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ELECTRICITY
- What is the SI Unit of electric Potential?
- What do you mean by the statement; "The electric potential between the points A and B is 1 V"?
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There are two electric bulbs, one marked 60W 220V and the other marked 100W 220V. Which one of the
two has a higher resistance?
- Of the two; a toaster of 1 kW and an electric heater of 2 kW, which has higher resistance?
- Name a metals which offers higher resistance to the passage of electricity than copper.
- Calculate the ratio of resistances of a 50W bulb and a 25 W bulb.
- Why is tungsten preferred to make the filament of an incandescent lamp?
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A wire of resistance 10 Ω is bent in the form of a circle. What is the effective resistance between the two points at the ends of any one of the diameter of the circle?
HOTS
Q.1 What is represented by joule/coulomb?
Q.2 A charge of 2C moves between two plates, maintained at a p.d of 1V. What is the energy acquired by the charge?
Q.3 Why are copper wires used as connecting wires?
Q.4 A wire of resistivity ρ is stretched to double its length. What is its new resistivity?
Q.5 What is the resistance of connecting wire?
Q.6 What is the resistance of an ammeter?
Q.7 What is the resistance of a Voltmeter?
Q.8 Which has more resistance: 100W bulb or 60W bulb?
Q.9 How will you join three resistances, each of 2Ω so that the effective resistance is 3Ω ?
Q.10 What happens to the current in a circuit if its resistance is doubled?
Q.11 What happens to the resistance of a circuit if the current through it is doubled?
Q.12 How does the resistance of a wire depend upon its radius?
Q.13 Two wires are of the same length, same radius, but one of them is of copper and the other is of iron. Which will have more resistance?
Q.14 Two wires of same material and same length have radii r1 and r2. Compare their resistances.
Q.15 Given a resistors each of resistors R. How will you combine them to get the ( i ) maximum and (ii) minimum effective resistance? What is the ratio of the maximum to minimum resistance?
Q.16 A wire of length L and resistance R is stretched so that its length its doubled. How will its (a) Resistance change (b) Resistivity change ?
Q.17 Two students perform the experiments on series and parallel combinations of two given resistors R1 and R2 and plot the following V-I graphs. Which of the graphs is (are) correctly labelled in terms of the words ‘series’ and parallel’ Justify your answer.
Q.18 A household uses the following electric appliances :
(i) Refrigerator of rating 400W for ten hours each day.
(ii) Two electric fans of rating 80W each for twelve hours each day.
(iii) Six electric tubes of rating 18W each for 6 hours each day.
Calculate the electricity bill of the household for the month of June if the cost per unit of electric energy is Rs. 3.00.
Q.19 Ammeter burns out when connected in parallel. Give reasons.
Answers
A.1 It represents potential difference.
A.2 W=QV=2×1=2J
A.3 The electrical resistivity of copper is low.
A.4 It remains same because resistivity depends on nature of material.
A.5 The resistance of a connecting wire, which is made of good conductor, is negligible.
A.6 The resistance of an ammeter is very small and for an ideal ammeter, its value is zero.
A.7 The resistance of a voltmeter is very high and for an ideal voltmeter, its value is infinity.
A.8 As R is inversely proportional to P.Thus, the resistance of 60W bulb is more.
A.9 A parallel combination of two resistances (which will be 1Ω) joined in series with the third resistance (2 Ω)
A.10 As I ∝1/R, the current is reduced to half of its previous value.
A.11 The resistance of the circuit does not depend on the current through it.
A.12 As R ∝ 1/A, R ∝ 1/πr2 i.e. R ∝ 1/r2.
A.13 As R = ρl/A, but A and l are same it depends only on resistivity and it is more for iron so iron has more resistance.
A.14 If R1 and R2 are resistances, then R1/R2 = r2 2/r1 2 because |
