CBSE Class 12 Physics Current Electricity Assignment Set B

Answer: B

Question. A carbon resistor of (47 ± 4.7) kW is to be marked with rings of different colours for its identification.    
The colour code sequence will be
(a) Violet – Yellow – Orange – Silver
(b) Yellow – Violet – Orange – Silver
(c) Yellow – Green – Violet – Gold
(d) Green – Orange – Violet – Gold 

Answer: B

Question. The solids which have the negative temperature coefficient of resistance are    
(a) metals
(b) insulators only
(c) semiconductors only
(d) insulators and semiconductors. 

Answer: D

Question. Specific resistance of a conductor increases with    
(a) increase in temperature
(b) increase in cross-section area
(c) increase in cross-section and decrease in length
(d) decrease in cross-section area. 

Answer: A

Question. Copper and silicon is cooled from 300 K to 60 K, the specific resistance     
(a) decreases in copper but increases in silicon
(b) increases in copper but decreases in silicon
(c) increases in both
(d) decreases in both.

Answer: A

Question. Which of the following acts as a circuit protection device?   
(a) fuse
(b) conductor
(c) inductor
(d) switch

Answer: A

Question. The charge flowing through a resistance R varies with time t as Q = at – bt2, where a and b are positive constants. The total heat produced in R is    
(a) a3 R /2b
(b) a3 R /b
(c) a3 R /6b
(d) a3 R / 3b

Answer: C

Question. A wire 50 cm long and 1 mm2 in cross-section carries a current of 4 A when connected to a 2 V battery. The resistivity of the wire is   
(a) 4 × 10^–6 W m
(b) 1 × 10^–6 W m
(c) 2 × 10^–7 W m
(d) 5 × 10^–7 W m 

Answer: B

Question. A wire of a certain material is stretched slowly by ten percent. Its new resistance and specific resistance become respectively  
(a) both remain the same
(b) 1.1 times, 1.1 times
(c) 1.2 times, 1.1 times
(d) 1.21 times, same 

Answer: D

Question. The masses of the wires of copper is in the ratio of 1 : 3 : 5 and their lengths are in the ratio of 5 : 3 : 1. The ratio of their electrical resistance is   
(a) 1 : 3 : 5
(b) 5 : 3 : 1
(c) 1 : 25 : 125
(d) 125 : 15 : 1

Answer: D

Question. Three resistances each of 4 W are connected to form a triangle. The resistance between any two terminals is    
(a) 12 W
(b) 2 W
(c) 6 W
(d) 8/3 W

Answer: D

Question. 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 W. The power loss in the wire is
(a) 19.2 W
(b) 19.2 kW
(c) 19.2 J
(d) 12.2 kW

Answer: B

Question. The resistance of a wire is ‘R’ ohm. If it is melted and stretched to ‘n’ times its original length, its new resistance will be   
(a) R /n
(b) n2R
(c) R /n2
(d) nR

Answer: B

Question. The equivalent resistance between A and B is
(a) 8R/5
(b) 5R/8
(c) 3R/8
(d) 7R/8

Answer: B

Question. Determine the current in 2Ω resistor. 

(a) 1 A
(b) 1.5 A
(c) 0.9 A
(d) 0.6 A

Answer: C

Question. Two heating wires of equal length are first connected in series and then in parallel to a constant voltage source.
The rate of heat produced in two cases is (parallel to series)
(a) 1 : 4
(b) 4 : 1
(c) 1 : 2
(d) 2 : 1

Answer: B

Question. The emf developed by a thermocouple is measured with the help of a potentiometer and not by a moving coil millivoltmeter because
(a) the potentiometer is more accurate than the voltmeter
(b) the potentiometer is more sensitive than voltmeter
(c) the potentiometer makes measurement without drawing any current from the thermocouple
(d) measurement using a potentiometer is simpler than with a voltmeter

Answer: C

Question. Who among the following scientists made the statement ?
“Chemical change can produce electricity”.
(a) Galvani
(b) Faraday
(c) Coulomb
(d) Thompson

Answer: A

Question. Two resistances R₁ and R₂ are made of different materials. The temperature coefficient of the material of R₁ is a and that of material of R₂ is – β . The resistance of the series combination of R₁ and R₂ will not change with temperatur if R₁/R₂ equal to
(a) α/β
(b) α + β/α - β
(c) α² + β²/2αβ
(d) β/α

Answer: D

Question. A wire of resistance 4 Ω is stretched to twice its original length. The resistance of stretched wire would be 
(a) 4 Ω
(b) 8 Ω
(c) 16 Ω
(d) 2 Ω

Answer: C

Question. The belt of an electrostatic generator is 50 cm wide and travels at 30 cm/sec. The belt carries charge into the sphere at a rate corresponding to 10^–4 ampere. What is the surface density of charge on the belt.
(a) 6.7 x 10^-5Cm^-2 / s
(b) 6.7 x 10^-4Cm^-2 / s
(c) 6.7 x 10^-7Cm^-2 / s
(d) 6.7 x 10^-8Cm^-2 /s

