Transmission of Heat, Electrostatics
 
 1.    The coefficient of thermal conductivity of a metal depends on
 1)    Temperature difference between two sides
 2)    Thickness of metal plate
 3)    Area of the plate
 4)    Nature of the material
  
 2.    Heat is transmitted from higher to lower temperature through actual motion of the molecules in
     1) Conduction    
     2) Convection    
     3) Radiation    
     4) All of these
  
 3.    A piece of ice placed in a room
     1) Does not rate
     2) Radiates less but absorbs more
     3) Radiates more than it receives    4) Radiates as much as it receives
 4.    A red-glass piece is heated until it glows in dark. The colour of the glow will be
     1) Red    2) Orange    
     3) Green    4) Violet
  
 5.    A metal piece is heated upto T K. The temperature of the surroundings is t K. The heat radiated to the surroundings due to radiation is proportional to
     1) (T – t)4    2) T4 – t4    
     3) (T – t)1/4    4) T2 – t2
  
 6.    A sphere, a cube and a thin circular plate all made of the same material and having the same mass are initially heated to a temperature of 200°C. Which of these objects will cool slowest, when left in air at room temperature?
     1) The sphere    2) The cube    
     3) The circular plate        4) All will cool at the same rate
  
 7.    Absorptive power of a white body is
     1) 1        2) 0       3) 1        4) ¥  
  
 8.    Rods of different radii r and length l made of the same material are used to connect two sources of heat at two different temperatures. Which one will conduct maximum heat?
     1) r = 1 cm; l = 1 m
     2) r = 2 cm; l = 2 m
     3) r = 1 cm; l = 0.5 m
     4) r = 2 cm, l = 0.5 m
  
 9.    Two cylindrical conductors A and B of same material have their diameters in the ratio 1:2 and lengths in the ratio 2:1. If the temperature difference between their ends is same, then the ratio of the rate of heats conducted by A and B is
     1) 1 : 8    2) 1 : 4
     3) 1 : 2    4) 4 : 1
  
 10.    The colour of a star is a measure of its
     1) Age    2) Temperature    3) Size    
     4) Distance from the earth
  
 11.    24000 calories of heat flows across a silver cube of side 4 cm in one minute when its opposite faces are at 0°C and 100°C respectively. The coefficient of thermal conductivity of silver is
     1) 1 cal/cm/s/°C
     2) 2 cal/cm/s/°C
     3) 3 cal/cm/s/°C
     4) 1.5 cal/cm/s/°C
  
 12.    The outside of a beaker containing dry ice at 0°C is maintained at 40°C. The area of the glass in contact with ice is 250 cm2 and the thickness of glass wall of the beaker is 1.6 mm. If K of glass 0.0016 cgs units, then the rate at which ice starts melting is
     1) 1 g/sec    2) 1.75 g/sec    3) 1.5 g/sec    4) 1.25 g/sec
  
 13.    A compound slab is made with two different materials A and B with coefficients of thermal conductivities in the ratio 1:2 and the thickness in the ratio 2 : 1. If the free face of A is at 100°C and that of B is at 25°C, then the temperature of the interface is
     1) 20°C    2) 40°C
     3) 60° C    4) 90° C
  
 14.    What temperature gradient must exist in an aluminium rod in order to transmit 8 cal/s per square centimeter of cross-section down the rod? K for aluminium is 0.5 cal/s/cm/°C.
     1) 16° C/m    
     2) 15° C/m    
     3) 32° C/m    
     4) 30° C/m
  
 15.    A tungsten filament lamp of power 625 W is at 2227°C. The emissivity of the filament is 0.16. If s = 6 ´ 10–8 Wm–2 K–4. The surface area of the filament is
     1) 16.67 ´ 10–2 m2
     2) 14.67 ´ 10–4 m2
     3) 16.67 ´ 10–4 m2
     4) 14.67 ´ 10–2 m2
  
 16.    The radiant power of a furnace of surface area of 0.6 m2 is 36 kW. The temperature of the furnace is (s = 6 ´ 10–8 W m–2 k–4)
     1) 250 K    2) 500 K    
     3) 750 K    4) 1000 K
  
 17.    The rate of radiation from a block body at 0°C is E. The rate of radiation from this block body at 273°C is
     1) 16 E    2) 32 E    
     3) 8 E    4) 28 E
  
 18.    Hot water, at 80°C cools to 70°C is in 5 minutes. If the room temperature is 30°C in what time will it cool from 60°C to 50°C
     1) 6 minutes    2) 7 minutes    3) 9 minutes    4) 10 minutes
  
 19.    A body which has a surface area of 5.00 m2 and a temperature of 727°C radiates 3 ´ 1013 ergs each minute. If Stefan's constant s = 5.67 ´ 10–8 watt/m2–K4, then the emissivity of the body is
     1) 1.76    2) 0.176
     3) 17.6    4) 0.0176
  
 20.    [A]: Radiation is the speediest
        mode of heat transfer.
 [R]:Radiation can be transmitted
       in vacuum even in curved    
       path.
 1)    Both A and R are true and R is
     correct explanation for A
 2)    Both A and R are true and R is
     not correct explanation for A
 3)    A is true but R is false    
 4)    A is false but R is true  
  
 21.    A soap bubble is charged to a potential of 8V. Its radius is then doubled. The potential of the bubble now will be
     1) 16 V    2) 8 V        3) 4 V    4) 2 V
  
