Question Bank on Ch-Electricity 1. (a) Define the S.I unit of potential difference. (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. (a) It is volt. When 1 joule of work is done in carrying 1 coulomb of charge, from infinity to a point in the electric field, then potential at that point is called 1 volt. (b) Potential difference, V = Work done on unit charge =W/q Work is 100 J,q=20C Potential difference, V=W/q=100/20=5V 2. (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 ma. (a) When 1 A current flows across the wire in 1 second, the charge transfer across its ends is said to be 1 coulomb. (b) The relationship between the electric current I, the charge q and time t is I=Q/t 3. (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. Ans(a) Conventional direction of electric current is opposite to the direction of flow of electrons in a wire. (b) q = 500 C, t = 10 X 60 = 600 s I = 500/600 = 5/6A 4. Define the S.I. unit of current.
Ans. The unit of current is Ampere. 1 Ampere is defined as current produced when 1 coulomb of charge flow through the cross section of a conductor in 1 second. 5. Define electric current. Ans: Electric current is defined as the flow of electric charges per unit time through a crosssection of a conductor. I= Q/t 6. Calculate the number of electrons constituting one coulomb of charge. Ans. 1C = 6 10 18 electrons. Q=ne Q=1C, e=1.6 x 10-19, n=? 7. Define 1 coulomb. 1 C is the charge that flows through a cross section of a conductor when 1 A of current passes in 1 Sec 8. A conductor carries a current of 0.2 A. Find the amount of charge that will pass through the cross-section of the conductor in 30 s. How much electrons will flow in this time interval if the charge on one electron is 1.6 x 10-19 9. The filament of an electric lamp draws a current of 0.4 A which lights for 3 hours. Calculate the amount of charge that flows through the circuit. 10. Calculate the current in the wire if 150 C charge is passed through it in 5 mins. 11. n electrons flow through a cross-section of a conductor in time t. If the charge on electron is e. Write an expression for the current in the conductor. 12. What do you mean by Electric potential difference? Electric potential difference between two points in an electric circuit carrying current is the amount of work done to move a unit charge from one point to another. Potential difference between two points = work done/ Charge V= W/Q 10. Define 1V. One volt is the potential difference between two points in a current carrying conductor when 1 joule of work is done to move 1 coulomb of charge from one point to another. 1 V = 1 J/C 13. How much energy is given to each coulomb of charge passing through a 6V battery? 14. How much work is done in moving a charge of 2 C across two points having potential difference of 12 V?
15. Calculate the amount of work done to carry 4 C of charge from a point at 100 V to a point at 120V. 16. What is electric circuit? Differentiate between open and closed circuit. A source of electric power (battery or cell), loads, switches and other elements connected together by wires form an electric circuit. Open circuit: key is open ( ), no flow of current, no potential difference is developed between two points in the circuit Close Circuit: key is closed (.), current flows continuously, potential difference is developed between two points in the circuit 17. 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. 18. 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: 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.
The third reading for V = 3.0 volt and I 0.6 A will be rejected as it has larger deviation from the rest of the readings. The value of resistance in the other four observations will be I (using R = V/I) 10Ω, 11 Ω, 10 Ω and 10.67 Ω. So, the mean value of resistance = 41.67/4 = 10.417 = 10.42 Ω 19. The charge possessed by an electron is 1.6 X 10-19 coulombs. Find the number of electrons that will flow per second to constitute a current of 1 ampere. 20.a) What do the following circuit symbols represents (b) The potential difference between the terminals of an electric heater is 60 V when it draws a current of 4 A from the source. Find the resistance of heater when in use. (a) (i) Wires crossing without touching each other. (ii) Rheostat/Variable resistor (b) Given: V = 60 V, I = 4 A, R =? From Ohm s law, V = IR 60 = 4 x R = 15 Ω 21. 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?
Length becomes one-fourth of the original length and area of cross-section becomes four times that of original Let the original Length and area be L1 and A1 and and New length and area be L2 and A2 respectively 22. How much current will an electric bulb draw from 220 V source if the resistance of the bulb is 1200Ω? If in place of bulb, a heater of resistance 100 Ω is connected to the sources, calculate the current drawn by it.