Chapter # 15 Electrical Measuring Instruments

PHYSICS

CHAPTER # 15 Electrical Measuring Instruments

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A moving coil d Arsenal galvanometer is based on the: a) Heating effect of current b) Magnetic effect of current c) Chemical effect of current d) Pettier effect of current A moving coil type of galvanometer is based upon the principle that: a) Wire carrying a current experiences a force in magnetic field b) Wire carrying current produces a magnetic field c) It has a horse shoe type magnet d) All are true In a moving coil galvanometer, we use a radial magnetic field so that the galvanometer scale is: a) Logarithmic b) Exponential c) Linear d) None of the above The coil of a sensitive moving coil galvanometer swings too far on both sides. This movement can quickly be stopped by: a) Connecting a large resistance across the ends of the coil b) Holding a magnet near the coil c) Connecting a short length of copper wire across the ends of the coil d) Earthing the case of the galvanometer The current that must flow through the coil of a galvanometer so as to produce a deflection of one division on its scale is called: a) Charge sensitivity of the galvanometer b) Current sensitivity of the galvanometer c) Micro-volt sensitivity d) None of the above The sensitivity of moving coil galvanometer depends on: a) The angle of deflection b) Earth’s magnetic field c) Torsion constant of the spring d) The moment of inertia of the coil The coil of a suspended coil galvanometer has very high resistance. When a momentary current is passed through the coil, it: a) Oscillates with the decreasing amplitude b) Oscillates with the same amplitude c) Gets deflected and comes to rest slowly d) Shoes steady deflection To measure the current in an electric device: a) Put an ammeter in parallel with it b) Put a voltmeter in parallel with it c) Put an ammeter in series with it d) Put a voltmeter in series with it The best instrument for the accurate measurement of the E.M.F. of a cell is: a) Voltmeter b) Ammeter c) Potentiometer d) Whetstone bridge A voltmeter always gives lower value of p.d. because: a) Some energy is lost in moving the needle b) Internal resistance of cell plays its role c) It absorbs some energy d) Both a) and b) true A galvanometer can be converted into a voltmeter by connecting: a) A high resistance in series b) A low resistance in parallel c) A low resistance in series d) A high resistance in parallel To convert a moving coil galvanometer into an ammeter one has to connect: a) A small resistance in series b) A small resistance in parallel c) A high resistance in series d) A high resistance in parallel Ohm meter is a device for directly measuring the resistance of conductor. It is a modification of: a) A moving coil galvanometer b) A voltmeter c) A rheostat d) All are true The whetstone bridge is most sensitive when: a) The ratio arm is equal to one b) The ratio arm is equal to ten c) Any value d) Both a) and b) are true Meter bridge is an application of: a) Whetstone bridge b) Potentiometer c) Neither a) nor b) d) Both a) and b) A potentiometer is an ideal instrument for measurement of p.d. or e.m.f. because: a) It has a long wire b) It uses a sensitive galvanometer c) It does not distribute the p.d. it measures d) Both a) and b) are true As for sensitiveness of a potentiometer: a) Five wires potentiometer is better than ten wires b) Ten wires potentiometer is better than four wires c) Both a) and b) have similar merits d) Both a) and b) is good

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CHAPTER # 15 Electrical Measuring Instruments

