Current Electricity PYQs Set 9 (PDF)

Set 9 of 21 · Questions 241-270 of 612

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Mere Teacher · Previous Year Questions NEET Physics · Current Electricity · Set 9 (Q241-270)
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241. $Incandescent bulbs are designed by keeping in mind that the resistance of their filament increases with increase in temperature. If at room temperature, 100 W, 60 W and 40 W bulbs have filament resistances R_{100}, R_{60} and R_{40}, respectively, the relation between these resistance is$ (1) $\frac{1}{R _{100}} = \frac{1}{R _{40}} + \frac{1}{R _{60}}$ (2) $R_{100} = R_{40} + R_{60}$ (3) $R_{100} > R_{60} > R_{40}$ (4) $\frac{1}{R _{100}} > \frac{1}{R _{60}} > \frac{1}{R _{40}}$ 242. $When a potential difference V is applied across a wire of resistance R, it dissipates energy at a rate W. If the wire is cut into two halves and these halves are connected mutually parallel across the same supply, the same supply, the energy dissipation rate will become:$ (1) $1/4 W$ (2) $1/2 W$ (3) $2 W$ (4) $4 W$ 243. $A 72 Ω galvanometer is shunted by a resistance of 8 Ω . The percentage of the total current which passes through the galvanometer is:$ (1) $0.1%$ (2) $10%$ (3) $25%$ (4) $0.25%$ 244. $Drift speed of electrons, when 1.5A of current flows in a copper wire of cross section 5 m m^{2}, is v. If the electron density in copper is 9 \times 1 0^{28} / m^{3} the value of v in mm/s is close to (Take charge of electron to be = 1.6 \times 1 0^{- 19} C)$ (1) $0.2$ (2) $3$ (3) $2$ (4) $0.02$ 245. $A wire of length 10 cm and radius 7 \times 10^{- 4} m connected across the right gap of a meter bridge. When a resistance of 4.5Ω is connected on the left gap by using a resistance box, the balance length is found to be at 60 cm from the left end. If the resistivity of the wire is R \times 10^{- 7} Ωm, then value of R is:$ (1) $63$ (2) $70$ (3) $66$ (4) $35$ 246. $A copper wire of length 1 m and uniform cross-sectional area 5 \times 10^{- 7} m^{2} carries a current of 1 A . Assuming that there are 8 \times 10^{28} free electrons per m^{3} in copper, how long will an electron take to drift from one end of the wire to the other?$ (1) $0.8 \times 10^{3} s$ (2) $1.6 \times 10^{3} s$ (3) $3.2 \times 10^{3} s$ (4) $6.4 \times 10^{3} s$ 247. $A material ‘B’ has twice the specific resistance of ‘A’. A circular wire made of ‘B’ has twice the diameter of a wire made of ‘A’. Then for the two wires to have the same resistance, the ratio l_{A} / l_{B} of their respective lengths must be$ (1) $2$ (2) $1$ (3) $1/2$ (4) $1/4$ 248. $Two solid conductors are made up of same material, have same length and same resistance. One of them has a circular cross-section of area A_{1} and the other one has a square cross-section of area A_{2} . The ratio A_{1} / A_{2} is [NEET 2020]$ (1) $1.5$ (2) $1$ (3) $0.8$ (4) $2$ 249. $When a resistance R_{1} is connected across a cell, the current is I_{1} and if the resistance R_{1} is replaced by R_{2}, the current is I_{2} . Then the internal resistance of the cell is$ (1) $\frac{I _{1} R _{1} + I _{2} R _{2}}{I _{1} + I _{2}}$ (2) $\frac{I _{1} R _{2} - I _{2} R _{1}}{I _{1} - I _{2}}$ (3) $I1R2+I2R1I1-I2$ (4) $\frac{I _{2} R _{2} - I _{1} R _{1}}{I _{1} - I _{2}}$ 250. $Two unknown resistances are connected in two gaps of a meter-bridge. The null point is obtained at 40 cm from left end. A 30Ω resistance is connected in series with the smaller of the two resistances, the null point shifts by 20 cm to the right end. The value of smaller resistance in Ω is$ (1) $12$ (2) $24$ (3) $36$ (4) $48$ 251. $Current passing through a wire as function of time is given as I (t) = 0.02 t + 0.01 A . The charge that will flow through the wire from t = 1 s to t = 2 s is$ (1) $0.02 C$ (2) $0.07 C$ (3) $0.06 C$ (4) $0.04 C$ 252. $The walls of a closed cubical box of edge 60 cm are made of material of thickness 1 mm and thermal conductivity, 4 \times 10^{- 4} cal s^{- 1} cm^{- 1}^{\circ} C^{- 1} . The interior of the box is maintained 1000^{\circ} C above the outside temperature by a heater placed inside the box and connected across 400 V DC supply. The resistance of the heater is$ (1) $4.41Ω$ (2) $44.1Ω$ (3) $0.441Ω$ (4) $441Ω$ 253. $Two wires made of the same material have lengths in the ratio 2 : 3 and radii in the ratio 8 : 9 . If the same potential difference is applied across the ends of the wires, the ratio of the electric currents flowing through them is$ (1) $5 : 6$ (2) $6 : 5$ (3) $4 : 3$ (4) $32 : 27$ 254. $A piece of copper and another of germanium are cooled from room temperature to 77^{\circ} K . The resistance of$ (1) $copper increases and germanium decreases$ (2) $both decreases$ (3) $both increases$ (4) $copper decreases and germanium increases$ 255. $A piece of copper is to be shaped into a conducting wire of maximum resistance. The suitable length and diameter are and respectively.