## Saturday, 12 November 2016

### Chapter 11 Heat and thermodynamics

Heat and thermodynamics is last chapter of first year Physics book.This chapter holds quite an importance in board's exam.

#### Heat and thermodynamics MCQs

1.            The Avogadro number represents the number of atoms
in
(a)        1 kg of a substance          (b) unit volume of a substance
(c) 1 mole of a substance        (d) total amount of a substance

2.            Molecules of a mono atomic gas possess
(a)        rotational motion   (b) vibrational motion
(c) translational motion          (d) all of these

3.            A closed system is one in which
(a)        the energy of the system remains constant
(b)        the mass of the system remains the same
(c)        both mass and energy of the system remain the same
(d)       nether mass nor energy remain the same

4.            In a thermodynamical process the change in internal energy depends upon (a) the initial state only
(b)  the final state only
(c)  the path followed by the change
(d)  the initial and the final state

5.            The equation PV = constant holds in
(a)        isothermal process            (b) isochoric process
(c) adiabatic process              (d) all of these

6.            In a Carnot engine, the final temperature of the working substance is
(a)        greater than its initial temperature
(b)        smaller than its initial temperature
(c)        equal to its initial temperature
(d)       zero

7.            The working substance of a Carnot engine is
(a)        source                               (b) sink
(c) petrol                               (d) ideal gas

8.            Upon decreasing the temperature of the sink, the efficiency of the Carnot engine
(a)        decreases                         (b) does not change
(c) increases                         (d) none of these

9.            When the temperature of source and the sink become equal the change in entropy of a Carnot engine becomes
(a)        zero                                   (b) minimum
(c) maximum                         (d) negative

10.         All real heat engines are less efficient than a Carnot engine due to
(a)        working substance
(b)        temperature of the reservoirs
(c)        friction and heat losses
(d)       all of these

11.         The unit of thermodynamic temperature is
(a)        K                                       (b) OF
(c) OC                                    (d) none of these

13.         Human metabolism provides a good example of
(a)        mass conservation
(b)        energy conservation
(c)        entropy conservation
(d)       none of these

14.         The increase in thermal pollution of environments means
(a)        a decrease in entropy
(b)        an increase in entropy
(c)        constant entropy
(d)       none of these

15.         Upon shifting a simple pendulum from Karachi to Mount
Everest, its natural frequency
(a)        increases                          (b) decreases
(c) remains the same            (d) none of these

16.         Under similar conditions of temperature and pressure, the velocity of sound will be maximum in
(a)        oxygen                             (b) hydrogen.
(c) nitrogen                          (d) carbon dioxide

17.         Presence of moisture in air
(a)        increases the velocity of sound
(b)        decreases the velocity of sound
(c)        has no effect on the speed of sound
(d)       none of these

18.         A string of length l fixed at both ends is plucked from its middle so that it vibrates in one loop. The
wavelength of the wave in this mode is
(a)        l/2                                     (b) l
(c) 2l                                     (d) l/4

19.         The ratio of the fundamental frequency  of a organ pipe open at both ends to an organ pipe closed at both ends is
(a)        2:1                                    (b) 1:2
(c) 1:1                                  (d) 3:1

20.         When a simple pendulum swings, which of the following quantities is not zero throughout the motion?
(a)        Acceleration            (b) Speed
(c) Weight                             (d) Momentum

21.         A string with one end fixed is being whirled from the other free end so that it vibrates with the fundamental frequency of 20 Hz. Its next harmonic has  a frequency equal to
(a)        40 Hz                      (b) 60 Hz
(c) 10 Hz                               (d) neither of these

22.         In an interference pattern
(a)        bright fringes are wider than dark fringes
(b)        dark fringes are wider than the bright fringes
(c)        both dark and bright fringes are of equal width
(d)       none of these

23.         In a diffraction pattern, the fringes are
(a)        equally spaced
(b)        wider near the object and narrower away from it
(c)        narrower near the object and wider away from it
(d)       none of these

24.         The Celsius and Fahrenheit scales have the same reading at
(a)        40o                                    (b) 140o
(c) 40o                               (d) 140o

25.         Absolute zero is considered to be the temperature at which
(a)        all gases become liquid
(b)        all liquids become solid
(c)        water freezes
(d)       molecular motion in gases ceases

26.         Which of the followings do not have the same units?
(a)        Mechanical energy
(b)        Kinetic energy
(c)        Heat energy

(d)       Power