Section A. Two resistors of 10 Ω and 15 Ω are connected in series to a battery of 6V. How can the values of current passing through them be compared?

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1 EXAM PRACTICE Past Year Board Questions CBSE-Class X Physics Electricity Section A (1 mark each) Question 1. Question 2. Question 3. Question 4. Question 5. Question 6. How is an ammeter connected in a circuit to measure current flowing through it? What happens to resistance of a conductor when its area of crosssection is increased? A given length of a wire is doubled on itself and this process is repeated once again. By what factor does the resistance of the wire change? Two resistors of 10 Ω and 15 Ω are connected in series to a battery of 6V. How can the values of current passing through them be compared? [Delhi 2009C] A wire of resistance 20 Ω is bent to form a closed square. What is the resistance across a diagonal of the square? [HOTS, AI 2009C] Study the following circuit and answer the question that follows: Question 7. (a) State the type of combination of the two resistors in the circuit. (b) How much current is flowing through (i) 10 Ω and through (ii) 20 Ω resistors? (c) What is the ammeter reading? [AI 2008C] Why is a series arrangement not used for connecting domestic electrical appliances in a circuit? [AI 2008]

2 Question 8. There are two electric bulbs (i) marked 60 W, 220 V and (ii) marked 100 W, 220 V. Which one of the two has a higher resistance? [Delhi 2006C] Question 9. Resistance of an incandescent filament of a lamp is comparatively much more than that when it is at room temperature. Why? Question 10. How does the resistance of an ohmic conductor depend on the applied voltage? Section B (2 marks each) Question 1. Question 2. Question 3. How does the resistance of an ohmic conductor depend on the applied How much current will an electric bulb draw from 220 V source if the resistance of the bulb is 1200 Ω? If in place of bulb, a heater of resistance 100 Ω is connected to the sources, calculate the current drawn by it. [CBSE (CCE) 2012] Draw a schematic diagrams of an electric circuit comprising of 3 cells and an electric bulb, ammeter, plug-key in the ON mode and another with same components but with two bulbs in parallel and a voltmeter across the combination. [CBSE (CCE) 2012] Out of the two wires X and Y shown below, which one has greater resistance? Justify your answer. [CBSE (CCE) 2012] Question 4. A 9 Ω resistance is cut into three equal parts and connected in parallel. Find the equivalent resistance of the combination. Question 5. An electric iron has a rating of 750 W, 220 V. Calculate the (i) current flowing through it, and (ii) its resistance when in use. [CBSE (CCE) 2011, Delhi 2007]

3 Question 6. (a) What do the following circuit symbols represent? (b) The potential difference between the terminals of an electric heater is 60 V when it draws a current of 4A from the source. Find the resistance of heater when in use. Question 7. Question 8. The charge possessed by an electron is 1.6 X coulombs. Find the number of electrons that will flow per second to constitute a current of 1 ampere. Explain the role of fuse in series with any electrical appliance in an electric circuit. Why should a fuse with defined rating for an electric circuit not be replaced by one with a larger rating? Question 9. The wattage of a bulb is 24 W when it is connected to a 12 V battery. Calculate its effective wattage if it operates on a 6 V battery (Neglect the change in resistance due to unequal heating of the filament in the two cases). Question 10. Consider the following circuit diagram. If R 1 = R 2 = R 3 = R 4 = R 5 = 3 Ω, find the equivalent resistance (R s ) of the circuit.

4 Question 11. In an experiment to study the relation between the potential difference across a resistor and the current through it, a student recorded the following observations: Potential difference V (volts) Current / (amperes) On examine the above observations, the teacher asked the student to reject one set of readings as the values were out of agreement with the rest. Which one of the above sets of readings can be rejected? Calculate the mean value of resistance of the resistor based on the remaining four sets of readings. [AI 2010] Question 12. Two students perform the experiments on series and parallel combinations of two given resistors R 1 and R 2 and plot the following V-1 graphs. Which of the two diagrams correctly represents the labels 'series and parallel' on the plotted curves? Justify your answer. [HOTS, CBSE Sample Paper 2009] Question 13. Question 14. Two metallic wires A and B of the same material are connected in parallel. Wire A has length l and radius r, wire B has a length 2l and radius 2r. Calculate the ratio of the equivalent resistance in parallel combination and the resistance of wire A [CBSE Sample Paper 2009] Draw a schematic diagram of an electric circuit consisting of a battery of five 2 V cells, a 20 Ω resistor, a 30 Ω resistor, a plug key, all connected in series. Calculate the value of current flowing through the 20 Ω resistor and the power consumed by the 30 Ω resistor. [AI 2009]

