Sri Lanka Engineering Service Exam flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Darcy's law

Seepage velocity through soil is proportional to hydraulic gradient: q = k·i·A, where k is permeability and i is head loss per unit length.

Rational method

Peak storm runoff Q = C·i·A/360 with Q in m³/s, i in mm/h and A in hectares; C is the runoff coefficient and i the design rainfall intensity.

Modified Proctor test

Laboratory compaction test using a 4.5 kg hammer dropped 450 mm in five layers; gives maximum dry density and optimum moisture content for pavement subgrade.

Manning's equation

Open-channel velocity v = (1/n)·R^(2/3)·S^(1/2), where n is roughness, R hydraulic radius and S bed slope; used for sewer and drain design.

BOD₅

Biochemical oxygen demand measured over five days at 20 °C; indicates biodegradable organic strength of wastewater and sizes biological treatment units.

Rise and fall method

Levelling reduction where rise = previous staff − current staff and fall = current staff − previous staff; arithmetic check: Σrise − Σfall = last RL − first RL.

Euler buckling load

Critical axial load for a slender column: Pcr = π²EI/(KL)², where K depends on end restraint: 0.5 fixed-fixed, 0.7 fixed-pinned, 1.0 pinned-pinned, 2.0 cantilever.

Lever arm

Distance between the compressive and tensile resultants in a reinforced concrete section; for singly reinforced beams z ≈ 0.95d, giving As = M/(0.87 fy z).

Balanced section

Reinforced concrete section in which concrete reaches ultimate strain simultaneously with steel yielding; further steel cannot increase moment capacity.

Slenderness ratio

Effective length divided by least radius of gyration (or by depth for columns); determines whether second-order buckling effects must be included in design.

Zero-force member

Truss member carrying no load: at a two-member joint with no external load, or a three-member joint where two members are collinear, the third is zero.

Singly reinforced beam

Concrete beam with tension steel only; design moment resisted by concrete compression block and steel tension couple, valid while section is under-reinforced.

Per-unit system

Normalisation of power-system quantities to base values: Zpu = Zactual/Zbase with Zbase = Vbase²/Sbase; simplifies transformer and fault calculations.

Synchronous speed

Speed of the rotating magnetic field in an AC machine: Ns = 120f/P rpm, where f is supply frequency in Hz and P the number of poles.

Slip

Fractional difference between synchronous speed and rotor speed of an induction motor: s = (Ns − Nr)/Ns, typically 2–5% at rated load.

Surge impedance

Characteristic impedance of a lossless line Zc = √(L/C), about 400 Ω for overhead lines and 40–60 Ω for cables; natural power equals V²/Zc.

Power factor correction

Capacitor kVAR needed = P(tanφ1 − tanφ2); raising power factor reduces line current and losses for the same real power delivered.

Thevenin's theorem

Any linear network can be replaced at a pair of terminals by a voltage source Vth equal to the open-circuit voltage in series with Rth = Vth/Isc.

Otto cycle efficiency

Ideal spark-ignition cycle efficiency η = 1 − 1/r^(γ−1), where r is compression ratio and γ the specific heat ratio, about 1.4 for air.

Carnot efficiency

Maximum possible efficiency between two reservoirs: η = 1 − Tc/Th with absolute temperatures; no real heat engine can exceed this value.

Rankine cycle

Ideal steam power cycle of pump, boiler, turbine and condenser; efficiency = net work out divided by heat added in the boiler.

Darcy–Weisbach equation

Pipe friction head loss hf = f·(L/D)·v²/2g, where f is the friction factor, L pipe length, D diameter and v mean velocity.

Hoop stress

Circumferential stress in a thin-walled cylinder under internal pressure: σh = pD/(2t); longitudinal stress is half this value, pD/(4t).

Refrigeration COP

Coefficient of performance = heat removed divided by work input; for a Carnot refrigerator COP = Tc/(Th − Tc) using absolute temperatures.

Concrete characteristic strength

Cube strength below which no more than 5% of test results are expected to fall; the basis of 28-day acceptance criteria in BS EN 206.

Slump test

Workability test on fresh concrete using a standard cone; slump classes S1 to S4 range from 10–40 mm to 160–210 mm according to BS EN 12350-2.

Permit to work

Written authorisation required before confined-space entry, hot work or deep excavation; it records hazards, isolations, controls and the authorised persons.

First-angle projection

Orthographic drawing convention in which the object is placed between observer and plane, so the plan appears below the elevation; standard in Sri Lanka.

Alligation rule

Method for mixing two components of different value: ratio of quantities = (mean − cheaper) : (dearer − mean), used in mixture and ratio problems.

Work-rate formula

If A alone takes a days and B alone b days, together they take ab/(a + b) days, because their combined rate is 1/a + 1/b per day.

Successive percentage change

Two successive changes of a% and b% give a net change of a + b + ab/100 percent; a 20% rise then 10% fall yields a net 8% rise.

Sri Lanka independence

Ceylon became independent on 4 February 1948; it became a republic on 22 May 1972 and adopted its current constitution in 1978.