CURRENT ELECTRICITY MULTIPLE CHOICE QUESTIONS

1. In the following figure potential difference between A and B is . 0 volt 10 volt 5 volt 15 volt

2. The lead wires should have Larger diameter and low resistance Smaller diameter and low resistance Smaller diameter and high resistance Larger diameter and high resistance

3. What is unit for specific resistance ?. [Rugved] ohm/cm ohm.cm.cm ohm.cm ohm

4. A metal wire of specific resistance 64 x 10-6 Ωcm and length 198 em has resistance of 7 Ω. The radius of the wire will be 2.4 cm 0.024 cm 0.24 cm 24 cm

5. A wire of 50 cm long and 1 mm² in cross-sectional area carries a current 4A when connected to a 2V battery. The resistivity of the wire is 2 x 10 -7 Ωm 4 x 10 -6 Ωm 5 x 10 -7 Ωm 1 x 10 -6 Ωm 6. The current from the battery in circuit diagram shown is . 1 A 1.5 A 2 A 3 A 7. If an ammeter is to be used in place of a voltmeter the we must connect with the ammeter a Low resistance in parallel High resistance in series High resistance in parallel Low resistance in series 8. An unknown resistance R1 is connected in series with a resistance of 10Ω. This combination is connected to one gap of a metre bridge while a resistance R2 is connected in the other gap. The balance point is at 50 em. Now, when the 10 Ω resistance is removed the balance position shifts to 40 em. The value of R1 is (in ohm) 10 40 20 60 9. If six identical cells each having an emf of 6 V are connected in parallel, the emf of the combination is 1V 1/6 V 36V 6V 10. Two wires of the same dimensions but resistivities P1 and P2 are connected in series. The equivalent resistivity of the combination is ρ₁ + ρ₂ √ρ₁ρ₂ ρ₁ + ρ₂ / 2 2(ρ₁ + ρ₂) 11. Identify the set in which all the three materials are good conductor of electricity Cu, Ag, Au Cu, Hg, NaCI Cu, Si, Diamond Cu, Ge, Hg 12. At what temperature will the resistance of a copper wire become three times its value at 0°C? (Temperature coefficient of resistance for copper = 4 x 10-3 per 0C) 400 0 c 500 0 c 450 0 c 550 0 c 13. Two wires of the same material are given. The first wire is twice as long as the second and has twice the diameter of the second. The resistance of the first will be Twice of the second Equal to the second Half of the second Four times of the second 14. Potential difference between the points P and Q in the electric circuit shown is. 4.5 V 2.4 V 1.1 V 2.88 V 15. In a metre bridge experiment null point is obtained at 20 em. from one end of the wire when resistance X is balanced against another resistance Y. If X < Y, then where will be the new position of the null point from the same end, if one decides to balance a resistance of 4 X against Y 40 cm 50 cm 80 cm 70 cm 16. There are three voltmeters of the same range but of resistances 10000 Ω, 8000 Ω and 4000 Ω respectively. The best voltmeter among these is the one whose resistance is 10000 Ω 40000 Ω 80000 Ω None of these 17. If in the circuit shown, the internal resistance of the battery is 1.5 Ω and VP and VQ are the potentials at P & Q respectively what is the potential difference between P and Q . Zero 4 volts (VQ > VP) 4 volts (VP > VQ) 2.5 volts (VQ > VP) 18. In a typical Wheatstone network the resistances in cyclic order are A = 10 Ω, B = 10 Ω, C = 4 nand D = 4 Ω. For the bridge to be balanced. 10 Ω should be connected in parallel with A 5 Ω should be connected in series with B 10 Ω should be connected in series with A 5 Ω should be connected in parallel with B 19. The resistance of 20 em long wire is 5 ohm. The wir~ is stretched to a uniform wire of 40 em length. The resistance now will be (in ohms) 5 20 10 200 20. If a wire of resistance R is melted and recasted to half of its length, then the new resistance of the wire will be. [KCET (Med.) 200] R/4 R R/2 2R 21. A cell of internal resistance 3 ohm and emf 1 volt is connected to a uniform wire of length 500 em and resistance 3 ohm. The potential gradient in the wire is 30 mV/cm 20 mV/cm 1 mV/cm 4 mV/cm 22. Four resistances are connected in a circuit in the given figure. The electric current flowing through 4 ohm a 6 ohm resistance is respectively . 2 amp and 4 amp 1 amp and 1 amp 1 amp and 2 amp 2 amp and 2 amp 23. The resistance of a conductor is 5 ohm at 50°C and 6 ohm at 100°C. Its resistance at 0°C is 1 ohm 3 ohm 2 ohm 4 ohm 24. The potential difference between points A and B of adjoining figure is . 