JEE Questions for Physics Current Electricity I Quiz 7 - MCQExams.com

A metallic block has no potential difference applied across it, then the mean velocity of free electrons is (T = absolute temperature of the block)
  • Proportional to T
  • Proportional to √T
  • Zero
  • Finite but independent of temperature
The drift velocity of the electrons in a copper wire of length 2 m under the application of a potential difference of 200 V is 0.5 ms–1. Their mobility is(in m2V–1s–1)
  • 2.5 × 10–3
  • 2.5 × 10–2
  • 5 × 102
  • 5 ×10–3
The resistance of a metal increases withincreasing temperature because
  • The collisions of the conducting electrons with the electrons increase
  • The collisions of the conducting electrons with the lattice consisting of the ions of the metal increase
  • The number of conduction electrons decreases
  • The number of conduction electrons increases
In the absence of applied potential, the electric current flowing through a metallic wire is zero because
  • The electrons remain stationary
  • The electrons are drifted in random direction with a speed of the order of 10–2cm/s
  • The electrons move in random direction with a speed of the order close to that of velocity of light
  • Electrons and ions move in opposite direction
Dimensions of a block are 1 cm × 1 cm × 100 cm. If specific resistance of its material is 3 × 10–7ohm-m, then the resistance between the opposite rectangular faces is
  • 3 × 10–9Ω
  • 3 × 10–7Ω
  • 3 × 10–5Ω
  • 3 × 10–3Ω
In the above question, the resistance between the square faces is
  • 3 × 10–9Ω
  • 3 × 10–7Ω
  • 3 × 10–5Ω
  • 3 × 10–3Ω
When an electrical appliance is switched on, it responds almost immediately, because
  • The electrons in the connecting wires move with the speed of light
  • The electrical signal iscarried by electromagnetic waves moving with the speed of light
  • The electrons move with speed which is close to but less than speed of light
  • The electron are stagnant
The resistance of a wire of uniform diameter d and length L is R. The resistance of another wire of the same material but diameter 2d and length 4L will be
  • 2R
  • R
  • R/2
  • R/4
It is easier to start a car engine on a hot day than on a cold day. This is because the internal resistance of the car battery
  • Decreases with rise in temperature
  • Increases with rise in temperature
  • Decreases with a fall in temperature
  • Does not change with a change in temperature
5 ampere of current is passed through a metallic conductor. The charge flowing in one minute in coulomb will be
  • 5
  • 12
  • 1/12
  • 300
A metal wire is subjected to a constant potential difference. When the temperature of the metal wire increases, the drift velocity of the electron in it
  • Increases, thermal velocity of the electron increases
  • Decreases, thermal velocity of the electron increases
  • Increases, thermal velocity of the electron decreases
  • Decreases, thermal velocity of the electron decreases
An electric wire is connected across a cell of e.m.f. E. The current I is measured by an ammeter of resistance R. According to ohm\'s law
  • E = I2R
  • E = IR
  • E = R/I
  • E = I/R
The resistances of a wire at temperatures t° C and 0° C are related by

  • Physics-Current Electricity I-64891.png
  • 2)
    Physics-Current Electricity I-64892.png

  • Physics-Current Electricity I-64893.png

  • Physics-Current Electricity I-64894.png
An electric wire of length ‘L’ and area of cross-section a has a resistance R ohm. Another wire of the same material having same length and area of cross-section 4a has a resistance of
  • 4R
  • R/4
  • R/16
  • 16R
For which of the following the resistance decreases on increasing the temperature?
  • Copper
  • Tungsten
  • Germanium
  • Aluminum
If n, e, τ and m respectively represent the density, charge relaxation time and mass of the electron, then the resistance of a wire of length land area of cross-section A will be

  • Physics-Current Electricity I-64896.png
  • 2)
    Physics-Current Electricity I-64897.png

