MOST IMPORTANT QUESTIONS FOR CURRENT ELECTRICITY CBSE XII BY ATC
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This document contains a 30 question physics exam on topics related to current and electricity for Class XII. The exam covers concepts such as superconductors, current, resistance, Ohm's law, circuits, and applications of electricity. Questions involve calculations related to resistors, current, power, and electric cells. Diagrams and derivations of formulas are also assessed. The exam is designed based on the new CBSE board examination pattern for 2013-14.
MOST IMPORTANT QUESTIONS FOR CURRENT ELECTRICITY CBSE XII BY ATC
- 1. Guess Paper 2014 Class XII Subject - Physics (Based on the new pattern of CBSE board examination 2013-14) CURRENT & ELECTRICITY (NCERT unit 3) Time Allowed: 3 hours Maximum Marks: 70 Q.1> Give an example of a superconductor Q.2> What is current? Mention its SI unit. Q.3> Name 2 materials, which are used for making standard resistance coils. Q.4> What is the resistance corresponding to Red, Blue, Yellow and Silver? Q.5> Mention the colour coding for a 250-ohm resistor Q.6> How can a potentiometer be made more sensitive? Q.7> Why does the I-V graph of a conductor deviate from its straight line behavior at higher currents? Q.8> In a current carrying wire, 6 x 1023 electrons flow in 5 seconds. Find the current Q.9> When 2 resistors are joined in series, the net is 9 ohm. When these 2 resistors are joined in parallel the net is 2 ohm. Find the value of these resistors. Q.10> What are the possible values of resistances that can be obtained using 5ohm and 10ohm. Q.11> A set of n identical resistors each of resistance R, when connected in series give a net of X ohm and when connected in parallel give a net of Y ohm. Show that XY=R2 Q.12> Define electrical conductivity of a conductor and give its SI units Q.13> Define the term 'resistivity' and write its S.I. unit. Derive the expression for the resistivity of a conductor in terms of number density of free electrons and relaxation time. Q.14> A series combination of 2-ohm and 1-ohm resistors is connected across a battery of 6V and negligible internal resistance. The potential difference across the 2 ohm resistor is found using a (a) 30K-ohm voltmeter (b) 1K ohm voltmeter (c) Potentiometer If the readings obtained are V1, V2 and V3 then arrange them is ascending order. Q.15> Write a note on superconductivity explaining its cause and application. What is critical temperature. Q.16> State and derive ohms law. Q.17> A resistance has color coding as ( green,Red,brown,) and other one has (blue,black,grey). Find the ratio of power dissipated in first to the power dissipated in second if both are separately connected across 220V-power supply. Q.18> Using proper figure, explain why a voltmeter is connected in parallel but ammeter in series. Q.19> What is the cause of resistance. On what factors does it depend. Q.20> Three resistors 8立 , 4立 and 6立 are connected in parallel across a cell. The net current drawn from the cell is I1. When they are joined in series across the same cell the net current drawn is I2. Find the ratio I1 / I2 . Also determine the current through each resistance separately in both the cases. Q.21> A silver wire has a resistance of 2.0 ohms at 20oC and a resistance of 2.5 ohms at 100oC. Determine the temp coefficient of resistance. ------------------------------------------------------------------------------------------------------- www.anuragtyagiclasses.com | call us @ 09818777-622
- 2. Q.22> The maximum power rating of a 20-ohm resistor is 2.0KW ( That is, this is the maximum power the resistor can dissipate without melting ) Would you connect this resistor directly across a 300V DC supply. Explain. Can we connect two such resistors in series across the 300V supply? Q.23> In a meter bridge experiment, a fixed resistance of 10ohms is used. The balance length obtained while finding an unknown resistance is 40cm. Find the unknown resistance. Q.24> Give reasons a. The electron drift speed is estimated to be only a few mm/s . How can such a small speed account for instantaneous current b. Is a wire carrying current charged ? Why or why not Q.25> An electric bulb is marked as 100W at 200V. Find the power dissipated if instead of 200V supply the bulb is joined to a.> 400 volt supply b.> 2A constant current source Q.26> A wire of uniform cross section and length L has a resistance of 16ohm. It is cut into four equal parts. Each part is stretched uniformly to length L and all the four stretched parts are connected in parallel. Calculate the total resistance of the combination so formed. Q.27> A galvanometer has a coil resistance of 5-ohm and a current rating of 500mA. Explain how this can be converted into a (a) Voltmeter of range 10 volts (b) Ammeter of range 5A In each case, find the net resistance of the device Q.28> A house is fitted with 10 bulbs of 50W-200V each, 8 fans consuming 0.5 ampere at 200V each and an electric iron having a resistance of 250 ohms. If the power supplied is at 200Volts and the cost of energy is Rs. 5 per kWh. find the electricity bill for the month of June if all the above appliances are used for 5 hours in a day. Q.29> Deduce the condition for balance in a Wheatstone Bridge. Using the principle of Wheatstone Bridge, describe the method to determine the specific resistance of a wire in the laboratory. Draw the circuit diagram and write the formula used. Write any two important precautions that one should observe while performing the experiment Q.30> Cells of emf E and internal resistance r are connected in the form of a matrix with m rows each containg n cells connected in series. Derive an expression for the current that this combination will send across an external resistance R. What should be the value of R for this current to be maximum? (b) 12 cells, each of emf 1.5V and internal resistance 0.5 ohm , are arranged in m rows each containing n cells connected in series. Calculate the values of n and m for which this combination would send maximum current through an external resistance of R. OR Describe the formula for the equivalent EMF and internal resistance for the parallel combination of two cells with EMF E1 and E2 and internal resistances r1 and r2 respectively. What is the corresponding formula for the series combination? (b) Two cells of EMF 1V, 2V and internal resistances 2 and 1 respectively are connected in (i) series, (ii) parallel. What should be the external resistance in the circuit so that the current through the resistance be the same in the two cases? In which case more heat is generated in the cells ? ------------------------------------------------------------------------------------------------------- www.anuragtyagiclasses.com | call us @ 09818777-622