| Previous Year Questions of March Examinations from 2010 to 2020 |
| Chapter Name: CURRENT ELECTRICITY |
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Copper is one of the suitable materials to make connecting wires due its low resistivity. a) What do you mean by resistivity? b) A copper wire is the form of a cylinder and has a resistance R. It is stretched till its thickness reduces by half of its initial size. Find its new resistance in terms of R. |
| A potentiometer wire PQ of length 1 meter is connected to a standard cell of EMF E1 . Another cell E2 of EMF 1.02 volt is connected to a parallel combination of resistance r and a key as shown in the figure. When the switch ‘S’ is open, the null point is obtained at a distance of 51 cm from P. a) What do you mean by potential gradient? b) Determine the potential gradient across PQ. c) When the switch s is closed, will the null point move towards P or Q? Justify your answer. |
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| a) Find the equivalent resistance of the above circuit. b) Determine the current through the 75Ω resistance. |
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| Remya makes the a circuit as in figure to measure the emf of a cell. She says that the voltmeter reading will give the emf of the cell. a) The physics teacher says that it is not possible to measure the emf of the cell in this way. Justify this statement. b) Explain with a circuit diagram the method to measure the emf of a cell with a potentiometer if you are given another standard cell (whose e.m.f. is known). |
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The thermal velocity of electron is about 10 6 m/s and drift velocity is about 10 -3 m/s. a) What is meant by drift velocity? b) Obtain a relation between drift velocity and electric current. |
| The resistance ‘R’ of a conductor depends on its length ‘l’, area of cross section ‘A’ and the resistivity ‘ρ’ of the material. a) Write an expression connecting R, l, A and ρ. b) What happens to the resistivity of the material if the conductor is stretched to double its length? c) The voltage-current variation of two metallic wires ‘X’ and ‘Y’ at constant temperature are as shown in fig. Assuming that the wires have the same length and the same diameter, explain which of the wires will have larger resistivity. |
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| In the potentiometer circuit shown, the balance point is at X. State with reason, where the balance point will be shifted, when a) Resistance R is increased, keeping all parameters unchanged. b) Resistance S is increased, keeping R constant. c) Cell P is replaced by another cell whose e.m.f is lower than that of cell Q. d) You are asked to compare the e.m.f s of two cells using a potentiometer. Draw the circuit diagram for this and explain how you will determine the ratio of e.m.fs |
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| a) To construct an electric circuit, you want to select a 470 KΩ resistor with 5% tolerance. Draw a schematic diagram indicating the colour combinations that you will select. b) As the temperature of a metallic resistor is increased; the product of its resistivity and conductivity i) Increases ii) Decreases iii) Remains constant iv) May increases or decreases c) Draw a graph showing the relation between resistivity and temperature of a super conductor d) The circuit diagram of a potentiometer for the determination of internal resistance (r) of the cell Given R = 100Ω, balancing length when key (K) Open = 60 cm. Balancing length when key (K) closed = 50 cm. |
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| a) From the figures which curve corresponds to a typical semiconductor b) Dimension of temperature coefficient α is ............... c) Steady current flows in a metallic conductor of non-uniform cross-section. Which of the following quantities is a constant along the conductor? A) Current B) Current density C) Electric field D) Drift speed |
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Resistors are sometimes joined together and they have several applications in electronics a) Draw a series combination of three resistors R1 , R2 and R3 b) Obtain the expression for the effective resistance in the combination of two resistors R1 and R2 in parallel. Sketch the combination also c) Inspite of validity of Ohm’s law, it has some limitations. Give one limitation of Ohm’s law |
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(A) Potentiometer measures the potential difference more accurately than a voltmeter, because the potentiometer (a) does note draw current from the external circuit (b) has a wire of high resistance (c) draws a heavy current from the external circuit (d) has a wire of low resistance (B) With the help of a diagram explain the principle of a potentiometer (C) Using a potentiometer how do you determine the internal resistance of a cell? |
| Kirchhoff’s rules are very useful for the analysis of electrical circuits (A) State Kirchhoff’s junction rule (B) Find the effective resistance of the circuit given |
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(a) Which of the following obeys Ohms law? (i) Transistor (ii) Nichrome (iii) Diode (iv) Liquid electrolyte (b) A wire has a resistance of 10 Ω .It is stretched by 10 % of its original length, what will be the new resistance? (i) 10 Ω (ii) 11 Ω (iii) 9 Ω (iv)12.1 Ω (c) With the help of a circuit diagram describe the method to find the value of an unknown resistance using meter bridge arrangement |
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a) Which of the following material is used to make wire wound standard resistors? (i) Manganin (ii) Germanium (iii) Copper (iv) Carbon (b) A bread toaster and a bulb are connected parallel in a circuit. The toaster produces more heat than the bulb. Which of the following statement is true? (i) Resistance of toaster is greater than resistance of bulb (ii) Resistance of bulb same as the resistance of toaster (iii) Resistance of bulb is greater than resistance of toaster (iv) Cannot predict (c)With the help of a circuit diagram describe the method to find the internal resistance of a cell using potentiometer |
| (a) Resistivity of a conductor depends upon (i) its material (ii) its length (iii) its cross-sectional area (iv) All of the above (b) Calculate the current flowing through the following circuit (c) A potentiometer is a device to measure emf of a cell. Explain how the emfs of two cells can be compared using a potentiometer. |
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| How will you represent a resistance of 3700 + 5% using colour code ? |
| What do you mean by drift velocity? Write the relation between drift velocity and electric current. |
| A galvanometer is connected as shown in the figure (a) This combination can be used as ............... (voltmeter/rheostat/ammeter) (b) Derive an expression to tind the value of resistance S. |
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| The circuit diagram of a potentiometer for determining the emf E of a cell of negligible internal resistance is as shown in figure (a)State the principle of working of a potentiometer. (b)How the balancing length AJ changes when the value of R1 decreases? (c)Derive an expression to find out internal resistance of a cell. |
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| Write the unit of mobility. |
| The temperature dependence of resistivity of a material is shown below: (a) Identify the type of material. (b) Write the relation between resistivity and average collision time for electron |
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| The experimental set up to find an unknown resistance using a metre bridge is shown (a) What is the working principle of a metre bridge ? (b) If the balance point is found to be at 39.5 cm from the end A, the resistor S is of 12.5 Ω. Determine the resistance R. Why are the connections between resistors in a metre bridge made of thick copper strips ? (c) If the galvanometer and cell are interchanged at the balance point of the bridge, would the galvanometer show any current ? |
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| Three resistors R1 , R2 , R3 are to be combined as shown in the figures. (a) Identify the series and parallel combinations. (b) Which combination has lowest effective resistance ? (c) Arrive at the expression for the effective resistance of parallel combination. |
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| A Wheatstone bridge is shown in figure. (a) Derive a relation connecting the four resistors for the galvanometer to give zero or null deflection. (b) Name a practical device which uses this principle. |
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