Exercise [Resistors]

EXERCISE

1. A potential difference of 120 volts exists between the ends of a wire of 200 cm. Its diameter is 0.15 mm. The current flowing is 2.4 A. Calculate the resistivity.

[Ans: 0.442 × 10 2-m]

2. Three resistors 30 Ω,25 Ω and 45 Ω are connected in series across 200 V mains. Calculate (i) total resistance (ii) current (iii) pd across each element.

[Ans: 100 Ω, 2 A, 60 V, 50 V and 90V]

3. Calculate (i) equivalent resistance offered by the circuit to the voltage source. (ii) source current

 [Ans: 2.5 Ω, 20A]

4. Three resistors 2 Ω, 3 Ω and 4 Ω are in parallel. How will a total current of 8A be divided?

[Ans: 3.7 A, 2.46 A, 1.84 A]

5. What resistance must be connected in parallel with 10 Ω to give an equivalent resistance of 6 Ω?

[Ans: 15 Ω]

6. Two resistor R₁ and R₂ are connected in parallel and a voltage of 200V. d.c. is applied to the terminals. The total current drawn is 20A. R₁ = 30 Ω. Find R₂ and power dissipated in each resistor.

[Ans: R₂ = 1502 1333 watts, 2667 watts]

7. In the circuit find the currents in all the resistors. Also calculate the supply voltage.

 [Ans: I₂ 5A; I₅ =2A; I₁₀ = 1A; V = 130 volts]

8. Find the resistance between the terminals A and B.

 [Ans: 3 Ω]

9. Calculate the following for the circuit given

(i) Total resistance offered to source

(ii) Total current from the source

(iii) Power supplied by the source

 [Ans: 109, 10A, 1000 W]

10. A letter A is constructed of an uniform wire of 1 ohms resistance per cm. The sizes of the letter are 60 cm long and the cross piece is 30 cm long. Apex angle is 60°. Find the resistance of the letter between the two ends of the legs.

[Ans: 80 ohms]

11. A bulbs rated 110 V, 60 W is connected with another bulb rated 110 V, 100 W across 220 V mains. Calculate the resistance which should be shunted (parallel connection) with the first bulb so that both the bulbs may take their rated power.

[Ans: 302.5Ω ]

 12. Two resistors R₁ = 2500 Ω and R₂ = 4000 Ω are joined in series and connected to a 100 V supply. The voltage drop across R₁ and R₂ are measured successively by a volt meter having a resistance of 50000 Ω. Find the sum of the readings.

[Ans: 97 V]

13. Determine the value of R if the power dissipated in 10 ohm resistor is 90 W.

[Ans: 60 ]