2/3 V 4/3 V 8/9 V 2 V 25. Two wires A and B of same material and same mass have radius 2 r and r. If resistance of wire A is 34 Ω, then resistance of B will be 544 Ω 68 Ω 272 Ω 17 Ω 26. Which of the following does not obey Ohm's law Copper Diode-valve Aluminium None of these 27. The equivalent resistance of the following diagram between A and B is. 2/4 Ω 6 Ω 9 Ω none of these 28. The resistors of resistances 2 Ω, 4 Ω and 8 Ω are connected in parallel, then the equivalent resistance of the combination will be 8/7 Ω 7/4 Ω 7/8 Ω 4/9 Ω 29. By increasing the temperature, the specific resistance of a conductor and semiconductor Increases for both Increases, decreases Decreases for both Decreases for both 30. The resistivity of a wire depends on its Length Shape Area of cross-section Material 31. Read the following statements carefully Y: The resistivity of a semiconductor decreases with increase of temperature Z : In a conducting solid, rate of collisions between free electrons and ions increases with increases of temperature Select the correct statements (s) from the following Y is true but Z is false Both Y and Z are true Y is false but Z is tru 32. A uniform wire of resistance R is uniformly compressed along its length, until its radius becomes n times the original radius. New resistance of the wire becomes R/n⁴ R/n R/n² nR 33. The internal resistance of a cell is the resistance of Electrodes of the cell Electrolyte used in the cell Vessel of the cell Material used in the cell 34. A wire of resistance 10 Ω is bent to form a circle,Pand Q are points on the circumference of the circle dividing it into a quadrant and are connected to a battery of 3 V and internal resistance 1 Ω as shown in the figure. The currents in the two parts of the circle are . 6/23 A and 18/23 A 4/25 A and 12/25 A 5/26 A and 15/26 A 3/25 A and 9/25 A 35. Two resistance wires on joining in parallel, the resultant resistance is 6/5 Ω. One of the wire breaks. The effective resistance is 2 Ω. The resistance of the brokes wire was 3/5 Ω 6/5 Ω 2 Ω 3 Ω 36. Six identical cells of emf E and internal resistance r are connected in parallel, then the net emf and internal resistance of the combination will be 6E: 6r E,6r E,r/6 E/6,r/6 37. The resistance of a wire is R. If the length of the wire is doubled by stretching, then the new resistance will be 2R R 4R R/4 38. Resistances of 6 ohm each are connected in the manner shown in adjoining figure. With the current ampere as shown in figure, the potential difference VP - VQ is . 3.6 V 3.0 v 6.0 v 7.2 v 39. Two resistance r1 and r2 (r1 < r2 ) are connected in parallel. Their equivalent resistance R is R < r1 r1 < R < ( r1 + r2) r1 < R < r2 R < ( r1 > r2) 40. An ammeter reads upto 1 ampere. Its internal resistance is 0.81 ohm. To increase the range to 10 A the value of the required shunt is 0.09 Ω 0.3 Ω 0.03 Ω 0.9 Ω 41. In the given figure, when galvanometer shows no deflection, the current (in ampere) flowing through 5Ω resistance will be. 0.5 0.9 0.6 1.5 42. When cells are arranged in parallel The current capacity decreases The emf increases The current capacity increases The emf decreases 43. A uniform wire of resistance 9 n is cut into 3 equal parts. They are connected in the form of equilateral triangle ABC. A cell of emf 2V anj negligible internal resistance is connected across B and C. Potential difference across AB is 1 V 3V 2V 0.5V 44. The internal resistance of a cell of emf 12 V is 5 x 10 -2 Ω . It is connected across an unknown resistance. Voltage across the cell, when a current of 60 A is drawn from it, is 15 V 9 V 12 V 6 V 45. Two cells each of emf E and internal resistance r are connected parallel across a resistor R. The power dissipated in the resistor is maximum if R = r R = 3r/2 R = 2r R = r/2 46. If the current through 3 n resistor is 0.8 A then the potential drop through 4 Ω resistor is. 9.6 V 2.6 V 4.8 V 2.2 V 47. Three resistors are connected to form the sides of a triangle ABC, the resistance of the sides AB, BC and CA are 40 ohms; 60 ohms and 100 ohms respectively. The effective resistance between the points A and B in ohms will be. [JIPMER 2002] 32 50 64 200 48. The resistance of a coil is 4.2 Ω at 100°C and the temperature coefficient of resistance of its material is 0.004 °C. Its resistance at Q °C is 6.5 C 3Ω 5Ω 4Ω 49. The resistance of an incandescent lamp is Greater when switched off The same whether it is switched off or switched on Smaller when switched on None of these 50. The number of dry cells, each of emf 1.5 volt and internal resistance 0.5 ohm that must be joined in series with a resistance of 20 ohm so as to send a current of 0.6 ampere through the circuit is 2 10 8 12