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Sensitivity of the potentiometer can be increased by: a) Increasing the e.m.f. of cell b) Increasing the length of the potentiometer wire c) Decreasing the length of the wire of potentiometer d) None of the above A potentiometer is superior to a voltmeter for measuring a potential because: a) The voltmeter has high resistance b) The resistance of the potentiometer wire is quite low c) The potentiometer does not draw any current from the unknown source of e.m.f. to be measured d) The sensitivity of potentiometer is higher than that of the voltmeter Potentiometer is an ideal instrument to measure potential difference because: a) At null point no current flows in the potentiometer wire b) At null point no current flows in the main circuit c) At null point no current flows in the secondary circuit d) None of the above A post office box has: a) Only two ratio arms fixed in it b) All the four ratio arms fixed in it c) Three ratio arms fixed in it d) Both a) and b) are true Post office box is an arrangement for finding resistance of a conductor and it makes use of: a) Whetstone bridge principle b) Potentiometer principle c) Fleming’s rule d) None of these A galvanometer of resistance 25 Ohm and having full scale deflection for a current of 10 mA is changes into voltmeter of range 100 volts by connecting a resistor R in series with the galvanometer. The resistance R in Ohm is: a) 10000 b) 110025 c) 975 d) 9975 A voltmeter with a resistance of 50  103 Ohm is used to measure voltage in a circuit. To increase its range to 3 times, the additional resistance to be put in series is: a) 105 ohm b) 150 k ohm c) 900 k ohm d) 9  106 ohm An induced e.m.f. is produced when a magnet is plunged into a coil. The strength of the induced e.m.f. is independent of: a) The strength of the magnet b) Number of turns of coil c) The resistivity of the wire of the coil d) Speed with which the magnet is moved A magnet is moved towards a coil (I) quickly (I) slowly, then the induced e.m.f. is: a) Larger in case (I) b) Smaller in case (I) c) Equal in both the cases d) Larger or smaller depending upon the radius of the coil Lenz’s law is consequence of the law of conservation of: a) Charge b) Mass c) Energy d) Momentum The law of electromagnetic induction have been used in the construction of a: a) Galvanometer b) Voltmeter c) Electric motor d) Generator A cylindrical bar magnet is kept along the axis of a circular coil. On rotating magnet about its axis, the coil which have induced in it: a) A current b) No current c) Only an e.m.f. d) Both an e.m.f. and a current When a magnet with its magnetic movement along the axis of a circular coil and directed towards the coil is withdrawn away from the coil, parallel to itself, the current in the coil, as seen by the withdrawing magnet is: a) Zero b) Clockwise c) Anti-clock wise d) None A coil of insulated wire is connected to a battery. If it is taken to galvanometer, its pointer is deflected, because: a) Induced current is produced b) The coil acts like a magnet c) The number of turns in the coil of the galvanometer are changed d) None of the above

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CHAPTER # 15 Electrical Measuring Instruments

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When the rate of change of current is unity, the induced e.m.f. is equal to: a) Total flux lined with the coil b) Coefficient of self-induction c) Number of self-induction d) Thickness of the coil 37. When current i passed through an inductor of self inductance L, energy stored in it is 1/2 L i 2. This is stored in the: a) Current b) Voltage c) Magnetic field d) Electric field 38. A dynamo: a) Creates electrical energy b) Converts mechanical energy into electrical energy c) Converts electrical energy into mechanical energy d) Creates mechanical energy 39. A transformer: a) Transforms energy b) Transforms frequency c) Transforms voltage d) Generates e.m.f. 40. Transformer works on: a) a.c. only b) d.c. only c) high voltage only d) a.c. and d.c. both 41. In a step-up transformer, the number of turns in: a) Primary are less b) Primary are more c) Primary and secondary are equal d) Primary are infinite  42. Flux (in weber) in a closed circuit of resistance 10 varies with time t (in second) according to the  2 equation: = 6t – 5t + 1

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What is the magnitude of the induced current a) 1.2 Amp b) 0.8 Amp c) 0.6 Amp d) 0.2 Amp Alternating current is one which changes in: a) Directions b) Magnitudes c) Magnitudes as well as direction d) None of the above Alternate voltage is: a) Independent of time b) Varies inversely as time c) Varies directly with time d) Varies sinusoidal with time Once complete set of positive and negative values of alternating quantities is called: a) Time period b) Frequency c) Amplitude d) Cycle The frequency of A.C Mains in Pakistan is: a) 30 c/s b) 50 c/s c) 60 c/s d) 120 c/s A.C can be measured with the help of: a) Moving coil galvanometer b) Hot wire ammeter c) Tangent galvanometer d) Hot wire voltmeter Hot wire ammeters are used for measuring: a) A.C. only b) D.C. only c) Both A.C. and D.C d) None of the above Alternating current cannot be measured by D.C. ammeter because: a) A.C. cannot pass through D.C. ammeter b) Average value of current for complete cycle is zero c) A.C is virtual d) A.C changes its direction Alternating current/e.m.f measuring instrument measure its: a) r.m.s value b) speak value c) average value d) square of current and voltage Alternating current is converted to direct current by: a) Rectifier b) Dynamo c) Transformer d) Motor A transformer is employed to: a) Convert A.C. into D.C b) Convert D.C into A.C c) Obtain a suitable A.C voltage d) Obtain a suitable D.C voltage A capacitor is perfectly insulator for: a) Direct current b) Alternating current c) Direct as well as alternating current d) None of the above

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CHAPTER # 15 Electrical Measuring Instruments