$ (1) $L and d$ (2) $2L and d/2$ (3) $L/2 and 2d$ (4) $2L and d$ 256. $Which of the following statements is false?$ (1) $Krichhoff's second law represents energy conservation.$ (2) $Wheatstone bridge is the most sensitive when all the four resistance are of the same order of magnitude$ (3) $In a balanced wheatstone bridge if the cell and the galvanometer are exchanged, the null point is disturbed$ (4) $A rheostat can be used as a potential divider.$ 257. $The electric current through a wire varies with time as I = I_{0} + β t. where I_{0} = 20 A and β = 3 A / s . The amount of electric charge crossed through a section of the wire in 20 s is:$ (1) $80 C$ (2) $1000 C$ (3) $800C$ (4) $1600 C$ 258. $In potentiometer experiment, null point is obtained at a particular point for a cell on potentiometer wire x cm long. If the length of the potentiometer wire is increased without changing the cell, the balancing length will (Driving source is not changed)$ (1) $increase$ (2) $decrease$ (3) $not change$ (4) $becomes zero$ 259. $Resistance of a given wire is obtained by measuring the current flowing in it and the voltage difference applied across it. If the percentage errors in the measurement of the current and the voltage difference are 3% each, then error in the value of resistance of the wire is:$ (1) $6%$ (2) $zero$ (3) $1%$ (4) $3%$ 260. $The equivalent resistance of two resistors connected in series is 6Ω and their parallel equivalent resistance is \frac{4}{3} Ω . What are the values of resistances?$ (1) $4Ω, 2Ω$ (2) $4Ω, 6Ω$ (3) $6Ω, 2Ω$ (4) $8Ω, 1Ω$ 261. $A student measures the terminal potential difference (V) of a cell (of emf ε and internal resistance r) as a function of the current (I) flowing through it. The slope and intercept of the graph between V and I, then respectively. equal$ (1) $ε and -r$ (2) $-r and ε$ (3) $r and - ε$ (4) $- ε and r$ 262. $Across a metallic conductor of non-uniform cross-section, a constant potential difference is applied. The quantity which remain constant along the conductor is$ (1) $current density$ (2) $current$ (3) $drift velocity$ (4) $electric field$ 263. $An electric kettle has two heating coils. When one of the coils is connected to an a . c . source, the water in the kettle boils in 10 minutes. When the other coil is used the water boils in 40 minutes. If both the coils are connected in parallel, the time taken by the same quantity of water to boil will be$ (1) $8 minutes$ (2) $4 minutes$ (3) $25 minutes$ (4) $15 minutes$ 264. $A conductor of length 100 cm and area of cross-section 1 mm^{2} carries a current of 5 A . If the resistivity of the material of the conductor is 3.0 \times 10^{- 8} Ω - m, then the electric field across the conductor is$ (1) $0.15 V / m$ (2) $0.015 V / m$ (3) $1.5 V / m$ (4) $0.0015 V / m$ 265. $A wire of aluminium and a wire of germanium are cooled to a temperature of 77 K . Then$ (1) $resistance of each of them decreases$ (2) $resistance of each of them increases$ (3) $resistance of aluminium wire increases and that of germanium wire decreases$ (4) $resistance of aluminium wire decreases and that of germanium wire increases$ 266. $Kirchhoff’s first and second laws of electrical circuits are consequences of$ (1) $conservation of energy and electric charge respectively$ (2) $conservation of energy$ (3) $conservation of electric charge and energy respectively$ (4) $conservation of electric charge.$ 267. $Equivalent resistance between the adjacent corners of a regular n-sided polygon of uniform wire of resistance R would be:$ (1) $\frac{( n - 1 ) R}{n ^{2}}$ (2) $\frac{( n - 1 ) R}{2 n - 1}$ (3) $\frac{n ^{2} R}{n - 1}$ (4) $\frac{( n - 1 ) R}{n}$ 268. $The current passing through the ideal ammeter in the circuit given below is$ (1) $1.25 A$ (2) $1 A$ (3) $0.75 A$ (4) $0.5 A .$ 269. $A potentiometer wire AB having length L and resistance 12 r is joined to a cell D of emf ε and internal resistance r. A cell C having emf ε/2 and internal resistance 3r is connected. The length AJ at which the galvanometer as shown in figure. shows no deflection is:$ (1) $\frac{5}{12} L$ (2) $\frac{11}{24} L$ (3) $\frac{11}{12} L$ (4) $\frac{13}{24} L$ 270. $A battery with internal resistance of 4Ω is connected to a circuit consisting three resistances, R, 2 R and 4 R (see following figure). If the power generated in the circuit is highest, then the magnitude of R must be$ (1) $4Ω$ (2) $7Ω$ (3) $10Ω$ (4) $14Ω$