THE LUSAKA APEX MEDICAL UNIVERSITTY
FACULTY OF PRE – MEDICAL SCIENCES
DEPARTMENT OF PHYSICS
TEST ONE
INTRODUCTORY PHYSICS II (P192)
PREPARE BY MR. CHOLA
CANDIDATES DETAIL
NAME
R. Chola
COMP.NO
TG
LG
INSTRUCTION
ANSWER ALL
Data
Specific heat capacity of water = 4200 J kg-1 K-1.
Specific heat capacity of iron at 100 °C = 220 J kg-1 K-1.
Latent heat of vaporisation of water = 2260 kJ kg-1.
QUESTION ONE
a) What is meant by the Temperature of an object?
b) State Charles and Boyle’s law
Charles law; The volume and absolute temperature (K) of a gas are directly related at
constant mass & pressure
Boyle law; The volume and absolute temperature (K) of a gas are directly related at
constant mass & pressure
c) Distinguish between heat engines and refrigeration with regards to second law of
thermal dynamics
In a heat engine heat moves from a region of high temperature to region of low
temperature, in a fridge, heat moves from a cold region to a hot region
d) Derive the ideal gas equation
A general derivation of the ideal gas equation with the help of gas laws is
discussed below:
Boyle’s Law states that for a fixed number of moles of a gas the volume of a gas
varies inversely with its pressure at a constant temperature
V ∝ 1/P ————— (1)
Where,
V= volume
P = pressure
According to the Charles’ Law, at constant pressure, the volume of a fixed mass
of a gas is directly proportional to its absolute temperature.
V ∝ T — ———————- (2)
Where, T= temperature
According to the Avogadro’s Law, at same temperature and pressure, an equal
volume of gases contain an equal number of molecules.
V ∝ n ———————— (3)
Where, n = number of moles of gases
From equation (1), (2) and (3), we can deduce that,
V ∝ nT/P
⇒ V = RnT/P
Pv=nRT
Where R is known as a universal gas constant. The above equation is commonly
known as an ideal gas equation. Value of R can be calculated at STP (standard
temperature pressure) for one mol of gas as:
Volume at STP = 22.710981 L/mol
Pressure at STP = 1 bar = 105 Pa
Temperature at STP = 273.15
R = 22.710981 × 105273.15 = 8.314JK−1mol−1
e) Compare the energy needed to raise the temperature of 1kg of water from 20°C to
100°C and the energy needed to boil 1 kg of water at 100°C.
ANSWER
Energy required to heat the water = mCθ = 1  4200  80 = 336 kJ
Energy required to boil the water = mL = 1  2260 kJ = 2260kJ.
So it takes nearly 7 times as much energy to boil the water as to heat it up.
QUESTION TWO
An unknown metal decreases in length from 9.36m to 9.22 m. This change happened when
the temperature fell from 36.2°C to -3.2o C. what is the coefficient of linear expansion?
380*10-6
QUESTION THREE
Mark the statements you consider TRUE [4 MARKS] SUBTRACT 1 FOR WRONG
ANSWER
1. Entropy is a scalar quantity. TRUE
2. Heat cannot flow from colder objects to hotter ones. FALSE
3. The first law of thermodynamics is a special case of the second law of
thermodynamics. FALSE
4. Gases are more disordered systems than solids. TRUE
A copper bar, of length 10cm width 9mm and thickness 3mm has a thermal
conductivity 400 Wm-1K-1. This is connected between two objects whose
temperatures differ by 60oC. Calculate the rate of heat flowing through the bar.
6.48 Wm-1K-1
QUESTION FOUR
A refrigerator with C.O.P. = 4.7, extracts heat from the inside at a rate of 250 J per cycle. (a)
How much work per cycle is required to operate the refrigerator? (b) How much heat per
cycle is discharged into the room?
53 J, 303 J
53.2 + 250