NUMERICALS BASED ON ELECTRICITY

Q.1. What will be the current drawn by an electric bulb of 40 W when it is connected to a source of 220V?

Q.2. A bulb is rated as 250V; 0.4A. Find its power and resistance.

Q.3. An electric bulb is connected to a 220V power supply line. If the bulb draw a current of 0.5A, calculate the power of the bulb.

Q.4. An electric bulb is connected to a 250 V generator. The current is 0.50 A. What is the power of the bulb?

Q.5. What current will be taken by a 920W appliance if the supply voltage is 230V?

Q.6. When an electric lamp is connected to 12V battery, it draws a current 0.5A. Find the power of the lamp.

Q.7. Calculate the power used in 2 resistor in each (i) a 6V battery in series with 1Ω and 2Ω resistor (ii) a 4V battery in parallel with 12Ω and 2Ω resistor.

Q.8. A 100 W electric light bulb is connected to a 250 V supply. Determine (a) the current flowing in the bulb, and (b) the resistance of the bulb.

Q.9. Calculate the power dissipated when a current of 4 mA flows through a resistance of 5 kΩ

Q.10. An electric kettle has a resistance of 30Ω. What current will flow when it is connected to a 240 V supply? Find also the power rating of the kettle.

Q.11. A current of 5 A flows in the winding of an electric motor, the resistance of the winding being 100Ω. Determine (a) the p.d. across the winding, and (b) the power dissipated by the coil.

Q.12. The current/voltage relationship for two resistors A and B is as shown in below Figure. Determine the value of the resistance of each resistor and also find the power dissipated through each resistor.

Q.13. The hot resistance of a 240 V filament lamp is 960Ω. Find the current taken by the lamp and its power rating.

Q.14. A 12 V battery is connected across a load having a resistance of 40Ω. Determine the current flowing in the load, the power consumed and the energy dissipated in 2 minutes.

Q.15. A source of e.m.f. of 15 V supplies a current of 2 A for six minutes. How much energy is provided in this time?

Q.16. Electrical equipment in an office takes a current of 13 A from a 240 V supply. Estimate the cost per week of electricity if the equipment is used for 30 hours each week and 1 kWh of energy costs 7p

Q.17. An electric heater consumes 3.6 MJ when connected to a 250 V supply for 40 minutes. Find the power rating of the heater and the current taken from the supply.

Q.18. Determine the power dissipated by the element of an electric fire of resistance 20 when a current of 10 A flows through it. If the fire is on for 6 hours determine the energy used and the cost if 1 unit of electricity costs 7p.

Q.19. A business uses two 3 kW fires for an average of 20 hours each per week, and six 150 W lights for 30 hours each per week. If the cost of electricity is 7p per unit, determine the weekly cost of electricity to the business.

Q.20. If 5 A, 10 A and 13 A fuses are available, state which is most appropriate for the following appliances which are both connected to a 240 V supply (a) Electric toaster having a power rating of 1 kW (b) Electric fire having a power rating of 3 kW

Q.21. The hot resistance of a 250 V filament lamp is 625 . Determine the current taken by the lamp and its power rating.

Q.22. Determine the resistance of a coil connected to a 150 V supply when a current of (a) 75 mA (b) 300 μA flows through it. Determine the power dissipated through it.

Q.23. Determine the resistance of an electric fire which takes a current of 12A from a 240 V supply. Find also the power rating of the fire and the energy used in 20 h.

Q.24. Determine the power dissipated when a current of 10 mA flows through an appliance having a resistance of 8 kΩ.

Q.25. 85.5 J of energy are converted into heat in nine seconds. What power is dissipated?

Q.26. A current of 4 A flows through a conductor and 10 W is dissipated. What p.d. exists across the ends of the conductor?

Q.27. Find the power dissipated when:

(a) a current of 5 mA flows through a resistance of 20 kΩ

(b) a voltage of 400 V is applied across a 120 kΩ resistor

(c) a voltage applied to a resistor is 10 kV and the current flow is 4 mA.

Q.28. A battery of e.m.f. 15 V supplies a current of 2 A for 5 min. How much energy is supplied in this time?

Q.29. In a household during a particular week three 2 kW fires are used on average 25 h each and eight 100 W light bulbs are used on average 35 h each. Determine the cost of electricity for the week if 1 unit of electricity costs 7p.

Q.30. Calculate the power dissipated by the element of an electric fire of resistance 30 when a current of 10 A flows in it. If the fire is on for 30 hours in a week determine the energy used. Determine also the weekly cost of energy if electricity costs 7.2p per unit.

Q.31. A television set having a power rating of 120 W and electric lawnmower of power rating 1 kW are both connected to a 240 V supply. If 3 A, 5 A and 10 A fuses are available state which is the most appropriate for each appliance.

Q.32. For a heater rated at 4kW and 220V, calculate: (a) the current (b) the resistance of the heater (c) the energy consumed in 2 hours and (d) the cost if 1kWh is priced at Rs. 4.60

Q.33. A radio set of 60W runs for 50hrs. How much electrical energy consumed?

