Cameroon CAP Vocational Trades flashcards

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

Ohm's law

Voltage equals current multiplied by resistance (U = R × I). Rearranged, current is voltage divided by resistance and resistance is voltage divided by current.

Three-phase power formula

For a balanced three-phase load, real power equals √3 × line voltage × line current × power factor. Power factor is the cosine of the phase angle between voltage and current.

Cutting speed formula

Cutting speed in metres per minute equals π × diameter in mm × spindle speed in rpm, divided by 1000. It is used to select the correct spindle speed for a drill or lathe tool.

Tapping drill size

For a metric thread, tapping drill diameter equals nominal diameter minus pitch. For M12 × 1.75 the tapping drill is 10.25 mm, giving about 75 percent thread engagement.

Concrete mix ratios

Common site volume ratios are 1:2:4 for a C20-class mix and 1:1.5:3 for a C25-class mix, cement to sand to aggregate. The water-cement ratio controls strength.

Filing a flat surface

Use the full length of the file with even pressure, cross-file then draw-file, and check flatness with a straightedge in two directions before the finishing pass.

Hacksaw blade selection

Use 18 to 24 teeth per inch for thick sections and 32 teeth per inch for thin tube. Keep at least three teeth engaged in the cut to avoid stripping the teeth.

Tapping procedure

Start the tap square to the hole using a tapping block, advance half a turn then back a quarter turn to break chips, and use cutting paste on steel.

Curing concrete

Keep concrete damp for at least seven days after placing. Curing allows cement hydration to continue, which develops strength and reduces surface cracking.

Micrometer reading

Read the barrel in millimetres, then add the thimble reading multiplied by 0.01 mm. Check the zero before use and close with the ratchet stop to avoid over-tightening.

Vernier caliper reading

Add the main scale reading to the coinciding vernier line multiplied by the least count, which is 0.02 mm for a fifty-division vernier. Close the jaws to check zero.

Torque wrench storage

Store a torque wrench at its lowest setting so the spring is not left compressed. Never use it to loosen fasteners, and keep it within its calibration date.

Grinding wheel ring test

Tap a new wheel lightly with a non-metallic object. A clear ring means it is sound; a dull thud means it is cracked and must be discarded, never mounted.

Hierarchy of control

Controls are applied in order: eliminate the hazard, substitute it, use engineering controls, then administrative controls, and finally personal protective equipment as the last resort.

Lockout and tagout

Isolate the energy source, apply a personal lock and tag, release stored energy, and prove the equipment is dead before starting work. Only the person who applied the lock removes it.

Fire classes and extinguishers

Class A solids use water, class B liquids use foam or carbon dioxide, class C gases use dry powder, and class D metals need special powder. Never use water on live electrical equipment.

First-angle projection

In first-angle projection the view is placed on the far side of the object from the observer. Third-angle projection places the view on the near side. Check the symbol in the title block.

Tolerance and limits

A dimension of 25 ±0.2 has limits of 24.8 and 25.2 mm, giving a total tolerance of 0.4 mm. The tolerance is the permitted variation from the nominal size.

Surface roughness Ra

Ra is the arithmetic mean roughness in micrometres. Typical values are 3.2 for general machining, 1.6 for fine machining and 0.8 for precision grinding.

Three-four-five rule

A triangle with sides in the ratio 3:4:5 has a right angle between the two shorter sides. It is used on site to set out a square corner.

Job handover note

A written handover records the date and time, the machine or site, work done, outstanding work, defects found, and the name and signature of the person handing over.

Refusing unsafe work

A worker may refuse an instruction that is unsafe. The refusal is reported through the chain of command and recorded in writing so the reason is documented.

Technical report structure

A technical report contains a title, objective, method, results, conclusion and recommendations, followed by the author's signature and the date. Headings make it easy to read.

Break-even quantity

Break-even quantity equals fixed costs divided by the difference between unit selling price and unit variable cost. At that quantity total revenue equals total cost.

Mark-up versus margin

Mark-up is profit divided by cost, while margin is profit divided by selling price. A 25 percent mark-up on cost equals a 20 percent margin on price.

Straight-line depreciation

Annual depreciation equals the purchase cost minus the residual value, divided by the useful life in years. It spreads the cost of equipment over the years it is used.

Cash flow versus profit

Profit is revenue minus costs over a period, while cash flow is money actually received and paid. A profitable job can still fail if the client pays late.

Price including tax

Multiply the price excluding tax by one plus the tax rate to get the price including tax. The tax collected is not business income and must be declared and paid.

Rule of three

If a quantity a costs c, then quantity b costs b × c ÷ a, provided the relationship is proportional. Cross-multiplication solves the same proportion.

Percentage change

Percentage change equals the new value minus the old value, divided by the old value, multiplied by 100. A negative result is a decrease.

Metric unit conversions

One metre equals 100 centimetres or 1000 millimetres. One square metre equals 10 000 square centimetres. One litre equals one cubic decimetre or 1000 cubic centimetres.

Mean, median and mode

The mean is the sum divided by the count, the median is the middle value of an ordered list, and the mode is the most frequent value. The median resists extreme values.