ELECTRICITY – 5 Mark Questions

Q1.         (i)  Distinguish between the terms electrical resistance and resistivity of conductor.

(ii)   A    copper wire of resistivity 1.63 × 10-8 Ω-m has cross-section area of 10.3× 10-4 cm2. Calculate the, length of the wire required to make a 20Ω coil.

Q2. Two resistances when connected in parallel give resultant value of 2Ω, when connected in series the value becomes 9 Ω. Calculate the value of each resistance.

Q3.         (i)  Find the value of current I in the circuit given as below:

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           (ii)  You have four resistors of 8 Ω each. Show how would you connect these resistors to have effective resistance of 8 Ω?

Q4.  Three incandescent bulbs of 100 W each are connected in series in an electric circuit. In another set of three bulbs of the same wattage are, connected in parallel to the source.     

(i)  Will the bulb in the two circuits glow with the -same brightness? Justify your answer.

(ii)   Now, let one bulb in both the circuits get fused. Will the rest of the bulbs continue to glow in each circuit?

Give reason.

Q5. A household uses the following electric appliances;

(i)  Refrigerator of rating 400 W for 10 h each day.

(ii)   Two electric fans of rating 80 W each for 6 h daily.           .              .

(iii)   Six electric tubes of rating 18 W each for 6 h daily.

Calculate the electricity bill, for the household   for month   of June, if cost   of electrical energy is Rs.3 per unit

Q6. How will you conclude that the same potential difference (voltage) exists across three resistors connected in a parallel arrangement to a battery?

Q7.  With the help of a circuit diagram prove that when a number of resistors are connected in parallel, the reciprocal of equivalent resistance of the combination is equal to the sum of the reciprocals of the individual resistances of the resistors.

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Find the resistance between  A  and   B  in the following network.

Q8. (a) Two identical resistors each of resistance 10 ohm are connected in:

(i) Series, (ii) Parallel

in turn to a battery of 6V. Calculate the ratio of Power consumed by the combination of resistors In the two cases.

        (b) List two factors on which the resistance of a conductor depends.

       (c) Write a   difference between an ammeter and voltmeter.

Q9. (a)  Two students perform experiments on given resistors R1 and R2 and plot the following V-I graphs. If R1 > R2, which of the two diagrams correctly represent the situation on the plotted curves? Justify your answer.

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        (b) An electric lamp of 24 Ω and a conductor of 6 Ω are connected in parallel to a 12 V battery. Calculate:

(i)  Total resistance,

(ii)  Total current in the circuit,

(iii) Potential difference across the conductor.

Q10. Draw a circuit diagram for a circuit consisting of a battery of five cells of 2 volts each, a 5 Ω resistor, a 10 Ω resistor and  a 15 Ω resistor,  an ammeter and a plug  key; all connected in series. Also connect a voltmeter to record the potential difference across the 15 resistor and calculate:

(i) The electric current passing through the above circuit and

(ii) Potential difference across 50 resistors when the key is closed.

Q11. What is meant by electric current? Name and define S.I. unit in a conductor electron are flowing from B to A. What is the direction of conventional current? Give justification for your answer.

A steady current of 1 Ampere flows through a conductor. Calculate the number of electrons that flow through any section of conductor in 1 second. (Charge on electron = 1.6 × 10-19 C)

Q12. (i) A wire of resistivity p is stretched to double its length which is its new resistivity. Give reason for your answer.

           (ii) Draw a schematic diagram of a circuit consisting of a battery of three cells of 2V each, a 50 Ω resistor, 80 Ω resistor and 120 Ω resistor and a plug key all connected in series.

           (iii) Two wires, one of copper and other of manganese have equal lengths and equal resistances. Which is thicker? (Given that resistivity of manganese is lower than that of copper.)

Q13. (i)  What is meant by the statement that the resistance of a wire is 1 Q?

           (ii) Two identical resistors each of resistance 12 Q are connected

(a) in series 

(b) in parallel, in tum to a battery of 6 V.

Calculate the ratio of power consumed in the combination of resistors in the two cases.

           (iii)   What combination is used for connecting the circuit to measure the potential difference across two points?

Q14. Two conductors A and B of resistances 5Ω and 10 Ω respectively are first joined in parallel and then in series. In each case the voltage applied is 20 V.

(i) Draw the circuit diagram to show the combination of these conductors in each case.

(ii) In which combination will the voltage across the conductors A and 8 be the same?

(iii) In which arrangement will the current through A and B be the same?

(iv) Calculate the equivalent resistance for each arrangement.

Q15. (i) The potential difference between two points in an electric circuit is 1V. What does it mean? Name a device that helps to measure the potential difference across a conductor.

           (ii) Why does the connecting cord of an electric heater does not glow while the heating element does?

           (iii) Electrical resistivities. of some substances at 20°C  are as given below:

Silver                    1. 60 ×10-8 Q-m

Copper                1.62 ×10-8 Q-m

Tungsten              5.2 × 10-8 Q-m

Iron                       10.0 ×10-8 Q-m

Mercury               94.0 ×10-8 Q-m

Nichrome              100 ×10-8 Q-m

Answer the following questions using following data.

(a) Among silver and copper, which one is a better conductor and why?

(b) Which material would you advise to be used in electrical heating devices and why?

Q16. Three incandescent bulbs of 100 W each are connected in series in an electric circuit. In another set, three bulbs of the same voltage are connected in parallel to the same source.

(i) Will the bulbs in the two circuits glow with the same brightness? Justify your answer.

(ii) Now let one bulb in both the circuits get fused. Will the rest of the bulbs continue to glow in each circuit? Give reasons.

Q17.   A wire is cut into three equal parts and then connected in parallel with the same source. How will its

(i)  resistance and resistivity gets affected?

(ii)  How would the total current and the current through the parts change?

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