area of cross-section, are doubled ? Justify your answer.
(a) (i) What is meant by resistance in an electric circuit ?
(ii) In a series electric circuit comprising a resistor made of a metallic wire, the ammeter reads $500\ \text{mA}$. If the length of wire is doubled and area of cross-section is made half, what will be the new reading of ammeter ?
(iii) How will the resistivity of a wire be affected if both, the length of the wire and its area of cross-section, are doubled ? Justify your answer.
Show SolutionHide Solution↓
(a) (i) Resistance is opposition to the flow of electrons. /Property of a conductor due to which it retards the motion of electrons in an electric circuit. (1)
(ii) $\text{V=IR}$; $\text{I} = \frac{\text{V}}{\text{R}} = 500\text{mA}$ (½)
$\text{R}=\rho \frac{\text{l}}{\text{A}}$ (½)
$\text{R}_1=\rho \frac{\text{l}_1}{\text{A}_1}$; $\text{l}_1=2\text{l}$; $\text{A}_1=\text{A}/2$
$\text{R}_1=\rho \frac{2\text{l}}{\text{A}/2} = 4\text{R}$ (½)
$\text{I}_1 = \frac{\text{V}}{\text{R}_1} = \frac{\text{V}}{4\text{R}} = \frac{500}{4} = 125 \text{ mA}$ (½)
(iii)
• No change in resistivity. (1)
• It is the property of material only (1)
(ii) $\text{V=IR}$; $\text{I} = \frac{\text{V}}{\text{R}} = 500\text{mA}$ (½)
$\text{R}=\rho \frac{\text{l}}{\text{A}}$ (½)
$\text{R}_1=\rho \frac{\text{l}_1}{\text{A}_1}$; $\text{l}_1=2\text{l}$; $\text{A}_1=\text{A}/2$
$\text{R}_1=\rho \frac{2\text{l}}{\text{A}/2} = 4\text{R}$ (½)
$\text{I}_1 = \frac{\text{V}}{\text{R}_1} = \frac{\text{V}}{4\text{R}} = \frac{500}{4} = 125 \text{ mA}$ (½)
(iii)
• No change in resistivity. (1)
• It is the property of material only (1)