UNIT-2 CURRENT ELECTRICITY

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1 UNIT-2 CURRENT ELECTRICITY 1 Marks Question 1. A wire of resistance R is cut into n equal parts.these parts are then connected in parallel with each other. The equivalent resistance of the combination is (a) nr (b) R/n (c) n/r 2 (d) R/n 2 2. What is meant by drift speed of free electrons? 3. Find the equivalent resistance between the points a and c of the given network of resistors. 4. If the potential difference applied across a variable resistor is constant, draw a graph between the current in the resistor and the resistance. 5. A part of an electric circuit is shown below (Figure): 6. In an electric dipole, what is the locus of a point of zero potential?

2 7. What is the colour code of a carbon resistor having a resistance of 470 ohm and a tolerance of 5%? 8. What is the resistance of a carbon resistor whose coloured bands are shown below: 9. Five resistors are connected as shown in figure. The effective resistance i.e. equivalent resistance between the points A and B is : (a) 4ohm (b) 5ohm (c) 15ohm (d) 20ohm 10. Current I flowing through a metallic wire of area of cross-section a is given by the equation I = naevd. What is the meaning of the symbols n and vd? 11. What is the ratio P1: P2 of electric power developed in R1 and R2 shown in Figure below? 12. Ohm s law in vector form: (a) J = ρe (b) J = σe

3 (c) E = ρj (d) V = IR 13. A carbon resistor has colored band as shown in figure below. The resistance of the resistor is: (a) 26Ω ± 10% (b) 26Ω ± 5% (c) 260Ω ± 10% (d) 260Ω ± 5% 14. On which conservation principle is Kirchhoff s Second Law of electrical networks based? 15. Which conservation principle is involved in Kirchoff s first law of electric circuit? 16. Figure I below shows five dc sources (cells). Their emf s are shown in the figure. Emf of the battery AB is: (A) 8V (B) 16V (C) 4V (D) 2V 17. Define temperature coefficient of resistance of the material of conductor.

4 18. Find the emf of the battery shown in figure: 19. For a metallic conductor, what is the relation between current density(j), conductivity (σ)and electric field intensity E? 20. A resistor R is connected to a cell of emf e and internal resistance r. Potential difference across the resistor R is found to the relation between e,v, R and r. 21. A 10m long potentiometer wire carries a steady current. A standard cell of emf V is balanced against a length of cm of the wire. What is potential gradient across the potentiometer wire? 22. Three identical cells each of emf 2V and internal resistance 1 ohm are connected in series to form a battery. The battery is then connected to a parallel combination of two identical resistors, each of 6 ohm. Find the current delivered by the battery. 23. In current electricity, ohm s law is obeyed by all: (A) Solids (B) Liquids (C) Gases (D) Metals 24. The equivalent resistance between points a and f of the network shown in figure is:

5 (a) 24 ohm (b) 110 ohm (c) 140 ohm (d) 200 ohm 25. In figure below, find the value of resistance X for which points A and B are the same potential: 2 Marks Question 26. When a potential difference of 3V is applied between the two ends of a 60cm long metallic wire, current density in it is found to be 1x10-7Am -2. Find conductivity of the material of the wire in SI system. 27. What is current density? Write the vector equation connecting current density J with electric field intensity E, for an ohmic conductor. 28. Two resistors R1=60 ohm and R2=90 ohm are connected in parallel. If electric power consumed by the resistor R1 is 15 W, calculate the power consumed by the resistor R A metallic wire has a resistance of 3 Ω at 0 o C and 4.8 Ω at 150 o C. Find the temperature coefficient of resistance of its material. 30. A current I flows through a metallic wire of radius r and the free electrons in it drift with a velocity V.Calculate the drift velocity of the free electrons through the wire of the same material, having double the radius, when same current flows through it. 31. Draw labelled graphs to show how electrical resistance varies with temperature for : (i) a metallic wire (ii) a piece of carbon.

