Current Drift Velocity & Mobility — Practice Questions

Free NEET Physics multiple-choice questions on Current Drift Velocity & Mobility. Attempt each question and reveal the answer with a full explanation.

A galvanometer of resistance G is converted into an ammeter using a shunt of resistance S . The effective resistance of the ammeter is: GS/(G+S) G+S G-S G S A galvanometer has a resistance of 100 and a full scale deflection for 2 mA . The value of resistance to be connected in series to convert it into a voltmeter of range 0-10 V is: 4900 5000 5100 4800 The relaxation time in conductors: Decreases with increase of temperature Increases with increase of temperature Is independent of temperature Depends on the length of the conductor The resistivity of a semiconductor at room temperature: Decreases with increase in temperature Increases with increase in temperature Remains constant First increases then decreases The electric field intensity E , current density J and specific resistance are related as: J = E/ E = J/ J = E J = E 2 A charged particle having drift velocity of 7.5 10 -4 m/s in an electric field of 3 10 -10 V/m , has a mobility in m 2 V -1 s -1 of: 2.5 10 6 2.5 10 -6 2.25 10 -15 2.25 10 15 Mobility of electrons in a conductor is defined as: Drift velocity per unit electric field Current per unit area Resistance per unit length Relaxation time per unit mass A steady current flows through a metallic conductor of non-uniform cross-section. Which of the following quantities is/are constant along the conductor? Current only Current and current density Current and drift speed Current, drift speed and electric field If a current is passed through a cylinder of a liquid, the liquid will: Expand Contract Remains same Rotate The mobility of free electrons in a conductor is proportional to: Relaxation time ( ) Electric field ( E ) Applied potential ( V ) Mass of the conductor ( M ) What is the order of magnitude of the drift velocity of electrons in a typical copper wire carrying a few amperes of current? 10 -4 m/s 10 6 m/s 10 8 m/s 10 2 m/s The drift velocity v d of free electrons in a metallic conductor varies with the intensity of the applied electric field E as: v d E v d E v d E 2 v d 1/E When a current is passed through a semiconductor, the density of charge carriers increases. This is because: Thermal energy breaks covalent bonds Drift velocity increases Electric field decreases The material expands Which of the following is true regarding the drift velocity v d of electrons and the thermal velocity v t of electrons in a metal at room temperature? v d v t v d v t v d v t v d = 0 According to the drift model of conductors, if the relaxation time decreases, the resistivity of the conductor: Increases Decreases Remains constant Becomes zero The drift velocity v d of electrons varies with the electric field E as: v d E v d E v d E 2 v d is independent of E The electrical resistivity of a semiconductor: Decreases with increase in temperature Increases with increase in temperature Increases with decrease in temperature Both (a) and (c) are correct If a current of 2 A flows through a conductor for 10 minutes , the total number of electrons passing through the conductor is approximately: 7.5 10 21 1.2 10 19 6.25 10 18 1.5 10 23 The relaxation time of electrons in a metal: Decreases with increase in temperature Increases with increase in temperature Is independent of temperature Is independent of the nature of the metal The mobility of charge carriers increases with: Increase in relaxation time Increase in electric field Decrease in relaxation time Increase in mass of the charge carrier A potential difference of 100 V is applied across a conductor of resistance 50 . The number of electrons flowing through any cross-section of the conductor per second is: 1.25 10 19 6.25 10 18 1.25 10 20 3.125 10 19 A 5 -ampere fuse wire can withstand a maximum power of 1 watt in the circuit. The resistance of the fuse wire is : 5 ohm 0.04 ohm 0.2 ohm 0.4 ohm When the current I flowing through a conductor of uniform cross-section is doubled, the drift velocity v d of the charge carriers: Is doubled Is halved Remains the same Becomes four times When a wire of uniform cross-section a, length and resistance R is bent into a complete circle, resistance between any two of diametrically opposite points will be - R/2 R/4 R/8 4R The mean free path of electrons in a metal is 4 10 -8 m . The electric field which can give on an average 2 eV energy to an electron in the metal will be in units of V/m : 5 10 7 8 10 7 5 