## THERMAL AND CHEMICAL EFFECTS OF CURRENTS mcq

*THERMAL AND CHEMICAL EFFECTS OF CURRENTS*

*1 ) A heater coil is cut into two equal parts and only one part is now used in the heater.*

*The heat generated will now be*

*( a ) four times*

*( b ) doubled*

*( c ) halved*

*( d ) one-fourth [ AIEEE 2005 ]*

*2 ) Time taken by a 836 W heater to heat one litre of water from 10° C to 40° C is*

*( a ) 50 s ( b ) 100 s ( c ) 150 s ( d ) 200 s [ AIEEE 2004 ]*

*3) The thermo-emf of a thermocouple varies with the temperature θ of the hot junction as*

*E = a θ + b θ2 in volts where the ratio a / b is 700° C. If the cold junction is kept at*

*0° C, then the neutral temperature is*

*( a ) 700° C*

*( b ) 350° C*

*( c ) 1400° C*

*( d ) no neutral temperature is*

*possible for this thermocouple*

*[ AIEEE 2004 ]*

*4 ) The electrochemical equivalent of metal is 3.3 × 10 - 7 kg per coulomb. The mass of the*

*metal liberated when a three ampere current is passed for 2 seconds will be*

*( a ) 19.8 × 10-7 kg*

*( b ) 9.9 × 10-7 kg*

*( c ) 6.6 × 10-7 kg*

*( d ) 1.1 × 10-7 kg [ AIEEE 2004 ]*

*5) A 220 volt, 1000 watt bulb is connected across 110 volt mains supply. The power*

*consumed will be*

*( a ) 1000 watt*

*( b ) 750 watt*

*( c ) 500 watt*

*( d ) 250 watt*

*[ AIEEE 2003 ]*

*6) An electric motor operates at 20 rev / sec. What will be the approximate power delivered*

*by the motor, if it supplies a torque of 75 N-m ?*

*( a ) 1550 W*

*( b ) 4040 W*

*( c ) 7730 W*

*( d ) 9420 W [ AIEEE 2003 ]*

*7 ) The negative Zn pole of a Daniell cell, sending a constant current through a circuit,*

*decreases in mass by 0.13 g in 30 minutes. If the electrochemical equivalents of Zn and*

*Cu are 32.5 and 31.5 respectively, then increase in the mass of positive Cu pole in this*

*time is*

*( a ) 0.242 g*

*( b ) 0.180 g*

*( c ) 0.141 g*

*( d ) 0.126 g [ AIEEE 2003 ]*

*8) 2 litre water kept in a kettle is heated by 1 KW power source. Kettle is open and it loses*

*heat at the rate of 160 J/s. The time taken for the temperature of kettle to change from*

*27° C to 77° C is*

*( a ) 8 min 20 sec*

*( b ) 6 min 20 sec*

*( c ) 5 min*

*( d ) 7 min [ IIT 2005 ]*

*9 ) An ideal gas enclosed in an insulated vessel is heated through a coil of resistance*

*100 Ω carrying current of 1 A for 5 minutes. Then change in its internal energy will be*

*( a ) 30 KJ*

*( b ) 20 KJ*

*( c ) 2 KJ*

*( d ) 3 KJ [ IIT 2005]*

*10 ) A wire of length L and 3 identical cells of negligible internal resistances are*

*connected in series. Due to the current, the temperature of the wire is raised by ΔT*

*in time t. A number N of similar cells is now connected in series with a wire of the*

*same material and cross-section but of length 2L. The emperature of the wire is*

*raised by the same amount ΔT in the same time. The value of N is*

*( a ) 4*

*( b ) 6*

*( c ) 8*

*( d ) 9 [ IIT 2001 ]*

*11) A constant voltage is applied between the two ends of a uniform metallic wire. Some*

*heat is developed in it. The heat developed is doubled if*

*( a ) both the length and the radius of the wire are halved*

*( b ) both the length and the radius of the wire are doubled*

*( c ) the radius of the wire is doubled*

*( d ) the length of the wire is doubled*

*12) Two resistors R1 and R2 when connected across 120 V consume power at the rate of*

*25 W and 100 W respectively when connected in series and parallel across the same*

