Environmental Physics Revision Exercise

ENVIRONMENTAL PHYSICS (REVISION EXERCISE 02)

To be submitted by 15th May (0700)

Question 01

(a) Define the term "angle of inclination" and "angle of declination" as used in specification of Earth's Magnetic Field at a point.

If the horizontal component of Earth's Magnetic Field at a location was found to be DE/VI while the angle of inclination was 59°F, find the magnitude of the field and the vertical component of the field at that location.

(b) Define an Earthquake

Distinguish between P and S waves which are radically different in velocities

Question 03

(a) What is the importance of ionosphere to radio communication?

(b) Explain why transmission of radio waves is better at night than during the day.

(d) Define Earthquake focus, Earthquake epicenter and state any (4) indications that may precede the occurrence of Earthquakes.

Question 04

(a) Explain two variations of Earth's Magnetic Field.

(b) State precautions taken by people living in a region with a high risk of occurrence of Earthquakes.

I. Solar wind
II. Magnetopause
III. Ionosphere

(d) Define the following terms:

Priority distance
Root waves

Question 05

(a) State two (2) ways by which seismic waves may be produced.

(b) What is seismic prospecting?

(c) The average velocity of P-waves through the Earth's soil space is 84m/s. If the average density of Earth's rock is 5.5×10² kg/m³ and the average bulk modulus of Earth's rock is given, calculate...

(d) Construction of dams often increases earthquake activity. Justify this statement.

(e) Explain why solar energy is considered to be renewable energy.

Question 06

(a) An old photovoltaic module of area 0.78m² has the following parameters:

I_sc = 5.2A, V_oc = 21.7V

V_mp = 15.6V, I_mp = 4.7A

recorded at irradiance of 1000Wm^-2

→ Calculate Fill Factor (FF)

→ Calculate efficiency of the Module

(b) Describe the workings of two types of wind turbine blades

(c) Explain how electricity can be generated from the wind and why tip speed ratio (TSR) is an extremely important factor in wind turbine design.

(d) State five (5) environmental benefits of geothermal energy.

Additional Questions

How is the magnetic field within atmosphere generated?

State two (8) ways by which seismic waves may be produced.

What is seismic prospecting?

Environmental Physics Revision Answers

Question 1: Earth's Magnetic Field

(a) Definitions and Calculations

Angle of inclination (dip angle): The vertical angle between Earth's magnetic field lines and the horizontal plane, ranging from 0° at the equator to 90° at the magnetic poles.

Angle of declination: The horizontal angle between true north (geographic north) and magnetic north, varying by location and time.

Given: Horizontal component (B_h) = DE/VI, Inclination (θ) = 59°
Total field magnitude: B = B_h/cosθ
Vertical component: B_v = B_h × tanθ

(b) Earthquakes and Seismic Waves

Earthquake: A sudden release of energy in Earth's lithosphere that creates seismic waves, typically caused by tectonic plate movements.

Characteristic	P-waves (Primary)	S-waves (Secondary)
Speed	5-8 km/s (faster)	3-5 km/s (slower)
Motion	Compressional (push-pull)	Transverse (side-to-side)
Medium	Travel through solids and liquids	Only through solids
Arrival	First to arrive	Second to arrive

Question 3: Ionosphere and Earthquakes

(a) Ionosphere Importance

The ionosphere (60-1,000 km altitude) reflects radio waves (especially HF bands) enabling long-distance communication via skywave propagation, critical for:

Shortwave radio broadcasting
Amateur radio communication
Over-the-horizon radar
Satellite communication signal propagation

(b) Day vs Night Radio Transmission

Daytime:

D-layer forms (50-90 km altitude)
Absorbs MF and HF radio waves
Limits transmission range

Nighttime:

D-layer disappears after sunset
E/F layers reflect signals farther
Allows long-distance skywave propagation

(c) Earthquake Causes

Tectonic activity: Plate boundary movements (transform, convergent, divergent)
Volcanic activity: Magma movement and eruptions
Human-induced: Reservoir-induced seismicity, mining, fracking
Fault reactivation: Stress release along pre-existing faults

(d) Earthquake Terminology

Focus (hypocenter): The subsurface point where earthquake rupture initiates (typically 5-700 km depth)

Epicenter: The surface projection directly above the focus

Precursors (4 examples):

Foreshocks (small preceding earthquakes)
Groundwater level changes
Unusual animal behavior
Increased radon gas emission

Question 4: Magnetic Field and Earthquake Safety

(a) Magnetic Field Variations

1. Secular Variation:

Slow changes in declination (0.1°-0.2° per year)
Caused by core dynamo changes
Complete polarity reversals every ~300,000 years

2. Diurnal Variation:

Daily fluctuations (25-50 nT amplitude)
Caused by solar wind interactions
Peak around local noon

(b) Earthquake Precautions

Structural: Earthquake-resistant building design (base isolation, shear walls)
Preparedness: Emergency kits (food, water, first aid)
Planning: Family evacuation plans and meeting points
Home safety: Securing heavy furniture and appliances
Education: Regular earthquake drills (Drop, Cover, Hold On)
Infrastructure: Gas shut-off valves and flexible utility connections

(c) Space Weather Terms

Solar Wind:

Stream of charged particles (plasma) from Sun's corona
Typical speed: 400 km/s (range 250-800 km/s)
Composition: 95% protons/electrons, 4% alpha particles

Magnetopause:

Boundary where solar wind pressure balances Earth's magnetic field
Typically 10-12 R_E (Earth radii) on sunward side
Extends into long magnetotail on night side (up to 1000 R_E)

Ionosphere:

Atmospheric layer (80-600 km) with ionized particles
Critical for radio propagation and GPS signal delay
Contains D, E, and F regions with different properties

Question 6: Renewable Energy Systems

(a) Photovoltaic Calculations

Given parameters for PV module:

Area (A) = 0.78 m²
Short-circuit current (I_sc) = 5.2 A
Open-circuit voltage (V_oc) = 21.7 V
Max power voltage (V_mp) = 15.6 V
Max power current (I_mp) = 4.7 A
Irradiance (G) = 1000 W/m²

Fill Factor (FF) Calculation:

FF = (V_mp × I_mp) / (V_oc × I_sc)
= (15.6 × 4.7) / (21.7 × 5.2)
= 73.32 / 112.84 ≈ 0.65 (65%)

Efficiency (η) Calculation:

P_max = V_mp × I_mp = 15.6 × 4.7 = 73.32 W
η = P_max / (A × G) = 73.32 / (0.78 × 1000)
= 73.32 / 780 = 0.094 → 9.4%

(b) Wind Turbine Types

Feature	HAWT (Horizontal Axis)	VAWT (Vertical Axis)
Orientation	Blades rotate perpendicular to wind	Blades rotate parallel to axis
Efficiency	Higher (40-50%)	Lower (30-40%)
Yaw Mechanism	Required to face wind	Not needed (omnidirectional)
Installation	Tower-mounted	Ground-level components

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