6 32. With reference to free electron theory of counductivity, explain the terms: (i) Drift speed (ii) Relaxation time. 33. Two resistors R1=400ohm and R2=20 ohm are connected in parallel to a battery. If heating power developed in R1 is 25 W, find the heating power developed in R In the following circuit what must be the value of R such that the current in the 6 Ω resistance is zero? What is the current in 7Ω resistor at this value? 3 Marks Question 35. In the circuit shown below in figure, E1 and E2 are batteries having emfs 4 V and 3.5V respectively and internal resistance 1 ohm and 2 ohm respectively. Using kirchoff s laws, calculate currents: I1, I2 and I In the circuit shown below (Figure), PQ is a uniform metallic wire of length 4 m and resistance 20Ω. Battery B has an emf of 10V and internal resistance of 1Ω. J is a jockey or slide contact. Resistance of the ammeter A and connecting wires is negligible.

7 (i) When the jockey J does not touch the wire PQ, what is the reading of the ammeter A? (ii) Where should the jockey J be pressed on the wire PQ so that the galvanometer G shows no deflection? 37. In the circuit shown in Figure 4 below, E is a battery of emf 6 V and internal resistance 1 Ω. Find the reading of the ammeter A, if it has negligible resistance: 38. With the help of a labelled diagram, show that the balancing condition of a Wheatstone bride is: = where the terms have their usual meaning. 39. n cells, each of emf e and internal resistance r are joined in series to form a row. m such rows are connected in parallel to form a battery of N=mn cells. This battery is connected to an external resistance R. (i) What is the emf of this battery and how much is its internal resistance? (ii) Show that current I flowing through the external resistance R is given by: I = Ne mr + nr 40. In Figure below, find the reading of the voltmeter(v), having a resistance of 2000 ohm: 41. Draw a labelled circuit diagram of a potentiometer to measure internal resistance of a cell. Write the working formula.(derivation is not required)

8 42. A 10m long uniform metallic wire having a resistance of 20 ohm is used as a potentiometer wire. This wire is connected in series with another resistance of 480 ohm and a battery of emf 5V having negligible internal resistance. If an unknown emf e is balanced across 6m of the potentiometer wire, calculate: (i) the potential gradient across the potentiometer wire. (ii) the value of the unknown emf e. 43. Figure below shows two resistors R1 and R2 connected to a battery having an emf of 40V and negligible internal resistance. A voltmeter having a resistance of 300 ohm is used to measure potential difference across R. Find the reading of the voltmeter. 44. In a meter bridge circuit, resistance in the left hand gap is 2 ohm and an unknown resistance X is in the right hand gap as shown in figure below. The null point is found to be 40cm from the left end of the wire. What resistance should be connected to X so that the new null point is 50 cm from the left end of the wire?

9 45. In the circuit shown in figure below, E1 and E2 are two cells having emfs 2V and 3V respectively, and negligible internal resistances. Applying Kirchhoff Laws of electrical networks, find the values of currents I1 and I Draw a circuit diagram and explain the method for the determination of internal resistance of a cell using potentiometer. Derive the formula to be used. 47. Draw a labelled circuit diagram of a potentiometer to compare emfs of two cells. Write the working formula.(derivation not required) 48. In the circuit shown in figure, E1=17V, E2=21V, R1=2ohm, R2=3 ohm and R3=5ohm. Using kirchoff s laws, find the currents flowing through the resistors R1, R2 and R3. (Internal resistance of each of the batteries is neglegible.) 49. How much resistance should be connected to 15 ohm resistor shown in circuit in figure below so that the points M and N are at the same potential:

10 50. Apply Kirchoff s Laws to determine the currents I1 and I2 in the circuit shown in Figure below:

CHAPTER 3: ELECTRIC CURRENT AND DIRECT CURRENT CIRCUIT

CHAPTER 3: ELECTRIC CURRENT AND DIRECT CURRENT CIRCUIT PSPM II 2005/2006 NO. 3 3. (a) Write Kirchhoff s law for the conservation of energy. FIGURE 2 (b) A circuit of two batteries and two resistors is