5 Question 15. Question 16. Question 17. Question 18. A piece of wire of resistance 20 Ω is drawn out so that its length is increased to twice its original length. Calculate the resistance of the wire in the new situation. [Delhi 2009] What is an electric circuit? Distinguish between an open and a closed circuit. [AI 2009] Two wires of equal lengths, one of copper and the other of manganin (an alloy) have the same thickness. Which one can be used for (i) electrical transmission lines (ii) electrical heating devices? Why? [Delhi 2008C] An electric lamp is marked 25 W, 220 V. It is used for 10 hours daily. Calculate (i) its resistance while glowing. (ii) energy consumed in kwh per day. [AI 2007] Question 19. (i) Draw a diagram to show how two resistors R 1 and R 2 are connected in series. (ii) In a circuit of two resistors, 5 Ω and 10 Ω are connected in series. How can the current passing through the two resistors be compared? [AI 2007] Question 20. Question 21. Question 22. In the given circuit, resistors A and B are made up of same metal and are of the same length but, A is thicker than B. of heat produced per second, in 4 Ω resistance if 10j heat is produced per second in 10 Ω resistor. 100 J of work is done in transferring 20 C of charge between two points in a conductor. Find the resistance offered by the conductor, if a current of 2A flows through it. You are given several identical resistors each having resistance of 10 Ω and a maximum current of 1A is allowed to pass through each resistor. It is required to make a suitable combination of these resistances of 5 Ω which can carry a current of 4A. Find the number of such resistances that will be required.

6 Question 23. Question 24. Question 25. Compute the heat generated while transferring C of charge in one hour through a potential difference of 50 V Will current flow more easily through a thick wire or through a thin wire of the same material when connected to the same source? Why? A piece of wire of resistance R is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R', then find the ratio RIR'. Section C (3 marks each) Question 1. Question 2. Question 3. Question 4. Question 5. Two identical wires one of nichrome and other of copper are connected in series and a current (/) is passed through them. State the change observed in the temperatures of the two wires. Justify your answer. State the law which explains the above observation. [CBSE (CCE) 2012] An electric bulb is rated at 60 W, 240 V. Calculate its resistance. If the voltage drops to 192 V, calculate the power consumed and the current drawn by the bulb. (Assume that the resistance of the bulb remain unchanged) [CBSE (CCE) 2012] A torch bulb is rated 2.5 V and 750 rna. Calculate (i) its power, (ii) its resistance and (iii) the energy consumed, if this bulb is lighted for four hours. Series arrangements are not used for domestic circuits. List any three reasons. Name the physical quantity which is (i) same (ii) different in all the bulbs when three bulbs of: (a) (b) (c) (d) same wattage are connected in series. same wattage are connected in parallel. different wattage are connected in series. different wattage are connected in parallel.

7 Question 6. Two devices of rating 44 W, 220V and 11 W, 220 V are connected in series. The combination is connected across a 440 V mains. The fuse of which of the two devices is likely to burn when the switch is ON? Justify your answer. Question 7. Five resistors are connected in a circuit as shown. Find the ammeter reading when circuit is closed. Question 8. Study the circuit shown in which three identical bulbs B 1, B 2 and B 3 are connected in parallel with a battery of 4.5 V. (i) What will happen to the glow of other two bulbs if the bulb B 3 gets fused? (ii) If the wattage of each bulb is 1.5 W, how much reading will the ammeter A show when all the three bulbs glow simultaneously? (iii) Find the total resistance of the circuit.