COMMUNICATIONS GRADE 12 MCQ QUESTIONS

1. Indicate which one of the following system is digital Pulse position modulation Pulse width modulation Pulse code modulation Pulse amplitude modulation 2. Basically, the product modulator is An amplifier A frequency separator A mixer A phase separator 3. The maximum distance upto which TV transmission from a TV tower of height h can be received is proportional to . [AIIMS 2003] h1/2 h3/2 h h2 4. Advantage of optical fibre . [DCE 2005] High bandwidth and EM interference High band width, low transmission capacity and no EM interference Low bandwidth and EM interference High bandwidth, high data transmission capacity and no EM interference 5. Laser beams are used to measure long distances because . [DCE 2002, 03] They are monochromatic They are coherent They are highly polarised They have high degree of parallelism 6. Range of frequencies allotted for commercial FM radio broadcast is . [MNR 1997] 88 to 108 MHz 8 to 88 MHz 88 to 108 kHz 88 to 108 GHz 7. The phenomenon by which light travels in an optical fibres is . [DCE 2001] Reflection Total internal reflection Refraction Transmission 8. Consider telecommunication through optical fibres. Which of the following statements is not true . [AIEEE 2003] Optical fibres may have homogeneous core with a suitable cladding Optical fibres are subject to electromagnetic interference from outside Optical fibres can be of graded refractive index Optical fibres have extremely low transmission loss 9. In which of the following remote sensing technique is not used . [Kerala PMT 2005] Forest density Wetland mapping Pollution Medical treatment 10. What is the modulation index of an over modulated wave 1 < 1 Zero > 1 11. An antenna is a device That converts electromagnetic energy into radio frequency signal That converts guided electromagnetic waves into free space electromagnetic waves and vice-versa That converts radio frequency signal into electromagnetic energy None of these 12. Which of the following is the disadvantage of FM over AM Larger band width requirement Higher modulation power Larger noise Low efficiency 13. For sky wave propagation of a 10 MHz signal, what should be the minimum electron density in ionosphere .[AIIMS 2005] ~ 1.2 * 10¹² per m³ ~ 10¹⁴ per m³ ~ 10⁶ per m³ ~ 10²² per m³ 14. The process of superimposing signal frequency (i.e. audio wave) on the carrier wave is known as . [AIIMS 1987] Transmission Modulation Reception Detection 15. In an amplitude modulated wave for audio frequency of 500 cycle/second, the appropriate carrier frequency will be . [AMU 1996] 50 cycles/sec 500 cycles/sec 100 cycles/sec 50,000 cycles/sec 16. In short wave communication waves of which of the following frequencies will be reflected back by the ionospheric layer, having electron density 1011 per m3 . [AIIMS 2003] 2 MHz 12 MHz 10 MHz 18 MHz 17. For television broadcasting, the frequency employed is normally . [AMU 2002] 30-300 MHz 30-300 KHz 30-300 GHz 30-300 Hz 18. Through which mode of propagation, the radio waves can be sent from one place to another . [JIPMER 2003] Ground wave propagation Space wave propagation Sky wave propagation All of them 19. A laser beam is used for carrying out surgery because it . [AIIMS 2003] Is highly monochromatic Is highly directional Is highly coherent Can be sharply focussed 20. The waves used in telecommunication are IR Microwave UV Cosmic rays 21. Audio signal cannot be transmitted because . [Kerala PMT 2005] The signal has more noise The transmitting antenna length is very small to design The signal cannot be amplified for distance communication The transmitting antenna length is very large and impracticable 22. A step index fibre has a relative refractive index of 0.88%. What is the critical angle at the corecladding interface . [Manipal 2003] 60° 45° 75° None of these 23. Television signals on earth cannot be received at distances greater than 100 km from the transmission station. The reason behind this is that . [DCE 1995] The receiver antenna is unable to detect the signal at a distance greater than 100 km The TV signals are less powerful than radio signals The TV programme consists of both audio and video signals The surface of earth is curved like a sphere 24. In frequency modulation . [Kerala PMT 2005] The amplitude of modulated wave varies as frequency of carrier wave The amplitude of modulated wave varies as amplitude of carrier wave The frequency of modulated wave varies as amplitude of modulating wave The frequency of modulated wave varies as frequency of modulating wave 25. In an FM system a 7 kHz signal modulates 108 MHz carrier so that frequency deviation is 50 kHz. The carrier swing is 7.143 0.71 8 350