PHYSICS ELECTRICITY ASSIGNMENT 1

Transcription

1 PHYSICS ELECTRICITY ASSIGNMENT 1 1. What does an electric circuit mean? 2. Define the unit of electric current. 3. Calculate the number of electrons in 1 coulomb of charge. 4. Name a device used to maintain potential difference across a conductor. 5. What is meant by saying that the potential difference between 2 points is 1 V? 6. How much energy is given to each coulomb of charge passing through a 6 V battery? 7. On what factors does the resistance of a conductor depend? 8. Will current flow more easily through a thick wire or a thin wire of the same material, when it is connected to the same source? Why? 9. Let the electrical resistance of an electrical component remain constant while the potential difference across the two ends decreases to half its former value. What change will occur in the current through it? 10. Why are coils of electric toasters and irons made of an alloy rather than of a pure metal? 11. A current of 0.5 A is drawn by a filament of an electric bulb for 10 minutes. Find the amount of electric charge that flows through the circuit. 12. How much work is done in moving a charge of 2 C across two points having a potential difference 12 V? 13. (a) How much current will an electric bulb draw from a 220 V source, if the resistance of the bulb filament is 1200 Ω?(b) How much current will an electric heater coil draw from a 220 V source, if the resistance of the heater coil is 100 Ω? 14. The potential difference between the terminals of an electric heater is 60 V when it draws a current of 4 A from the source. What current will the heater draw if the potential difference is increased to 120 V? 15. Resistance of a metal wire of length 1 m is 26 Ω at 20 C. If the diameter of the wire is 0.3 mm, what will be the resistivity of the metal at that temperature? 16. A wire of given material having length l and cross-section A has a resistance of 4 Ω. What would be the resistance of another wire of the same material having length l/2 and area of cross-section 2A? 17. An electric lamp, whose resistance is 20 Ω, and a conductor of 4 Ω resistance are connected to a 6 V battery. Calculate (a) the total resistance of a circuit, (b) the current through the circuit, and (c) the potential difference across the electric lamp and conductor. 18. In the circuit diagram given in Fig 12.10, suppose the resistors, R 1, R 2 and R 3, have the values, 5 Ω, 10 Ω, 30 Ω, respectively, which have been connected to a battery of 12 V. Calculate (a) the current through each resistor, (b) the total current in the circuit, and (c) the total circuit resistance.

2 19. If in Fig 12.12,R 1 = 10 Ω, R 2 = 40 Ω, R 3 = 30 Ω, R 4 = 20 Ω, R 5 = 60 Ω, and a 12 V battery is connected to the arrangement. Calculate (a) the total resistancein the circuit, and (b) the total current flowing through the circuit. 20. An electric iron consumes energy at a rate of 840 W when heating is at the maximum rate and 360 W when the heating is at the minimum. The voltage is 220 V. What are the current and the resistance in each case? J of heat is produced each second in a 4 Ω resistance. Find the potential difference across the resistor. 22. An electric bulb is connected to a 220 V generator. The current is 0.50 A. What is the power of the bulb? 23. An electric refrigerator rated 400 W operates 8 hours/day. What is the cost of the energy to operate it for 30 days at 3.00 per kw h? S.B.O.A SCHOOL & JUNIOR COLLEGE CHENNAI 101 STD : X ELECTRICITY ASSIGNMENT 2 1. Calculate the amount of work done to carry 4 C of charge from a point at 100 V to a point at 120 V (Formula : W = Q V ){Ans: 80 J} 2. What is the resistance of an electric arc lamp when hot, if the lamp uses 20 A when connected to a 220 Volt line? (Formula : R = V/I) {Ans : 11 Ω } 3. Calculate the potential difference required across a conductor of resistance 5Ω to make a current of 1.5 Α flow through it. (Formula: V = I R ) {Ans : 7.5 V } 4. A torch bulb when cold has 1 Ω resistance. It draws a current of 3.0 A when glowing from a source of 3 V. Calculate the resistance of the bulb when glowing and explain the reason for the difference in resistance.

3 (Formula : R = V / I ) {Ans: 10 Ω } 5. How much current does an electric heater draw from a 220 V line, if the resistance of the heater is 50 Ω? { Ans: 4.4 A } 6. Find the Answer: S. No. V (Volt) I ( Ampere) R (Ω) 1.? ? A? ? ? S.B.O.A School & junior college -chennai 101 Physics Electicity Assignment-4 An electric mortor takes 5A from an source of 220v. Determine the power of the mortor and energy consumed in 2 hrs. What determines the rate in which energy is delivered by a current?.

4 An electric iron of resistance 20ohm takes a current of 5A. Calculate the heat developed in 30s compute the heat generated by transfering 96000coulomb of charge in one hour through a potential difference of 50V. What does the cord of an electric heater not glow while the heating element does What is (a)the highest,(b) the lowest total resistance that can be secured by combinations of four coils of resistance 4ohm,8ohm.12ohm.24ohm? How can three resistors of resistances2ohm,3ohm,and 6ohm be connected to give a total resistance of a)4 ohm b)1ohm? What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series? 100J of heat is produced eachsecoond in a 4 ohmresistance.find the potential diiference across the reistor.

5 PHYSICS STD - X ELECTRICITY ASSIGNMENT Name the factors that the electrical resistivity of a given wire depends. 2. What is the maximum resistance which can be made using 5 resistors each of (1/5)? 3. What is the minimum resistance which can be made using 5 resistors each of (1/5)? 4. An electric kettle consumes 1kw of electric power when operated at 220V. A fuse wire of what rating must be used for it? 5. How will you conclude that the same potential difference (voltage) exists across 3 resistors connected in a parallel arrangement to a battery? 6. What is Joule s heating effect? List the 4 applications in daily life. 7. When a 12 V battery is connected across an unknown resistor there is a current of 2.5mA in the circuit. Find the value of the resistance of the resistor. 8. A battery of 9V is connected in series with resistors of 0.2, 0.3, 0.4, 0.5 and 0.12 respectively. How much current would flow through the 12 resistor 9. How many 176 resistors (in parallel) are required to carry 5A on 220V line? 10. Show how you would connect three resistors each of resistance 6 so that the combination has a resistance of (i)9 (ii)4 11. Several electric bulbs designed to be used on a 220V electric supply line are rated 10W. How many lamps can be connected in parallel with each other across the two wires of 220 V line if the maximum allowable current is 5 A? 12. A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B, each of 24resistance, which may be used separately, in series or in parallel. What are the currents in the three cases? 13. Compare the power used in the 2 resistor in each of the following circuits: (i) a 6 V battery in series with 1 and 2 resistors, and (ii) 4 V battery in parallel with 12 and 2 resistors. 14. Two lamps, one rated 100 W at 220 V, and the other 60 W at 220V, are connected in parallel to electric mains supply. What current is drawn from the line if the supply voltage is 220 V? 15. Which uses ore energy, a 250 W TV set in 1 hour or a 1200 W toaster in 10 minutes? 16. An electric heater of resistance 8draws 15A from the service mains 2 hours. Calculate the rate at which heat is developed in the heater. 17. Explain the following. a) Why is the tungsten used almost exclusively for filament of electric lamps? b) Why are the conductors of electric heating devices, such as bread toasters and electric irons, made often alloy rather than a pure metal? c) Why is the series arrangement not used for domestic circuits? d) How does the resistance of a wire vary with its area of cross section? e) Why are copper and aluminum wires usually employed for electricity transmission?