GCE A/L Engineering Technology flashcards

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

First-angle projection

Orthographic method in which the object sits between observer and plane, so the top view is drawn below the front view and the left view on the right.

Representative fraction

Ratio of drawing length to actual length, written as 1:50 or 1:100. A 6 m wall at 1:50 is drawn 120 mm long.

Young's modulus

Slope of the elastic part of the stress-strain curve, E = stress/strain. Mild steel is about 200 GPa and aluminium about 70 GPa.

Tempering

Reheating quenched steel to a temperature below the critical range to reduce brittleness and restore toughness while keeping most of the hardness.

Parallel-axis theorem

Second moment of area about any axis equals that about the centroidal parallel axis plus area times the square of the distance between them.

Bending equation

sigma/y = M/I = E/R relates bending stress, distance from neutral axis, bending moment, second moment of area and radius of curvature.

Kirchhoff's voltage law

Around any closed loop of a circuit the algebraic sum of emfs and potential differences is zero, expressing conservation of energy.

Transformer turns ratio

Secondary voltage divided by primary voltage equals secondary turns divided by primary turns; current ratio is the inverse for an ideal transformer.

Carnot efficiency

Maximum possible efficiency between two reservoirs, 1 minus cold absolute temperature divided by hot absolute temperature. No real engine exceeds it.

Latent heat of steam

Heat needed to change water at saturation temperature into dry saturated steam without raising temperature, about 2257 kJ/kg at atmospheric pressure.

Cutting speed

Surface speed of the workpiece or tool, V = pi times diameter times revolutions per minute divided by 1000, giving metres per minute.

Hole basis system

Limits and fits system where the hole size is fixed as H and the shaft letter sets the fit: a to h clearance, p to zc interference.

Vernier least count

Difference between one main scale division and one vernier division. With 50 vernier divisions spanning 49 mm the least count is 0.02 mm.

Accuracy versus precision

Accuracy is how close a reading is to the true value; precision is how closely repeated readings agree with each other.

Slump test

Workability test in which fresh concrete in a standard cone is allowed to settle; the drop in height indicates consistency.

Height of instrument

Reduced level of the benchmark plus the backsight reading. Subtracting a staff reading from it gives the reduced level of that point.

Object snap

CAD setting that locks the cursor to exact geometric points such as endpoints, midpoints, centres and intersections, ensuring accurate construction.

Paper space viewport

Layout area holding the title block and a window onto model-space geometry, set to a plot scale such as 1:10.

Critical path

Longest sequence of dependent activities through a project network, having zero float and therefore setting the shortest possible completion time.

Bill of materials

Itemised list of every part in an assembly with quantity, material, size and drawing reference, used for costing and procurement.

Hierarchy of control

Order of risk control: eliminate, substitute, engineer controls, administrative controls, then personal protective equipment as the last defence.

Permit to work

Formal written authorisation for high-risk tasks, recording isolation, precautions, time limits and the person in charge before work starts.

Geometric tolerance symbol

Frame showing characteristic such as flatness or position, the tolerance zone value, and the datum references that locate the feature.

Surface roughness Ra

Arithmetic mean deviation of the surface profile from its mean line, quoted in micrometres; 3.2 micrometres is typical turned work.

Poka-yoke

Error-proofing device or method that prevents a mistake being made or makes it immediately obvious, such as a locating pin.

Go/no-go gauge

Limit gauge pair where the go gauge must enter the part and the no-go gauge must not, checking maximum and minimum material conditions.

Betz limit

Maximum fraction of wind stream power any turbine can extract, 16/27 or about 59 percent, from momentum theory.

Round-trip efficiency

Ratio of energy recovered from storage to energy put in, always below 100 percent because of losses in charging, holding and discharging.

Hysteresis

Difference between instrument readings taken with increasing and decreasing input over the same range, caused by friction or elastic effects.

Wheatstone bridge

Four-arm resistance network that balances when the ratio of arms is equal, giving zero galvanometer current and allowing unknown resistance measurement.

Simply supported beam moment

Maximum bending moment is load times span divided by four for a central point load, and load per metre times span squared over eight for uniform load.