Latest Objective Questions On Electric Current and Ohm’s Law
1.Resistivity of a wire depends on
(C) cross section area
(D) none of the above.
2. When n resistances each of value r are connected in parallel, then resultant resistance is x. When these n resistances are connected in series, total resistance is
(C) x / n
(D) n2 x.
3. Resistance of a wire is r ohms. The wire is stretched to double its length, then its resistance in ohms is
(A) r / 2
(B) 4 r
(C) 2 r
(D) r / 4.
4. Kirchhoff’s second law is based on law of conservation of
5. The diameter of the nucleus of an atom is of the order of
(A) 10 -31 m
(B) 10 -25 m
(C) 10 -21 m
(D) 10 -14m.
6. The mass of proton is roughly how many times the mass of an electron?
7. The charge on an electron is known to be 1.6 x 10-19 coulomb. In a circuit the current flowing is 1 A. How many electrons will be flowing through the circuit in a second?
(A) 1.6 x 1019
(B) 1.6 x 10-19
(C) 0.625 x 1019
(D) 0.625 x 1012.
8. Two bulbs marked 200 watt-250 volts and 100 watt-250 volts are joined in series to 250 volts supply. Power consumed in circuit is
(A) 33 watt
(B) 67 watt
(C) 100 watt
(D) 300 watt.
9. Ampere second could be the unit of
10. Which of the following is not the same as watt?
(C) amperes x volts
(D) ( amperes )2 x ohm.
11. One kilowatt hour of electrical energy is the same as
(A) 36 x 105 watts
(B) 36 x 10s ergs
(C) 36 x 105 joules
(D) 36 x 105 B.T.U.
12. An electric current of 5 A is same as
(A) 5 J / C
(B) 5 V / C
(C) 5 C / sec
(D) 5 w / sec.
13. An electron of mass m kg and having a charge of e coulombs travels from rest through a potential difference of V volts. Its kinetic energy will be (A) eV Joules
(B) meV Joules
(C)me / V Joules
(D)V / me Joules.
14. The value of the following is given by 100 (kilo ampere ) x ( micro ampere ) 100 milli ampere * 10 ampere
(A) 0.001 A
(B) 0.1 A
(C) 1 A
15. A circuit contains two un-equal resistances in parallel
(A) current is same in both
(B) large current flows in larger resistor
(C) potential difference across each is same
(D) smaller resistance has smaller conductance.
16.Conductance is expressed in terms of
(A) ohm / m
(B) m / ohm
(C) mho / m
17. Which of the following could be the value of resistivity of copper?
(A) 1.7 x 10-8 ohm-cm
(B). 1.7 x 10-6 ohm-cm
(C). 1.6 x 10-5 ohm-cm
(D). 1.7 x 10-4 ohm-cm
18. A copper wire of length l and diameter d has potential difference V applied at its two ends. The drift velocity is vd. If the diameter of wire is made d/3, then drift velocity becomes
(A) 9 vd
(B) vd / 9
19.Two resistances R1 and R2 give combined resistance of 4.5 ohms when in series and 1 ohm when in parallel. The resistances are
(A)3 ohms and 6 ohms
(B)3 ohms and 9 ohms
(C)1.5 ohms and 3 ohms
(D)1.5 ohms and 0.5 ohms.
20. We have three resistances of values 2 Ω, 3 Ω and 6 Ω. Which of the following combination will give an effective resistance of 4 Ω?
(A) All the three resistances in parallel
(B) 2 Ω resistance in series with parallel combination of 3 Ω and 6 Ω resistance
(C) 3 Ω resistance in series with parallel combination of 2 Ω and 6 Ω resistance
(D) 6 Ω resistance in series with parallel combination of 2 Ω and 3 Ω resistance.
21. Three equal resistors connected in series across a source of emf together dissipate 10 watts of power. What would be the power dissipated in the same resistors when they are connected in parallel across the same source of emf?
(A) 10 watts
(B) 30 watts
(C) 90 watts
(D) 270 watts.
22.Current I in the figure is
23.Four identical resistors are first connected in parallel and then in series. The resultant resistance of the first combination to the second will be
(A) 1 / 16 times
(B) 1 / 4 times
(C) 4 times
(D) 16 times.
24.Twelve wires of same length and same cross-section are connected in the form of a cube as shown in figure below. If the resistance of each wire is R, then the effective resistance between P and Q will be
(B) 5 / 6 R
(C) 3 / 4 R
(D) 4 / 3 R.