10 -11 8 10 -11 A wire of resistance 4 is stretched to twice its original length. The resistance of stretched wire would be 2 4 8 16 Two cities are 150 km apart. Electric power is sent from one city to another city through copper wires. The fall of potential per km is 8 volt and the average resistance per km is 0.5 , the power loss in the wires is :- 19.2 W 19.2 kW 19.2 J 12.2 kW A carbon resistor of (47 4.7) k is to be marked with rings of different colours for its identification. The colour code sequence will be Yellow – Green – Violet – Gold Yellow – Violet – Orange – Silver Violet – Yellow – Orange – Silver Green – Orange – Violet – Gold A charged particle having drift velocity of 7.5 10 -4 m s -1 in an electric field of 3 10 -10 Vm -1 , has a mobility in m 2 V -1 s -1 of : 2.5 10 6 2.5 10 -6 2.25 10 -15 2.25 10 15 The color code of a resistance is given below The values of resistance and tolerance, respectively, are 47 k , 10% 4.7 k , 5% 470 , 5% 470 k , 5% Column-I gives certain physical terms associated with flow of current through a metallic conductor. Column-II gives some mathematical relations involving electrical quantities. Match Column-I and Column-II with appropriate relations. array ll Column-I & Column-II (A) Drift Velocity & (P) m ne 2 (B) Electrical Resistivity & (Q) nev d (C) Relaxation Period & (R) eE m (D) Current Density & (S) E J array (A) - (R), (B) - (S), (C) - (Q), (D) - (P) (A) - (R), (B) - (P), (C) - (S), (D) - (Q) (A) - (R), (B) - (Q), (C) - (S), (D) - (P) (A) - (R), (B) - (S), (C) - (P), (D) - (Q) Two resistors of resistance, 100 and 200 are connected in parallel in an electrical circuit. The ratio of the thermal energy developed in 100 to that in 200 in a given time is 2 : 1 1 : 4 4 : 1 1 : 2 Resistance of a carbon resistor determined from colour codes is (22000 5 %) . The colour of third band must be Red Green Orange Yellow The electrical conductivity of a metallic conductor depends on which of the following factors? Nature of the material and temperature Dimensions of the conductor only Applied potential difference across the conductor Shape of the cross-section of the conductor The resistance of platinum wire at 0 C is 2 and 6.8 at 80 C . The temperature coefficient of resistance of the wire is 3 10 -4 C -1 3 10 -3 C -1 3 10 -2 C -1 3 10 -1 C -1 A wire of resistance R is cut into 8 equal pieces. From these pieces two equivalent resistances are made by adding four of these together in parallel. Then these two sets are added in series. The net effective resistance of the combination is: R 8 R 64 R 32 R 16 A room heater is rated 400 W, 220 V. If the supply voltage drops to 200 V, what will be the power consumed (approximately)? 400 W 121 W 331 W 200 W Which of the following graphs represents the variation of resistivity ( ) with temperature (T) for copper? A curve starting from a non-zero value and increasing exponentially. A straight line with a positive slope. A straight line with a negative slope. A rectangular hyperbola. The drift velocity of electrons in a conductor is v d when the current is I . If the wire is replaced by another wire of same material but double the radius, and the current remains same, the new drift velocity will be: v d/4 v d/2 4v d 2v d Across a metallic conductor of non-uniform cross-section, a constant potential difference is applied. The quantity which remains constant along the conductor is: Current Drift velocity Electric field Current density A galvanometer has a coil of resistance 100 and gives a full scale deflection for 30 mA current. If it is to work as a voltmeter of 30 V range, the resistance required to be added will be: 900 in series 900 in parallel 1800 in series 1800 in parallel A galvanometer having a resistance of 9 is shunted by a wire of resistance 2 . If the total current is 1 A , the part of it passing through the shunt will be: 0.81 A 0.19 A 0.5 A 0.2 A Potential difference V is applied across a conductor of length L and diameter D . If the diameter is halved and length is doubled, the drift velocity of free electrons will: Be halved Be doubled Remain same Be quadrupled A 5 C rise in temperature is observed in a conductor by passing a current. When the current is doubled, the rise in temperature will be: 20 C 10 C 40 C 25 C The 'Figure of Merit' of a galvanometer is 0.5 A/division . If the galvanometer scale has 30 divisions on either side of the zero, the current required for full-scale deflection is: 15 A 30 A 60 A 0.5 mA The drift velocity of free electrons in a conductor is v d . If the potential difference