*120 V line. Then the ratio of power consumed by R1 to that by R2 is*

*( a ) 1 : 1*

*( b ) 1 : 2*

*( c ) 2 : 1*

*( d ) 1 : 4*

*13) Find the power wasted in the transmission cables of resistance 0.05 Ω when 10 kW*

*is transmitted at 200 V.*

*( a ) 0.0125 kW*

*( b ) 0.125 kW*

*( c ) 25 kW*

*( d ) 37.5 kW*

*14 ) A house is served by a 220 V supply line. In a circuit protected by a fuse marked 9 A,*

*the maximum number of 60 W lamps in parallel that can be turned on is*

*( a ) 44*

*( b ) 22*

*( c ) 55*

*( d ) 33*

*15 ) A tap supplies water at 22° C. A man takes 1 litre of water per minute at 37° C from*

*the geyser. The power of geyser is*

*( a ) 2100 W*

*( b ) 725 W*

*( c ) 1050 W*

*( d ) 1575 W*

*16 ) A wire of uniform cross-section when connected directly across a 200 volt mains*

*produces x cal / s of heat. If the wire is cut into 10 parts of equal length which are*

*then connected in parallel to 100 volt mains, the heat produced in cal / s will be*

*( a ) 25 x*

*( b ) 50 x*

*( c ) 75 x*

*( d ) 100 x*

*17 ) The power of a heater is 500 W at 800° C. What will be its power at 200° C if*

*α = 4 × 10 - 4*

*per ° C ?*

*( a ) 484 W*

*( b ) 672 W*

*( c ) 526 W*

*( d ) 611 W*

*18 ) Material of heating element of electric heater should have*

*( a ) high resistivity and high melting point*

*( b ) high resistivity and low melting point*

*( c ) low resistivity and low melting point*

*( d ) low resistivity and high melting point*

*19 ) An electric kettle has two coils. When one is switched on, water in the kettle boils in 6*

*min. With the other it takes 3 min. When they are connected in series and used*

*together, time taken to reach the boiling point is x min. When both are used together*

*in parallel connection, time taken is y min. Then x / y =*

*( a ) 1*

*( b ) 2*

*( c ) 0.5*

*( d ) 4.5*

*20 ) Two heating wires have lengths in the ratio 1 : 2. They are used by first connecting in*

*series and then in parallel. The ratio of heat produced in the two cases will be*

*( a ) 2 : 5*

*( b ) 5 : 2*

*( c ) 2 : 9*

*( d ) 9 : 2*

*21 ) How much current should pass through acidulated water for 100 s to liberate 0.224 litre*

*of hydrogen ?*

*( a ) 22.4 A*

*( b ) 19.3 A*

*( c ) 9.65 A*

*( d ) 1 A*

*22) Which of the following is not reversible ?*

*( a ) Seebeck effect*

*( b ) Peltier effect*

*( c ) Joule’s effect*

*( d ) Thomson effect*

*23 ) A copper-iron thermocouple is connected to an external battery of emf E. On doubling*

*the emf of the battery, the heat produced at a junction*

*( a ) remains same*

*( b ) becomes half*

*( c ) doubles up*

*( d ) becomes four times*

*24 ) What is the nature of graph between temperature and thermo-emf ?*

*( a ) hyperbola*

*( b ) straight line*

*( c ) parabola*

*( d ) some other curve*

*25) The unit of Peltier coefficient is*

*( a ) J / C*

*( b ) J / A*

*( c ) J / V*

*( d ) None of these*

*26 ) The unit of Thomson’s coefficient is*

*( a ) J / C*

*( b ) J / A*

*( c ) J / V*

*( d ) None of these*

*27) Which is a characteristic temperature of thermocouple ?*

*( a ) cold junction temperature*

*( b ) hot junction temperature*

*( c ) inverse temperature*

*( d ) neutral temperature*

*28 ) During electroplating, 1.5 g of silver is deposited in 25 min. The ammeter connected in*

*series reads 1 A. Approximately by what percentage is the ammeter reading incorrect?*

*( a ) 10 % less than correct value*

*( b ) 11 % more than correct value*

*( c ) 13 % less than correct value*

*( d ) 12 % more than correct value*

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