25. When P = Power, V = Voltage, I = Current, R = Resistance and G = Conductance, which of the following relation is incorrect?
(A) V = √ (PR)
(B). P= V2G
(C) G= P / I2
(D) I =√ (P / R)
26.The unit of electrical conductivity is
(A) mho / metre
(B) mho / sq. m
(C) ohm / metre
(D) ohm / sq. m.
27.Which of the following bulbs will have the least resistance ?
(A) 220 V, 60 W
(B) 220 V, 100 W
(C) 115 V, 60 W
(D) 115 V, 100 W.
28.The ratio of the resistance of a 100 W, 220 V lamp to that of a 100 W, 110 V lamp will be nearly
(C) 1 / 2
(D) 1 / 4
29.The resistance of a 100 W, 200 V lamp is
(A) 100 ohm
(B) 200 ohm
(C) 400 ohm
(D) 1600 ohm.
30.Two 1 kilo ohm, 1/2 W resistors are connected in series. Their combined resistance value and wattage will be
(A) 2 kΩ, 1/2 W
(B) 2 kΩ, 1 W
(C) 2 kΩ, 2 W
(D) l kΩ, 1/2 W.
31.Which method can be used for absolute measurement of resistances ?
(A)Ohm’s law method
(B)Wheatstone bridge method
(D) Lortentz method.
32.Three 3 ohm resistors are connected to form a triangle. What is the resistance between any two of the corners?
(A) 3 / 4 ohms
(B) 3 ohms
(C) 2 ohms
(D) 4/3 ohm.
33.Five resistances are connected as shown in figure below. The equivalent resistance between the points A and B will be
(A) 35 ohms
(B) 25 ohms
(C) 15 ohms
(D) 5 ohms.
34.How many different combinations may be obtained with three resistors, each having the resistance R ?
35.A wire of 0.14 mm diameter and specific resistance 9.6 micro ohm-cm is 440 cm long. The resistance of the wire will be
(A) 9.6 ohm
(B) 11.3 ohm
(C) 13.7 ohm
(D) 27.4 ohm.
36.Ohm’s law is not applicable to
(A) DC circuits
(B) high currents
(C) small resistors
37.A metal resistor has resistance of 10 ohm at 0°C and 11 ohms at 160°C, the temperature coefficient is
(A) 0.00625 / °C
(B) 0.0625 /°C
(C) 0.000625 /°C
(D) 0.625 /°C.
Five resistances are connected as shown and the combination is connected to a 40 V supply.
38. Voltage between point P and Q will be
(A) 40 V
(B) 22.5 V
(C) 20 V
(D) 17.5 V.
39.The current in 4 ohm resistor will be
(A) 2.1 A
(B) 2.7 A
(C) 3.0 A
(D) 3.5 A.
40.Least current will flow through
(A) 25 ohm resistor
(B) 18 ohm resistor
(C) 10 ohm resistor
(D) 5 ohm resistor.
41.Total power loss in the circuit is
(B) 50.2 W
(C) 205 W
(D) 410 W.
42.A resistance of 5 ohms is further drawn so that its length becomes double. Its resistance will now be
(A) 5 ohms
(B) 7.5 ohms
(C) 10 ohms
(D) 20 ohms.
43.Specific resistance of a substance is measured in
44.A wire of resistance R has it length and cross-section both doubled. Its resistance will become
(A) 4 R
(D) R / 4.
45.Ohm’s law is not applicable in all the following cases Except
(B) Arc lamps
(A) Vacuum ratio values.
46.The element of electric heater is made of
47. 5xl016 electrons pass across the section of a conductor in 1 minute 20 sec. The current flowing is
(B) 0.1 mA
(D) 10 mA.
48.Which of the following figures represents the effect of temperature on resistance for copper ?
(A) figure A
(B) figure B
(C) figure C
(D) figure D.
49.Three elements having conductance G1, G2 and G3 are connected in parallel. Their combined conductance will be
(A) 1/( 1/G1 + 1/G2 + 1/G3)
(B) (G1G2 + G2G3 + G3G1)/(G1 + G2 + G3)
(C) 1/(G1 + G2+ G3)
(D) G1 + G2 +G3
50.The variation of resistance of iron and some alloys with temperature is shown in figure. The variation of carbon will be represented by
(A) curve A
(B) curve B
(C) curve C
(D) curve D.