8 Question 9. A circuit is shown in the diagram given below. (a) Find the value of R. (b) Find the reading of the ammeter. (c) Find the potential difference across the terminals of the battery. Question 10. Consider the circuit shown in the diagram. Find the current in 3Ω resistor

9 Question 11. Study the 1-V graph for four conductors A, B, C and D having resistance R A, R B, R C and R D respectively, and answer the following questions: (i) (ii) (iii) (iv) Which one of these is a best conductor? If all the conductors are of same length and same material, which is the thickest? If all the conductors are of same thickness and of same material, which is the longest? If the dimensions of all the conductors are identical, but their materials are different which one would you use as (a) resistance wire (b) connecting wire? (v) (vi) Which one of the following relations is true for these conductors? (a) R A > R B > R C > R D (b) R A < R B < R C < R D (c) R A = R B = R C = R D (d) R A = R B < R C < R D If conductors A and B are connected in series and 1-V graph is plotted for the combination, its slope would be (a) less than that of A. (b) more than that of A. (c) between A and B. (d) more than that of D. (vii) If conductors C and D are connected in parallel and I-V graph is plotted for the combination, its slope would be (a) lesser than that of A. (b) more than that of D. (c) between C and D. (d) between B and C.

10 Question 12. Two resistors with resistances 5 Ω and 10 Ω are to be connected to a battery of emf 6 V so as to obtain: (i) minimum current (ii) maximum current (a) How will you connect the resistances in each case? (b) Calculate the strength of the total current in the circuit in the two cases. [HOTS, Delhi 2009] Question 13. (a) Define the term 'volt'. (b) State the relation between work, charge and potential difference for an electric circuit. Calculate the potential difference between the two terminals of a battery if 100 J of work is required to transfer 20 C of charge from one terminal of the battery to the other. [AI 2009] Question 14. (a) Define the term 'coulomb'. (b) State the relationship between the electric current, the charge moving through a conductor and the time of flow. Calculate the charge passing through an electric bulb in 20 minutes if the value of current is 200 rna. [AI 2009] Question 15. (a) How is the direction of electric current related to the direction of flow of electrons in a wire? (b) Calculate the current in a circuit if 500 C of charge passes through it in 10 minutes. [AI 2009] Question 16. Two lamps, one rated 60 W at 220 V and the other 40 W at 220 V, are connected in parallel to the electric supply at 220 V. (a) (b) (c) Draw a circuit diagram to show the connections. Calculate the current drawn from the electric supply. Calculate the total energy consumed by the two lamps together when they operate for one hour. [AI 2008]

11 Question 17. In a circuit shown below calculate: (a) total resistance in the arm CE, (b) total current drawn from the battery, and (c) current in each arm, i.e., AB and CE of the circuit. [HOTS, AI 2006] Question 18. Question 19. Name the unit used in selling electrical energy to consumers. Two lamps, one rated 100 W at 220 V and the other 40 W at 220 V are connected in parallel to a 220 V mains supply. Calculate the electric current drawn from the supply line. [Foreign 2009] Study the circuit shown below: A current of 0.6 A is shown by ammeter in the circuit when the key K 1 is closed. Find the resistance of the lamp L. What change in current flowing through the 5 Ω resistor and potential difference across the lamp will take place, if the K 2 key is also closed? Give reason for your answer.

12 Question 20. Find the equivalent resistance across the two ends A and B of this circuit. Question 21. Calculate the electric current in the given circuit when (i) (ii) (iii) key K 1 is open and is closed both the keys are closed K 1 is closed and is open

13 Question 22. Find the equivalent resistance across the two ends A and B of the following circuits. (ii) Assume that P and Q are at the same potential. Question 23. Show how would you connect three resistors, each of resistance 6 Ω, so that the combination has a resistance of (i) 9 Ω (ii) 4 Ω Question 24. Several electric bulbs designed to be used on a 220 V electric supply line, are rated 10 W. How many lamps can be connected in parallel with each other across the two wires of 220 V line if the maximum allowed current is 5 A? Question 25. A hot plate of an electric oven connected to 220 V line has two resistance coils A and B, each of 24 Ω resistance, which may be used separately, in series, or in parallel. What are the currents in the three cases?