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Galvanometer is used to measure: a) Large current (A) b) Small current (mA,  A) c) Voltage (V) d) None of these Ammeter is used to measure: a) Large current (A) b) Small current (mA,  A) c) Large Voltage d) Small Voltage A voltmeter measure the voltage of a source of P.D across a circuit, when is connected: a) In series with the battery of circuit b) In parallel with the battery of circuit c) In series of parallel with battery or circuit d) All of the above ways A galvanometer can be converted into a voltmeter by connecting a suitable: a) Low resistance in series with its coil b) Low resistance in parallel with its coil c) High resistance in series with its coil d) High resistance in parallel with its coil Electrical measuring instruments are devices, which convert: a) Heat energy into electrical energy b) Chemical energy into electrical energy c) Electrical energy into mechanical energy d) None of the above Galvanometer has: a) Variable resistance b) Fixed resistance c) both a) & b) d) None of the above An ammeter is used to measure: a) Current b) Voltage c) Resistance in the circuit d) None of these The shunt resistance is used with galvanometer to limit the current as: a) In series combination with galvanometer b) In parallel combination with galvanometer c) Both a) & b) d) None of these When current flows in a rectangular coil placed in a magnetic field experiences: a) Magnetic torque b) Electromagnetic torque c) Does not experience any effect d) None of the above The working of all electrical instruments depend upon: a) Magnetic effect of current b) Chemical effect of current c) Electromagnetic effect of current d) None of the above The current passing through coil of galvanometer is: a) Directly proportional to the angle of deflection b) Inversely proportional to angle of deflection c) None of the above d) Both of these A galvanometer is used: a) To measure voltage across a circuit b) To measure the current through the circuit c) To measure the resistance of the circuit d) None of the above Which of the following is used to measure current, voltage and resistance: a) Ammeter b) Voltmeter c) Avometer d) Galvanometer The sensitivity of moving coil galvanometer can be increased by: a) Decreasing area of coils b) Decreasing the No. turns of coil c) Increasing the magnetic field d) None of the above Voltmeter is used to measure the: a) Current b) Resistance c) Temperature d) Voltage In order to increase the range of an Ammeter, the shunt resistance is: a) Increased b) Decreased c) Kept constant d) None of the above A galvanometer can be converted into ammeter by connecting: a) High resistance in series b) High resistance in parallel c) Low resistance in series d) Low resistance in parallel with gal’ometer Wheat stone bridge is an arrangement consisting of: a) Three resistance b) Four resistance c) Two resistance d) None of these A balanced wheat stone bridge is used to determine: a) Current b) Potential difference across a resistance c) An unknown resistance d) Very high resistance

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When the wheat stone bridge is balanced then: a) Maximum current flows through the galvanometer b) Potential difference across galvanometer is zero c) Potential difference across galvanometer is maximum d) None of the above Which of the following instrument can measure the unknown resistance with sufficient accuracy: a) Potentio meter b) Slide Wire Bridge c) Galvanometer d) Post office Box Post office box is a practical form of: a) Potentio-meter b) Ohmmeter c) Wheat stone bridge d) None of the above Potentio meter can be used as: a) Ammeter b) Volt meter c) Galvanometer d) Potential divider A balanced wheat stone bridge is used to determine: a) An unknown resistance b) The current through a resistance c) The potential difference across a resistance d) The current through galvanometer The construction of a post office box is based on the principle of: a) Ammeter b) Voltmeter c) Galvanometer d) Wheat stone bridge A post office box is used to measure: a) Current flowing in a circuit b) Voltage across the terminals of a battery c) P.D between two points of a circuit d) Unknown resistance The construction of a slide wire bridge is based on the principle of a: a) Galvanometer b) Generator c) Voltmeter d) Wheat Stone Bridge A potentio meter is used to measure: a) Current b) Voltage c) Unknown resistance d) Internal resistance of a cell A potentio meter is a most accurate potential measuring device because: a) It has low resistance as compared to a voltmeter b) In it the potential difference is directly proportional to the length of the wire c) A uniform and long wire is used in it d) It does not draw any current from the circuit A galvanometer is connected in a slide wire bridge or potentio meter: a) To detect the current flowing through the circuit b) To measure the potential difference c) Because its resistance is very small d) Because its balance point is located when its deflection is zero An AVO meter is used to measure: a) Current b) Resistance c) Voltage d) All of the above

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