Answer: B

Question. The thermo e.m.f. of a thermocouple is 25mV/ºC at room temperature. A galvanometer of 40 ohm resistance, capable of detecting current as low as 10–5 A, is connected with the thermocouple. The smallest temperature difference that can be detected by this system is
(a) 12ºC
(b) 0ºC
(c) 20ºC
(d) 16ºC

Answer: D

Question. Resistances 1 Ω, 2 W and 3 Ω are connected to form a triangle. If a 1.5 V cell of negligible internal resistance is connected across the 3 Ω resistor, the current flowing through this resistor will be
(a) 0.25 A
(b) 0.5 A
(c) 1.0 A
(d) 1.5 A

Answer: B

Question. In the circuit , the galvanometer G shows zero deflection. If the batteries A and B have negligible internal resistance, the value of the resistor R will be 

(a) 100Ω
(b) 200Ω
(c) 1000Ω
(d) 500Ω

Answer: A

Question. The thermo e.m.f. of a thermocouple is given by E = 2164 t – 6.2 t². The neutral temperature and a temperature of inversion are
(a) 349, 174.5
(b) 174.5, 349
(c) 349, 698
(d) 698, 349

Answer: B

Question. One junction of a certain thermocouple is at a fixed temperature Tr and the other junction is at a temperature T. The electormotive force for this is expressed by, 

Answer: A

Question. The e.m.f. developed in a thermo-couple is given by E = α T + 1/2 βT² where T is the temperature of hot junction, cold junction being at 0ºC. The thermo electric power of the couple is 

Answer: B

Question. The thermo e.m.f. E in volts of a certain thermocouple is found to vary with temperature T of hot junction while cold junction is kept at 0ºC
E = 40 T - T2/20
The neutral temperature of the couple is
(a) 100ºC
(b) 200ºC
(c) 400ºC
(d) 800ºC

Answer: C

Question. 2, 4 and 6 S are conductances of three conductors. When they are joined in parallel, their equivalent conductance will be
(a) 12 S
(b) (1/12) S
(c) (12/11) S
(d) (11/12) S

Answer: A

Question. The numerical value of charge on either plate of capacitor C shown in figure is 

(a) CE
(b) CER₁/R₁+r
(c) CER₂/R₂+r
(d) CER₁/R₂+r

Answer: B

Question. If current flowing in a conductor changes by 1% then power consumed will change by
(a) 10%
(b) 2%
(c) 1%
(d) 100%

Answer: B

Question. A fuse wire with a radius of 1 mm blows at 1.5 A. If the fuse wire of the same material should blow at 3.0 A, the radius of the wire must be
(a) 4^1/3 mm
(b) √2 mm
(c) 0.5 mm
(d) 8.0 mm

Answer: A

Question. A 4 μ F conductor is charged 50 volts and then its plates are joined through a resistance of 1 k W. The heat produced in the resistance is
(a) 0.16 J
(b) 1.28 J
(c) 0.64 J
(d) 0.32 J

Answer: D

Question. Two bulbs of 500 W and 200 W are manufactured to operate on 220 V line. The ratio of heat produced in 500 W and 200 W, in two cases, when firstly they are connected in parallel and secondary in series will be
(a) 5/2 : 2/5
(b) 5/2 : 5/2
(c) 2/5 : 5/2
(d) 2/5 : 2/5

Answer: A

Question. A wire of resistance 20 W is covered with ice and a voltage of 210 V is applied across the wire, then rate of melting the ice is
(a) 0.85 g/s
(b) 1.92 g/s
(c) 6.56 g/s
(d) All of these

Answer: C

Question. Silver and copper voltameters are connected in parallel with a battery of e.m.f 12 V. In 30 minute 1 g of silver and 1.8 g of copper are liberated. The energy supplied by the battery is [ Z_Ag = 11.2 × 10^–4gc^–1; Z_Cu = 6.6 × 10^–4 gc^–1]
(a) 720 J
(b) 2.41 J
(c) 24.12 J
(d) 4.34 × 10⁴ J

Answer: D

Question. Which of the following is not reversible ?
(a) Joule effect
(b) Peltier effect
(c) Seebeck effect
(d) Thomson effect

Answer: A

Question. In the Seebeck series Bi occurs first followed by Cu and Fe among other. The Sb is the last in the series. If ζ₁ be the thermo emf at the given temperature difference for Bi – Sb thermocouple and ζ, be that for Cu-Fe thermocouple, which of the following is true?
(a) ζ₁ = ζ₂
(b) ζ₁ < ζ₂
(c) ζ₁ > ζ₂
(d) Data is not sufficient to predict it.

Answer: C