51.Curves A and B represent the properties for materials which have
(A) low resistance
(B) low conductance
(C) negative resistance
(D) negative temperature coefficient.
52.Which of the following has negative temperature coefficient ?
53.All of the following have negative temperature coefficient EXCEPT
54.For the circuit shown below the current I flowing through the circuit will be
(A)1 / 2 A
(B) 1 A
(C) 2 A
(D) 4 A.
55.A cube of material of side 1 cm has a resistance of 0.002 ohm between its opposite faces. If the same volume of the material has a length of 8 cm and a uniform cross-section, the resistance of this length will be
(A) 0.032 ohm
(B) 0.064 ohm
(C) 0.096 ohm
(D) 0.128 ohm.
56.A standard 60 W bulb is in series with a room heater and connected across the mains. If the 60 W bulb is replaced by 100 W bulb
(A) the heater output will increase
(B) the heater output will reduce
(C) the heater output will remains unaltered.
57. Two aluminium conductors have equal length. The cross-sectional area of one conductor is four times that of the other. If the conductor having smaller cross-sectional area has a resistance of 100 ohms the resistance of other conductor will be
(A) 400 ohms
(B) 100 ohms
(C) 50 ohms
(D) 25 ohms.
58.A nichrome wire used as heater coil has the resistance of 1 ohm/m. For a heater of 1000 W at 200 V, the length of wire required will be
(A) 10 m
(B) 20 m
(C) 40 m
(D) 80 m.
59.The hot resistance of a tungsten lamp is about 10 times the cold resistance. Accordingly, cold resistance of a 100 W, 200 V lamp will be
(A) 4000 ohm
60. Variable resistors are
(A)Wire wound resistors
(B)Thin film resistors
(C)Thick film resistors
(D)All of the above.
61.Low resistance can be accurately measured by
(A) Kelvin bridge
(B )Wheat stone bridge
(C) Wein’s bridge
(D) None of the above.
62.A heating element of a hot plate on an electric cooking range draws 12 amperes from 240 V mains. How many kWh of energy will be consumed in one hour and 15 minutes
63. Temperature coefficient of resistance is expressed in terms of
(A) ohms / ohms oC
(B) mhos / ohm oC
(C) mhos / oC
(D) ohms / oC.
64. If R1 is the resistance of a coil of copper at t oC and RT is the resistance at T oC and also the resistance temperature coefficient of copper per degree centrigrade at 0oC is 1/234.45, then Rt/RT
(A) (1+t) / (1+T)
(B) (1+ 234.45t) / (1+234.45 T)
(C) (234.45 + t) / (234.45 + T)
(D) (234.45 + t2 ) / (234.45 + T 2).
65. Resistivity is usually expressed in terms of
(B) ohm / oC
66. Which material is expected to have least resistivity?
67. The shunt winding of a motor has a resistance of 85 ohm at 22oC. When the motor runs at full load, its resistance increases to 100 ohms. The resistance temperature coefficient of winding per 0oC is 0.004. The rise in temperature of the winding will be nearly
68. The resistance temperature coefficient is defined as
(A) increase in resistance per degree centigrade
(B) decrease in resistance per degree centigrade
(C) the ratio of increase in resistance per degree centigrade to the resistance at 0oC
(D) the ratio of increases in resistance per degree centigrade to the rate of rise of resistance at 0oC.
69.Two coils connected in series have resistance of 600 ohm and 300 ohm and temperature coefficients of 0.1% and 0.4% respectively.The resistance of the combination at 50oC will be
(A) 1050 ohm
(D) 990 ohm.
70. A 100 W, 200 V filament lamp has operating temperature of 2000oC. The filament material has resistance temperature coefficient of 0.005 at 0oC per oC. The current taken by the lamp at the instant of switching with 200 V supply with filament temperature of 20oC will be
(A) 1 A
(B) 3 A
(C) 5 A
71. A fuse is always installed in a circuit is
72. The rating of fuse wire is expressed in terms of
73. Which of the following material is not used as fuse material?
74. The voltage drop across the resistor 9 ohm will be
(B) 12 V
(C) 9 V
(D) 6 V.
75. The voltage drop will be least in which resistor ?
(A) 2 ohm
(B) 3 ohm
(C) 6 ohm
(D) 3 ohm and 6 ohm.