  • Physics-Current Electricity I-64898.png

  • Physics-Current Electricity I-64899.png
Which of the following statements is correct?
  • Liquids obey fully the ohm's law
  • Liquids obey partially the ohm's law
  • There is no relation between current and p.d. for liquids
  • None of the above
A certain piece of silver of given mass is to be made like a wire. Which of the following combinations of length (L) and the area of cross-section (A) will lead to the smallest resistance
  • L and A
  • 2L and A/2
  • L/2 and 2A
  • Any of the above, because volume of silver remains same
A metal wire of specific resistance 64 × 10–6 ohm-cmand length 198 cm has a resistance of 7 ohm, the radius of the wire will be
  • 2.4 cm
  • 0.24 cm
  • 0.024 cm
  • 24 cm
For a metallic wire, the ratio V/i (V = the applied potential difference, i = current flowing) is
  • Independent of temperature
  • Increases as the temperature rises
  • Decreases as the temperature rises
  • Increases or decreases as temperature rises, depending upon the metal
All of the following statements are true except
  • Conductance is the reciprocal of resistance and is measured in Siemen
  • Ohm's law is not applicable at very low and very high temperatures
  • Ohm's law is applicable to semiconductors
  • Ohm's law is not applicable to electron tubes, discharge tubes and electrolytes
A potential difference of V is applied at the ends of a copper wire of length land diameter d. On doubling only d, drift velocity
  • Becomes two times
  • Becomes half
  • Does not change
  • Becomes one fourth
If the resistance of a conductor is 5 Ω at 50°C and 7Ω at 100°C, then the mean temperature coefficient of resistance of the material is
  • 0.008/°C
  • 0.006/°C
  • 0.004/°C
  • 0.0011°C
The resistance of a discharge tube is
  • Ohmic
  • Non-ohmic
  • Both (a) and (b)
  • Zero
We are able to obtain fairly large currents in a conductor because
  • The electron drift speed is usually very large
  • The number density of free electrons is very high and this can compensate for the low values of the electron drift speed and the very small magnitude of the electron charge
  • The number density of free electrons as well as the electron drift speeds are very large and these compensate for the very small magnitude of the electron charge
  • The very small magnitude of the electron charge has to be divided by the still smaller product of the number density and drift speed to get the electric current
In a wire of circular cross-section with radius r, free electrons travel with a drift velocity V when a current Iflows through the wire. What is the current in another wire of half the radius and of the same material when the drift velocity is 2V ?
  • 2I
  • I
  • I/2
  • I/4
The resistivity of a wire depends on its
  • Length
  • Area of cross-section
  • Shape
  • Material
The conductivity of a superconductor is
  • Very small
  • Infinite
  • Very large
  • Zero
In a neon discharge tube 2.9 × 1018 Ne+ ions move to the right each second while 1.2 × 1018, electrons move to the left per second. Electron charge is 1.6 × 10–19C.
The current in the discharge tube
  • 1 A towards right
  • 0.66 A towards right
  • 0.66 A towards left
  • Zero
The resistivity of alloys = Ralloy;the resistivity ofconstituent metals Rmetal . Then, usually
  • Ralloy = Rmetal
  • Ralloy< Rmetal
  • There is no simple relation between Ralloy andRmetal
  • Ralloy>Rmetal
Two wires A and B of same material and same mass have radii 2r and r respectively. If resistance of wire A is 34 Ω, then resistance of B will be
  • 544 Ω
  • 272 Ω
  • 68 Ω
  • 17 Ω
Two rods of same material and length have their electric resistances in ratio 1:2. When both rods are dipped in water, the correct statement will be
  • A has more loss of weight
  • B has more loss of weight
  • Both have same loss of weight
  • Loss of weight will be in the ratio 1: 2
Two different conductors have same resistance at 0°C. It is found that the resistance of the first conductor at t1° C is equal to the resistance of the second conductor at t2° C. The ratio of the temperature coefficients of resistance of the conductors, α1/α2 is

  • Physics-Current Electricity I-64913.png
  • 2)
    Physics-Current Electricity I-64914.png