 22.    Two conducting spheres of radii r1 and r2 are equally charged. The ratio of their potentials is
     1)      2)     
     3)     4)
  
 23.    Two identical charges each are at a distance r apart. If the distance between them is to be halved, the work to be done is
     
     1)      2)       
     
     3)       4)
  
 24.    Following figure shows three points A, B and C in an electric field. If VA, VB and VC are the potential at these points, then
         1) VA = VB> VC
     2) VA < VC< VB
     3) VA = VB< VC
     4) VA > VC> VB
  
 25.    The capacitance of a parallel plate condenser does not depend on the
     1) Area of the plates        2) Medium between the plates
     3) Distance between the plates    4) Metal of the plates
  
 26.    A parallel plate condenser with oil between the plates (dielectric constant of oil = 2) has a capacitance C. If the oil is removed, the capacitance of the capacitor becomes
     1) Ö2 C     2) 2C
     3) C / Ö2     4) C / 2
  
 27.    A parallel plate condenser with a dielectric of dielectric constant K between the plates has a capacity C and is charged to a potential V volts. The dielectric slab is slowly removed from between the plates and then reinserted. The net work done by the system in this process is    
 
     1)     2) CV2(K – 1)/K 3) (K – 1) CV2      4) zero
  
 28.    A battery is used to charge a parallel plate capacitor till the potential difference between the plates becomes equal to the electromotive force of the battery. The ratio of the energy stored in the capacitor and the work done by the battery will be    
     1) 1       2) 2    3) 1/4     4) 1/2
  
 29.    Two point charges +25 C and – 6 C are 15.5 cm apart. The point between them at which the potential is zero is
     1) 10.5 cm from – 6 C
     2) 12.5 cm from + 25 C    
     3) 12 cm from – 6 C
     4) 11.5 cm from +25C
  
 30.    An electric field  is existing in a region. The potential at the origin (0, 0) is 0. Then the potential at P(2m, 3m)  is
     1) 180 V    2) 220 V
     3) 260 V    4) 200 V
  
 31.    Two plates of a parallel capacitor are at potentials 200V and – 200V. If the distance between plates is 4cm then find electric field at a distance 2cm from one plate in between plates.
     1) 102 V/m    
     2) 106 V/m    
     3) 103 V/m    
     4) 104 V/m
  
 32.    A bullet of mass 2 g is moving with a speed of 10 ms–1. If the bullet has a charge of 2 mC, through what potential must it be accelerated, starting from rest to acquire the same speed ?    
     1) 50 kV    2) 40 kV    
     3) 30 kV    4) 45 kV
  
 33.    A liquid drop of electric energy 16J is split into 8 small drops of same size. Then the electric energy of each drop is
     1) 0.2 J    2) 0.3 J
     3) 0.4 J    4) 0.5 J
  
 34.     Match the following: N identical charge droplets combines into a single drop. The potential capacity energy and surface charge density of bigger drop are V, C, U, s and each droplet one v, c, u, and s' respectively
     a) V / v     e) N1/3
     b) C / c    f)  N5/3
     c) U / u    g) N4/3
     d) s / s'     h) N2/3
     1) a – h , b – e , c – f , d – g     2) a – g , b – e , c – f , d – h
     3) a – g , b – f , c – e , d – h     4) a – g , b – f , c – h , d – e
  
 35.    Out of the following two statements
 [A]: As we move in the direction
     of the field potential goes on      
     decreasing  
 [B]: If a charged body is moved
     with in the field work must
     be done
 1)    A is correct and B is wrong
 2)    A is wrong and B is correct
 3)    Both A and B are correct
 4)    Both A and B are wrong
  
 36.    A cloud carrying a charge of 50 C is at a potential of 4200 V.  If it is discharged, then the amount of ice that can melt at 0° C is
     1) 7/8 kg    2) 3/8 kg
     3) 8/5 kg    4) 5/8 kg
  
 37.    The capacitance of a spherical condenser is 1.8 pF. It diameter is
     1) 3.24 cm    2) 1.28 cm    3) 2.24 cm    4) 16.2 cm
  
 38.    Three condensers of capacities 3 mF, 6mF, 12mF are connected in series with a battery, If the charge on 12mF condensers is 24mC, then the P.D. across the battery is  
     1) 12 V    2) 14 V    
     3) 16 V    4) 18 V
  
 39.    The equivalent capacitance of two condensers is 3 mF when connected in series and 16 mF when connected in parallel. The individual capacitances are
     1) 4 mF, 8 mF    
     2) 12 mF, 4 mF    
     3) 12 mF, 16 mF
     4) 4 mF, 16 mF
  
 40.    Two metal spheres of radii 10 cm and 17 cm are kept in contact.  Then the equivalent capacity of the combination is
     1) 3 ´ 10 –11 F    2) 2 ´ 10–11 F    3) 4 ´ 10–11 F    4) 2.5 ´ 10–11 F
  
 Key
 
 1)  4;    2)   2;    3)  2;    4)  3;    5)  2;    6)   1;    7)   2;    8)  4;    9)  1;    10)  2;    11) 1;    12) 4;    13) 2;     14) 1;    15) 3;    16) 4;    17) 1;     18) 3;    19) 2;    20) 3;    21) 3;     22) 4;    23) 1;    24) 2;    25) 4;     26) 4;    27) 4;    28) 4;    29) 2;     30) 3;    31) 4;    32) 1;    33) 4;     34) 1;    35) 1;    36) 4;    37) 1;     38) 2;    39) 2;    40) 1.