across the conductor is doubled and the length of the conductor is halved, the new drift velocity will be: 4v d 2v d v d 4 v d A galvanometer of resistance G is converted into a voltmeter of range 0-V volts by connecting a resistance R in series. To increase the range to 0-2V , the additional resistance to be connected in series is: R+G R G 2R If the number of turns in a galvanometer coil is doubled, then: Current sensitivity is doubled but voltage sensitivity remains same Both current and voltage sensitivity are doubled Current sensitivity remains same but voltage sensitivity is doubled Both current and voltage sensitivity remain same A potential difference of V is applied at the ends of a copper wire of length l and diameter d . On doubling only d , the drift velocity: Remains same Becomes double Becomes half Becomes one-fourth The current sensitivity of a moving coil galvanometer is 5 div/mA and its voltage sensitivity is 20 div/V . The resistance of the galvanometer is: 250 25 500 4 The current in a wire varies with time as I = 2 + 3t , where I is in amperes and t is in seconds. The quantity of charge passing through a cross-section of the wire during t = 0 to t = 2 s is: 10 C 6 C 5 C 12 C An ammeter of range 1 A has a resistance of 0.9 . To increase its range to 10 A , the required shunt is: 0.1 0.01 0.9 1 If the current sensitivity of a moving coil galvanometer is increased by 20 % , and its resistance is increased such that the voltage sensitivity remains constant, by what percentage did the resistance increase? 20 % 10 % 25 % 50 % A galvanometer of resistance 100 gives full scale deflection for 10 mA current. To use it as an ammeter of range 0-10 A , the resistance of the shunt required is: 0.1001 0.111 0.01 1.0 A potential difference of V is applied across a copper wire of length L and diameter d . If the diameter of the wire is doubled, the drift velocity of electrons: Remains unchanged Is doubled Is halved Becomes one-fourth When a steady current flows through a metallic conductor, heat is produced. This heating effect is primarily due to: Collisions of free electrons with the lattice ions Energy lost by electrons during acceleration in the field Release of energy during the formation of covalent bonds Increase in the magnetic potential energy of the conductor A potential difference V is applied to a copper wire of length l and thickness d . If V is kept constant and l is doubled, the drift velocity of electrons will: Become half Be doubled Remain the same Become quadruple The electrical conductivity of a semiconductor increases with temperature because: The number density of free charge carriers increases significantly. The relaxation time increases. The mass of the charge carriers decreases. The atoms vibrate with smaller amplitude. The 'Figure of Merit' of a galvanometer is defined as: Current required to produce a deflection of one scale division Voltage required for full scale deflection Reciprocal of current sensitivity Resistance of the galvanometer coil A galvanometer has a resistance of 50 and a full-scale deflection current of 1 mA . To convert it into a voltmeter of range 10 V , the resistance to be added in series is: 9950 10000 995 50 In the microscopic model of Ohm's law, the current density J is related to the electric field E and the relaxation time as: J = ne 2 m E J = ne m E J = ne 2 2 m E J = m ne 2 E A cell of EMF E is connected across a conductor of length l . If the length of the conductor is tripled (keeping E constant) by stretching it, the drift velocity of electrons will: Become one-third Become triple Become nine times Remain unchanged A galvanometer with a scale divided into 100 equal divisions has a current sensitivity of 10 divisions per mA and a voltage sensitivity of 2 divisions per mV . The resistance of the galvanometer is: 5 20 50 2 A copper wire is subjected to a constant potential difference. As the temperature of the wire increases, the drift velocity of the electrons: Decreases Increases Remains the same First increases then decreases A galvanometer has a resistance of 30 and a current of 2 mA is needed to give full scale deflection. What is the resistance needed and how is it connected to convert it into an ammeter of 0.3 A range? 