Q.34. A current of 4A flows through a 12V can headlight bulb for 10min. How much energy transfer occurs during this time?

Q.35. Calculate the energy transferred by a 5A current flowing through a resistor of 2 for 30min.

Q.36. A bulb is rated at 200V-100W. What is its resistance? 5 such bulbs burn for 4 hrs. What is the electrical energy consumed? Calculate the cost if the rate is Rs. 4.60 per unit.

Q.37. A refrigerator having a power rating of 350W operates for 10hours a day. Calculate the cost of electrical energy to operate it for a month of 30days. The rate of electrical energy is Rs. 3.40 per KWh.

Q.38. What will be the current drawn by an electric bulb of 40W when it is converted to a source of 220V?

Q.39. An electric bulb is rated 220V and 100W. When it is operated on 110V, find the power consumed.

Q.40. An electric heater draws a current of 10A from a 220V supply. What is the cost of using the heater for 5 hrs everyday for 30days if the cost of 1 unit is Rs. 5.20?

Q.41. In house two 60W electric bulbs are lighted for 4 hrs and three 100W bulbs for 5 hrs everyday. Calculate the electrical energy consumed in 30days.

Q.42. An electric motor takes 5A current from a 220V supply line. Calculate the power of the motor and electrical energy consumed by it in 2 hrs.

Q.43. 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?

Q.44. An electric refrigerator rated 400 W operates 8 hour/day. What is the cost of the energy to operate it for 30 days at Rs. 3.00 per kWh?

Q.45. An electric motor takes 5 A from a 220 V line. Determine the power of the motor and the energy consumed in 2 h.

Q.46. Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to electric mains supply. What current is drawn from the line if the supply voltage is 220 V?

Q.47. Which uses more energy, a 250 W TV set in 1 hr, or a 1200 W toaster in 10 minutes?

Q.48. Two bulbs A and B are rated 100W – 120V and 10W – 120V respectively. They are connected across a 120V source in series. Which will consume more energy.

Q.49. Two bulbs A and B are rated 100W – 120V and 10W – 120V respectively. They are connected across a 120V source in series. Find the current in each bulb. Which will consume more energy.

Q.50. An electric kettle is rated at 230V, 1000W. What is the resistance of its element? What maximum current can pass through its element?

Q.51. An electric geyser has the rating 1000W, 220V marked on it. What should be the minimum rating in whole number of a fuse wire that may be required for safe use with this geyser?

Q.52. The mains power supply of a house is through a 5A fuse. How many 100W, 220V bulbs can be used in this house at the correct voltage?

Q.53. An electrician puts a fuse of rating 5A in that part of domestic electrical circuit in which an electrical heater of rating 1.5kW, 220V is operating. What is likely to happen in this case and why? What change if any needs to be made/

Q.54. Two bulbs of ratings 40W-220V and 60W-220V are connected in series and this combination is connected with a supply of 220V. Calculate the current from the supply line.

Q.55. Two bulbs have the ratings 40W-200V and 20W-110V. What is the ratio of their resistances?

Q.56. I can spend Rs. 9 per month (30days) on electric light. If power is 30paise per kWh and I use 5 identical bulbs for 5 hours a day, what should be the power of each bulb?

Q.57. Compute the number of electrons passing through per minute through an electric bulb of 60W, 220V.

Q.58. If electrical energy costs Rs.3 per unit, what is the total cost of leaving 4 light bulb rated at 100W each switched on for 8 hours.

Q.59. An electric heater of resistance 8Ω draws 15 A from the service mains 2 hours. Calculate the rate at which heat is developed in the heater.

Q.60. 100 J of heat are produced each second in a 4 Ω resistance. Find the potential difference across the resistor.

Q.61. Compute the heat generated while transferring 96000 coulomb of charge in one hour through a potential difference of 50 V.

Q.62. An electric iron of resistance 20 Ω takes a current of 5 A. Calculate the heat developed in 30 s.

Q.63. A p.d. of 250V is applied across a resistance of 500 Ω in an electric iron. Calculate (i) current (ii) heat energy produced in joules in 10s.

Q.64. Calculate the heat produced when 96000C of charge is transferred in 1 hour through a p.d. of 50V.

Q.65. A resistance of 40 Ω and one of 60 Ω are arranged in series across 220V supply7. Find the heat in joules produced by this combination of resistances in half a minute?

Q.66. When a current of 4A passes through a certain resistor for 10min, 2.88 x 104 J of heat are produced. Calculate (a) power of the resistor (b) the voltage across the resistor.

Q.67. A heating coil has a resistance of 200 Ω. At what rate will heat be produced in it when a current of 2.5 Ω flows through it.

Q.68. An electric heater of resistance 8 Ω takes a current of 15A from the mains supply line. Calculate the rate at which heat is developed in the heater.

Q.69. A resistance of 25 Ω is connected to a 12V battery. Calculate the heat energy in joule generated per minute.

Q.70. How much heat will an instrument of 12W produce in one minute if its is connected to a battery of 12V?

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Test Series for CBSE Term 1 Examination for Class 9 to 12

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