TUTORIAL-1 Date:12-08-13

- Discussed in full class

- Discussed with A3,A4

- Yet to be discussed

1. Calculate the resistance of a 100m length of wire having a uniform cross-sectional area of

0.1mm2 if the wire is made of material having a resistivity/specific resistance of 80×10 -8

Ω-m.(800 Ω)

2. Calculate the resistance of a 100 m length of a wire having a uniform area of 0.1 mm2 if

the wire is made of manganin having a resistivity of 50µΩ-cm.(500 Ω)

3. If the wire is drawn out to three times its original length , by how many times would you

expect its resistance to be increased ?(9 times)

4. A platinum coil has a resistance of 3.146 Ω at 40°C and 3.767 Ω at 100°C. Find the

resistance at 0°C and the temperature-coefficient of resistance at 40°C. (Ans. R0=2.732Ω,

α40=1/304 per °C )

5. Find the resistance of a 2000 km cable at 20oC, having a diameter of 0.7 cm. assume

specific resistance of copper at 20oC as 1

58 for 1 m length and 1mm2 cross-section.

(Ans:896.01 Ω)

6. A loading of 5 kW in a heating unit is to be maintained. At an initial temperature of

15°C, a voltage of 200 V is necessary for this purpose. When the unit settles at a steady

temperature, a voltage of 220 V is required to maintain the same loading. Estimate the

final temperature of the heating element, if the resistance temperature coefficient of the

heating element is 0.0006 per °C at 0°C.(368.31°C)

7. Two wires of aluminium and copper have the same resistance and same length. Which of

these two is lighter? Density of copper is 8.9*103 kg/m3 and that of aluminium is 2.7*103

kg/m3. The resistivity of copper of 1.72*10-8 Ω-m and that aluminium is 2.6*10-8 Ω-m.

(Ans: ma/mc = 0.46 aluminium wire is lighter than copper)

8. Calculate the resistance of copper tube 0.5cm thick and 2m long. The external diameter is

10cm. Given that the resistance of copper wire is 1 m long and 1mm2 in cross section is

1/58 Ω. (Ans. 23.11µΩ)

26-08-13

9. Each second 1017 electrons flow from right to left across a cross section of a wire attached

to the two terminals of a battery. Calculate the magnitude and direction of conventional

current in the wire. (Ans. 0.016A , left to right)

10. If a current of 2 A flows for 2 minutes, find the quantity of charge transferred.(240

coulombs)

11. Calculate the potential difference of an energy source that provides 50 mJ of energy

every for every micro coulomb of charge that flows. (Ans. 50000V )

12. A source of 5 V supplies a current of 3 A for a period of 10 minutes. How much energy

is provided in this time. (9000 J)

13. An electronic heater consumes 1.8 MJ of energy, when connected to a 250 V supply for

30 minutes. Find the power rating of the heater and the current taken from the supply.(1

kW, 4 A) . Hint: power =voltage×current.

14. Determine the resistance and the power dissipation of the resistor that must be placed in

series with 75 ohm resistor across 120V source in order to limit the power dissipation in

the 75 ohm resistor to 90W. (Ans. 34.6Ω, 41.5W)

15. Determine the current supplied by the source in the circuit of figure. (Ans. 28.44A)

16. (a) Consider a series–parallel combination of resistors as shown in Figure (a). Find the

equivalent resistance as seen from terminals A–B.

(b) Determine the current I and power P delivered by a 10-V dc voltage source applied at

terminals A–B, with A being at higher potential than B.

(c) Replace the voltage source by an equivalent current source at terminals A–B.

(d) Show the current and voltage distribution clearly in all branches of the original circuit

configuration. (Ans. 2Ω)

17. Find the unknown currents marked in figure shown. (Ans. I1=30A, I2=35A, I3=-90A,

I4=105A, I5=80A)

18. A 100V, 60W bulb is connected in series with a 100V, 100W bulb and the combination is

connected across 200V mains. Find the value of the resistance that should be connected

in parallel with the first bulb so that each bulb may get rated current at rated voltage.

(Ans. 250Ω)

19. Find the voltage drop across 1Ω resistor and power loss across 2Ω resistor. (Ans.

30.4W,2.21V)

20. Given the network in Figure, (a) Find the currents through resistors R1, R2, and R3. (b)

Compute the voltage V1. (c) Show that the conservation of power is satisfied by the

circuit.

21. Use delta–wye transformation for network reduction and determine the current through

the 12Ω resistor in the circuit of Figure. (Ans. 4.5A)

22. Calculate VAB for the network shown in Figure. (Ans. 3.5V)

23. Determine VAB in the network shown in Figure. (Ans. - 2V)

24. A network is arranged as in Fig. C. Calculate the equivalent resistance between (a) A and

B, and (b) A and N. ( Ans. 2.87ohm and 0.98 ohm)

1. (a) Calculate the reactance of a coil of inductance 0.32 H when it is connected to a 50 Hz supply. (b) A coil has a reactance of 124 ohm in a circuit with a supply of frequency 5 kHz. Determine the inductance of the coil. [100.5 ohm, 3.95 mH]

2. A coil has an inductance of 40 mH and negligible resistance. Calculate its inductive reactance and the resulting current if connected to (a) a 240 V, 50 Hz supply, and (b) a 100 V, 1 kHz supply. [12.57ohm, 19.09 A, 251.3 ohm, 0.398 A]

3. Determine the capacitive reactance of a capacitor of 10 μF when connected to a circuit of frequency (a) 50 Hz (b) 20 kHz [318.3 ohm, 0.796 ohm]

4. Given the sinusoid 5 sin( 4 Πt−60 )calculate its amplitude, phase, angular frequency, period, and frequency.[Answer: 5, -60, 12.57 rad/s, 0.5 s, 2 Hz.]

5. Calculate the current taken by a 23 μF capacitor when connected to a 240 V, 50 Hz supply. [1.73A]

6. In a series R–L circuit the p.d. across the resistance R is 12 V and the p.d. across the inductance L is 5 V. Find the supply voltage and the phase angle between current and voltage. [13 V, 22.37 lagging]

7. A coil has a resistance of 4 ohm and an inductance of 9.55 mH. Calculate (a) the reactance, (b) the impedance, and (c) the current taken from a 240 V, 50 Hz supply. Determine also the phase angle between the supply voltage and current [Ans: 3 Ohm, 5 Ohm, 48 A, 36.56 lagging]

8. Three circuits A,B and C are connected in series across a 200 V supply. The voltage across circuit A is 50 V lagging the supply voltage by 45 and circuit C is 100 V leading the supply voltage by 30. Determine the voltage across the circuit B and its phase relationship with supply voltage. [Ans: 79.4V, 10.38 lagging]

9. An e.m.f. of 200 V at a frequency of 2 kHz is applied to a coil of pure inductance 50 mH. Determine (a) the reactance of the coil, and (b) the current flowing in the coil. [628 ohm, 0.318A]

10. Two similar capacitors are connected in parallel to a 200 V, 1 kHz supply. Find the value of each capacitor if the circuit current is 0.628 A. [0.25 microF]

11. A voltage of 35 V is applied across a C–R series circuit. If the voltage across the resistor is 21 V, find the voltage across the capacitor. [28V]