VERY SHORT AND SHORT-ANSWERS QUESTIONS 46 Name the metal which has the lowest resistivity? 47 Define conductance 48 Of metals and alloys, which have greater value of temperature coefficient of resistance? (AISSCE 1995 C) 49 How does the conductivity of a semiconductor change with rise in temperature? (AISSCE 1994) 50 Connecting wires are made of copper Why? 51 A carbon resistor of 74 kΩ is to be marked with rings of different colours for its identification Write the sequence of colours (AISSCE 1994) 52 Calculate the equivalent resistance between the points X and Y: 2Ω X 3Ω Y 2Ω Fig A.1 53 A battery of emf E and internal resistance r is connected across a resistor R A current I flows in circuit Derive a relation between I, E, r and R (AISSCE 1992) 54 Outline the principle of a potentiometer 55 Which is more accurate – a voltmeter or a potentiometer? 56 Why are safety fuses connected in electric circuits and instruments? 57 Why copper wire is not used in a potentiometer? 58 What is the principle on which Kirchhoff’s first law is based? S Chand & Company Limited 59 State the working principle of a wheatstone bridge 60 What is the use of a meter bridge? 61 Three resistances R1, R2 and R3 are connected in series What is the equivalent resistance? 62 Three resistances R1, R2 and R3 are connected in parallel What is the equivalent resistance? 63 A Potentiometer of long wire is used for accurate measurement Why? 64 Name any one material having a small value of temperature coefficient of resistance Write one use of this material 65 Give three resistors each of resistance R, how will you combine them to have (i) maximum resistance, (ii) minimum resistance? What is the ratio of the maximum to the minimum resistance? 66 Calculate the equivalent resistance between the points A and C in the given network: D C 4Ω 2Ω 2Ω A 4Ω B Fig A.2 67 You are given three resistance of 1Ω, 2Ω and 3Ω How will you combine them to get an equivalent resistance of (i) 6Ω and (ii) 6/11Ω? S Chand & Company Limited 68 State Kirchhoffs’ laws (AISSCE 1990, 92, 93, Delhi 96) 69 Using colour code system find the resistance of the following carbon resistor: 1234 Yellow Violet Red Silver Fig A.3 70 71 72 73 What is the difference between emf and potential difference of a cell? What is steady current? Show it graphically against time? n cells, each of emf E, are connected in series What is the effective emf of the combination? n cells, each of emf E, are connected in parallel What is the effective emf of the combination? 74 A number of cells, each of emf E and internal resistance r, are to be connected across an external resistance R If R >> r, then which of the two modes–all cells in series or all cells in parallel – will give larger current? 75 In the above question if R