0.2 in parallel 0.2 in series 150 in parallel 150 in series When the temperature of a metallic conductor is increased, keeping the applied potential difference constant, the drift velocity of electrons: Decreases Increases Remains constant First increases then decreases A galvanometer of resistance G is shunted by a resistance S . The percentage of the total current that passes through the shunt is: G G+S 100 S G+S 100 G S 100 S G 100 A steady current of 5 A passes through a metallic wire of 0.04 m 2 cross-sectional area. If the electric field inside the wire is 5 V/m , the electrical conductivity of the material is: 25 -1 m -1 0.04 -1 m -1 125 -1 m -1 6.25 -1 m -1 A copper wire is subjected to a constant potential difference. If the temperature of the wire increases due to Joule heating, which of the following quantities remains unchanged? The number of free electrons per unit volume The drift velocity of electrons The electrical resistance The relaxation time of electrons For a metallic conductor, the plot of the product of resistivity ( ) and conductivity ( ) versus temperature ( T ) is: A horizontal straight line A straight line passing through the origin An exponential curve A hyperbola The relaxation time 0311 of electrons in a metal depends on: Nature of material and temperature Applied electric field Dimensions of the conductor Potential difference across the conductor A potential difference V is applied across a copper wire. If the temperature of the wire is increased, the drift velocity of the electrons will: Decrease Increase Remain same First increase then decrease Two circular coil 1 and 2 are made from the same wire but the radius of the 1 st coil is twice that of the 2 nd coil. What potential difference in volts should be applied across them so that the magnetic field at their centres is the same- 3 4 6 2 A wire of resistance 12 ohms per metre is bent to form a complete circle of radius 10 cm. The resistance between its two diametrically opposite points, A and B as shown in the figure, is : 6 0.6 3 6 The charge flowing through a resistance R varies with time t as Q = at - bt 2 , where a and b are positive constants. The total heat produced in R is: a 3R 6b a 3R 3b a 3R 2b a 3R b Which of the following graph represents the variation of resistivity ( ) with temperature (T) for copper? A copper wire of length 10 m and radius ( 10 -2 ) m has electrical resistance of 10 . The current density in the wire for an electric field strength of 10 (V/m) is 10 6 A/m 2 10 -5 A/m 2 10 5 A/m 2 10 4 A/m 2 Which of the following materials has a resistivity that decreases nearly exponentially with increasing temperature? Germanium Silver Copper Nichrome A wire of length ‘ l ’ and resistance 100 is divided into 10 equal parts. The first 5 parts are connected in series while the next 5 parts are connected in parallel. The two combinations are again connected in series. The resistance of this final combination is: 26 52 55 60 Two heaters A and B have power rating of 1 kW and 2 kW , respectively. Those two are first connected in series and then in parallel to a fixed power source. The ratio of power outputs for these two cases is: 1 : 1 2 : 9 1 : 2 2 : 3 Ten identical cells connected in series are needed to heat a wire of length L and radius r by 10 C in time t . How many cells will be required to heat the wire of same material, same length but double the radius by the same temperature in the same time? (Internal resistance is negligible) 5 10 20 40 A galvanometer of resistance 50 is connected to a battery of 3 V along with a resistance of 2950 in series. A full scale deflection of 30 divisions is obtained. In order to reduce this deflection to 20 divisions, the resistance in series should be: 4450 5050 6050 4400 Dimensions of electrical mobility are: [M -1 L 0 T 2 A 1] [M -1 L 1 T 2 A 1] [M L -2 T 3 A -1 ] [M -1 L 0 T 3 A 1] A galvanometer of resistance G is shunted by a resistance S . To keep the main current in the circuit unchanged, the resistance to be put in series with the galvanometer is: G 2 / (G + S) S 2 / (G + S) SG / (G + S) G / (G + S) The current I through a conductor varies with time t as I = I 0 ( t) . The total charge that flows through the conductor in the time interval t=0 to t= / is: 2I 0/ I 0/ I 0/ 0 The current density J in a cylindrical wire of radius R varies with the radial distance r from the axis as J = J 0(1 - r/R) . The total current in the wire is: R 2 J 0 / 3 R 2 J 0 / 2 2 R 2 J 0 / 3 R 2 J 0 The electrical conductivity of a semiconductor increases when electromagnetic radiation of wavelength shorter than 2480 nm is incident on it. The band gap for the semiconductor is approximately: 0.5 eV 0.7 eV 1.1 eV 2.5 eV The current-voltage ( I-V ) graph for a certain device is a non-linear curve. This indicates that the device is: Non-Ohmic Ohmic A perfect conductor An insulator