  • Physics-Current Electricity I-64915.png

  • Physics-Current Electricity I-64916.png
The resistance of a wire at room temperature 30° C is found to be 10 Ω. Now to increase the resistance by 10%, the temperature of the wire must be [The temperature coefficient of resistance of the material ofthe wire is 0.002 per °C]
  • 36°C
  • 83°C
  • 63°C
  • 33° C
A current I is passing through a wire having two sections P and Q of uniform diameters d and d/2 respectively. If the mean drift velocity of electrons in sections P and Q is denoted by vP and vQ respectively,then

  • Physics-Current Electricity I-64919.png
  • 2)
    Physics-Current Electricity I-64920.png

  • Physics-Current Electricity I-64921.png

  • Physics-Current Electricity I-64922.png
If an electric current is passed through a nerve of a man, then man
  • Begins to laugh
  • Begins to weep
  • Is excited
  • Becomes insensitive to pain
The mobility of free electrons (charge e, mass m and relaxation time T) in a metal is proportional to

  • Physics-Current Electricity I-64924.png
  • 2)
    Physics-Current Electricity I-64925.png

  • Physics-Current Electricity I-64926.png

  • Physics-Current Electricity I-64927.png
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
  • 2 ohm
  • 3 ohm
  • 4 ohm
A block has dimensions 1 cm, 2 cm, 3 cm. Ratio of the maximum resistance to minimum resistance between any point of opposite faces of this block is
  • 9 : 1
  • 1 : 9
  • 18 : 1
  • 1 : 6
A rod of a certain metal is 1.0 m long and 0.6 cm in diameter. Its resistance is 3.0 ×10–3 ohm. Another disc made of the same metal is 2.0 cm in diameter and 1.0 mm thick. What is the resistance between theround faces of the disc?
  • 1.35 × 10–5Ω
  • 2.70 × 10–7
  • 4.05 × 10–6Ω
  • 8.10 × 10–5Ω
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 × 10–3per ° C)
  • 400°C
  • 450°C
  • 500°C
  • 550°C
An electron revolves 6 × 1015times/sec in circular loop.The current in the loop is
  • 0.96 mA
  • 0.96 μA
  • 28.8 A
  • None of these
The electron drift speed is small and the charge of the electron is also small but still, we obtain large currentin a conductor. This is due to
  • The conducting property of the conductor
  • The resistance of the conductor is small
  • The electron number density of the conductor is small
  • The electron number density of the conductor is enormous
If potential V = 100 ± 0.5 Voltand currentI = 10 ± 0.2 amp are given to us, then what will be thevalue of resistance?
  • 10 ± 0.7 Ω
  • 5 ± 2 Ω
  • 0.1 ± 0.2 Ω
  • None of these
A nichrome wire 50 cm long and one square millimetre cross-section carries a current of 4A when connected to a 2V battery. The resistivity of nichrome wire in ohmmetre is
  • 1 × 10–6
  • 4 × 10–7
  • 3 × 10–7
  • 2 × 10–7
If an observer is moving with respect to a stationaryelectron, then he observes
  • Only magnetic field
  • Only electric field
  • Both (a) and (b)
  • None of these
Calculate the amount of charge flowing in 2 minutes in a wire of resistance 10 Ω when a potential difference of20 V is applied between its ends
  • 120 C
  • 240 C
  • 20 C
  • 4 C
The number of free electrons per 100 mm of ordinary copper wire is 2 × 1021. Average drift speed of electrons is 0.25 mm/s. The current flowing is
  • 5 A
  • 80 A
  • 8 A
  • 0.8 A

Physics-Current Electricity I-64937.png

  • Physics-Current Electricity I-64938.png
  • 2)
    Physics-Current Electricity I-64939.png

  • Physics-Current Electricity I-64940.png

  • Physics-Current Electricity I-64941.png
The drift velocity does not depend upon
  • Cross-section of the wire
  • Length of the wire
  • Number of free electrons
  • Magnitude of the current
0:0:1


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