14 Section D (5 marks each) Question 1. Three bulbs each having power P are connected in series in an electric circuit. In another circuit, another set of three bulbs of same power are connected in parallel to the same source. (i) (ii) (iii) Will the bulbs in both the circuits glow with the same brightness? Justify your answer. Now let one bulb in each circuit get fused. Will the rest of the bulbs continue to glow in each circuit? Give reason. Representing each bulb by a resistor, draw circuit diagram for each case. [HOTS, CBSE (CCE) 2012] Question 2. (a) Though same current flows through. The electric line wires and the filament of bulb, yet only the filament glows. Why? (b) (c) (d) The temperature of the filament of bulb is 2700 o C when it glows. Why does it not get burnt up at such high temperature? The filament of an electric lamp, which draws a current of 0.25 A is used for four hours. Calculate the amount of charge flowing through the circuit. An electric iron is rated 2 kw at 220 V. Calculate the capacity of the fuse that should be used for the electric iron. [CBSE (CCE) 2012]

15 Question 3. (a) In the given circuit, connect a nichrome wire of length 'L' between points X and Y and note the ammeter reading. (i) (ii) (b) When this experiment is repeated by inserting another nichrome wire of the same thickness but twice the length (2L), what changes are observed in the ammeter reading? State the changes that are observed in the ammeter reading if we double the area of cross section without changing the length in the above experiment. Justify your answer in both the cases. "Potential difference between points A and B in an electric field is 1 V". Explain the above statement. [CBSE (CCE) 2012] Question 4. Question 5. Explain with the help of a labelled circuit diagram, how will you find the resistance of a combination of three resistors, of resistance R 1, R 2 and R 3, joined in parallel. Also mention how will you connect the ammeter and the voltmeter in the circuit while measuring the current in the circuit and the potential difference across one of the three resistors of the combination. [Delhi 2010] Derive the expression for the heat produced due to a current 'F flowing for a time interval 't' through a resistor 'R' having a potential difference 'V' across its ends. With which name is the relation known? How much heat will an instrument of 12 W produce in one minute if it is connected to a battery of 12 V? [Delhi 2010]

16 Question 6. Deduce the expression for the equivalent resistance of the parallel combination of three resistors R 1, R 2 and R 3 Consider the following electric circuit: (a) Which two resistors are connected in series? (b) Which two resistors are connected in parallel? (c) If every resistor of the circuit is of 2 Ω, what current will flow in the circuit? [HOTS, Foreign 2010] Question 7. In a household electric circuit, different appliances are connected in parallel to one another. Give two reasons. An electrician puts a fuse of rating 5 A in that part of domestic electrical circuit in which an electrical heater of rating 1.5 kw, 220 V is operating. What is likely to happen in this case and why? What change, if any, needs to be made? [HOTS, CBSE Sample Paper 2009] Question 8. (a) Two resistors R 1 and R 2 may form (i) a series combination or (ii) a parallel combination, and the combination may be connected to a battery of 6 volts. In which combination, will the potential difference across R 1 and across R 2 be the same and in which combination, will the current through R 1 and through R 2 be the same? (b) For the circuit shown in this diagram, calculate (i) (ii) (iii) the resultant resistance. the total current. the voltage across 7Ω resistor. [Foreign 2009]

17 Question 9. (a) Name an instrument that measures electric current in a circuit. Define the unit of electric current. (b) What do the following symbols mean in circuit diagrams? (c) (i) An electric circuit consisting of a 0.5 m long nichrome wire XY, an ammeter, a voltmeter, four cells of 1.5 V each and a plug key was set up. Draw a diagram of the electric circuit to study the relation between the potential difference maintained between the points 'X' and 'Y' and the electric current flowing through XY (ii) Following graph was plotted between V and I values: What would be the values of 0.8 V, 1.2 V and 1.6 V respectively? What conclusion do you draw from these values? ratios when the potential difference is [Delhi 2008] Question 10. (a) Define SI unit of resistance. (b) Write any three differences between the series and parallel combination of resistance. (c) A set of 'n' identical resistors each of resistance R are connected in series and the effective resistance is found to be 'X'. When these 'n' resistors are connected in parallel, the effective resistance is found to be 'Y'. Find the ratio of X and Y.

18 Question 11. (a) Find the value of current I in the circuit given below: (b) You have four resistors of 8 Ω each. Show how would you connect these resistors to have effective resistance of 8 Ω.