Download 5 marks - Sheffield Hallam University

SHEFFIELD HALLAM UNIVERSITY
SCHOOL OF ENVIRONMENT AND DEVELOPMENT
(+ ENGINEERING + SCIENCE)
Course : BSc ENVIRONMENTAL MANAGEMENT
Unit : PHYSICAL SCIENCE
Assessment : END OF UNIT TEST
Date : FRIDAY 18 MAY 2001
Time : 2.15 pm
Duration 1.5 hour
INSTRUCTIONS
1. Attempt ALL questions in Section A. Recommended time : 45 minutes.
2. Attempt TWO questions from Section B. Recommended time : 45
minutes.
3. The marks for all questions are indicated on the question.
A formulae sheet is attached for your use.
SECTION A
Answer ALL the questions in Section A
A1.
Write brief notes to describe the composition of the nucleus and explain
how isotopes occur.
(8 marks)
A2.
"The activity of a radionuclide decreases exponentially with time". Explain
this statement illustrating your answer with an appropriate graph and
indicate on your graph the half-life of the radio-active source.
(8 marks)
A3.
Describe the physiology of the ear and how it converts sound pressure
waves into electrical signals which are sent to the brain.
(8 marks)
A4
A current of 0.5 A passes through a 5-ohm resistor. Calculate the voltage
produced across the resistor and the power dissipated in it.
(5 marks)
A5.
Explain how
(a) a fuse, and
(b) a residual-current circuit breaker
are used to protect the users of electrical circuits. Against what hazards
does each device protect ?
(6 marks)
A6.
Explain with the aid of a suitable diagram how an air-conditioner works.
Why can the Coefficient of Performance of such a device be greater than
1 without infringing the First Law of Thermodynamics ?
(8 marks)
A7.
A piece of metal is dropped to the ground from a height of 20 m. Its
specific heat is 3.5 kJ kg-1 C-1 and the acceleration of gravity is 9.81 m s2. Making reasonable assumptions, calculate the speed it will have
reached immediately before hitting the ground and the amount by which
its temperature will rise on hitting the ground. How would the answers be
likely to be slightly different in practice ?
(7 marks)
SECTION B
Answer any TWO questions in Section B
B1.
Describe what happens when a charged particle passes through a
material.
(6 marks)
Draw diagrams to illustrate the differences between the absorption of
alpha and beta particles.
(9 marks)
The linear absorption coefficient of body tissue for a beam of gamma rays
is 7.0 m-1. Define the half-thickness of a material and use your definition
to calculate its value for tissue.
(10 marks)
[TOTAL 25 MARKS]
B2.
Describe the phenomenon of sound using appropriate graphs to define
the period and the wavelength.
(6 marks)
What is the relationship between period and frequency? Write down an
equation linking frequency, wavelength and velocity of a wave.
(7 marks)
The average ear can only detect sounds within a certain frequency range.
What are the limits of this range? Calculate the wavelengths
corresponding to these limits given that the speed of sound in air is
approximately 340 ms-1.
(12 marks)
[TOTAL 25 MARKS]
B3.
(a)
By reference to the First Law of Thermodynamics, explain why air
pumped into a bicycle tyre becomes hot as it is pumped.
(5 marks)
(b)
(i)
At a pressure of 1 bar and a temperature of 16 C, a
particular mass of gas occupies a volume of 8 litre. If it is compressed to a
pressure of 2 bar at the same temperature, what volume will it occupy?
(ii)
If it were then heated to 50 C at the same pressure of 2
bar, what would its final volume be ?
(9 marks)
(c)
During one cycle of operation of a particular Diesel engine, the
combustion of the fuel produces 25 kJ of energy. The power stroke
delivers 31 kJ and the work done in compression is 26 kJ.
(i)
Calculate the efficiency of the engine and the heat rejected during
the cycle.
(ii)
It is frequently argued that Diesel engines are more polluting than
petrol engines. Present one argument that they are more polluting and
one argument that they are less so.
(11 marks)
[TOTAL 25 MARKS]
B4.
(a)
Sketch a block diagram of a boiler-steam turbine-alternator plant
for electrical power generation. Indicate the main energy flows, including
heat losses. Why is it beneficial to allow the steam to expand to a
pressure lower than atmospheric and how is such an expansion achieved
in practice ?
(9 marks)
(b)
Explain, with the aid of a block diagram, how a combined-cycle
arrangement using a boiler and steam-turbine can add considerably to the
efficiency of the system of Part (a) as a power generator.
(8 marks)
(c)
Explain the operation of a dehumidifier for reducing dampness in
building interiors.
(8 marks)
[TOTAL 25 MARKS]
B5.
Explain the following points in as much detail as you are able in the
time allowed.
a)
Why alternating current, rather than direct current, is almost
universally used for electrical power supplies.
(7 marks)
b)
Why it is usual to generate electrical power at typically 11 kV,
transmit it through the National Grid at up to 400 kV and more
locally at 11 kV, but utilise it at 240-415 V.
(9 marks)
c)
How Kirchhoff's Current Law could be verified in the laboratory.
(9 marks)
[TOTAL 25 MARKS]
FORMULAE (NB Not all the formulae are required).
Radiation
A = Aoe-t
T1 
2
Ln(2)
λ
Noise
SPLnett = 10 Log (10 L1/10  10 L2 /10 )
Mechanics
Potential Energy
=
mgh
Kinetic energy
=
1 2
mv
2
Work
=
Force x distance moved
=
Pressure x volume change)
=
W + E
(Or
Thermodynamics
First Law
Specific Heat
Q
E = smT
General Gas Equation
PV = mRT
(R = 287 J kg-1 K-1)
Electrical
Ohm’s Law:
E = IR
Kirchhoff’s Current Law: At any junction in a circuit, the total current flowing in
must equal the total current flowing out.
Kirchhoff’s Voltage law:
Round any closed path in a circuit, the total e.m.f. of
the voltage sources in the path must equal the sum of the products of current
and voltage (“the IR drops”) for the resistors in the path.
Power = V x I ( = V2/R = I2R )