AREA 3 Tambong

Ohm's law

States that the voltage or potential difference between two points is directly proportional to the current or electricity passing through the resistance and directly proportional to the resistance of the circuit.

2

Based on the 2009 Philippine Electrical Code, what is the minimum conductor size in mm2 for a voltage rating of 0-2,000 volts when using copper wire?

14

(AWG 14 has 2.08 mm2 conductor size, AWG 16 should not be used in houses. Except for the drop wire, the common household wires are AWG nos. 10, 12 & 14.)

A farmhouse requires a minimum conductor size of 2 mm2 which is equivalent to AWG ____.

AWG 8

Which electrical wire in the list below has the biggest cross-sectional area?

THHN

Which type of electrical wire has a maximum operating temperature of 90 oC?

8

Based on the Phil. Electrical Code, what is the minimum conductor size in mm2 for a voltage rating of 2,001-8,000 volts when using copper, aluminum or copper-clad aluminum wire?

IR

If V is voltage, I is current and P is power, according to Ohm's law, V is equal to _____.

Both DC and AC

Ohm's law is applicable to _____.

Inductance

Ohm's law applies to both AC and DC circuits as long as mutual _________ of the circuit is considered.

1.72 x 10^8

The resistivity of annealed copper in ohm meters at 20oC.

Resistivity

The resistance of a certain length of wire can be obtained by multiplying its ________ with its length and dividing the resulting product by the cross-sectional area of the wire.

700

A farmstead has its farthest load located 350 linear meters from a single phase power source. What length of the wire in meters should be used in the voltage loss computation?

Drop

In connecting electricity from a post to a farmhouse, a ______ wire is needed.

AWG 6

The minimum wire size for a farmhouse drop wire.

220 Vac

A solar powered slaughterhouse uses electrical stunning gun to make the animals insensible to pain before the slaughter. What should be the voltage of the stunning gun?

500

Based on PAES 419:2000, the recommended lighting intensity in lux (lumen/m2 ) for fruit and vegetable processing plant are: 100 for outside the building, 200 for general indoor locations, and ___ for working tables.

100

(since a 100-watt daylight-color LED bulb brightens by about 1,600 lumens)

A poultry layer area requires a brightness of 1,600 lumens. What is the wattage of a daylightcolor LED bulb that shall be used?

220 volts

Applying the formula V=IR in the third quadrant of the formula wheel, V = IxR

= (1 A) x (220 ohms)

= 220 volts

What is the voltage needed to light a 1-ampere LED bulb having a resistance of 220 ohms?

1 amp

Applying the formula I=P/V in the fourth quadrant of the formula wheel,

I = P/V

= (10 x 22 w) / (220 v)

= 1 Amp

How many amperes will pass through a circuit having ten 22-watt LED bulbs if the source is 220 volts?

0.02 kwh/kg

Solution:

Ec = PcTo / Wi

= 15 kw (2 h) / 1,500 kg

= 0.02 kwh/kg

What is the electrical energy consumption of a 15-kw vermin cast production shredder plugged in a 220-volt source if it requires 2 hours to shred 1.5 tonnes of farm waste?

3.27x10-3 ohms

Solution:

Determining the cross-sectional are of the wire in square meters,

A = 3.1416 x (Diameter)2 / 4

= 3.1416 x (2.588 mm x 1 m/1000 mm)2 / 4

= 5.26 x 10-6 m2

Determining the resistance of AWG 10 solid annealed copper wire per linear meter,

R = Resistivity x Length / Cross-sectional area

= (1.72 x 10-8 ohm-m) x (1 m) / (5.26 x 10-6 m2 )

= 3.27 x 10-3 ohms

Solid annealed copper has a resistivity of 1.72 x 10-8 ohm-meter at 20 oC. What is the resistance in ohm-meter per linear meter of AWG 10 solid annealed copper wire having a diameter of 2.588 mm?

0.03 A

A 240-volt industrial incubator uses a pair of 25-meter 7-strand AWG 10 copper wire having a resistance of 3.87x10-3 ohm per linear meter at 65 oC. The heating load of the incubator is composed of twelve 100-watt heating coils. What is the expected current in the main wire?

Solar Home System

In off-grid farmhouse electrification, which one has the lowest operation and maintenance cost?

Diesel generator

Which one has the highest operation and maintenance cost?

Grid extension

In off-grid barangay electrification located 3 kilometers from the electricity grid, which one is recommended?

Solar Home System

Which electricity source has no greenhouse gas emission?

Diesel generator

Which electricity source has the highest greenhouse gas emission?

Inverter

To minimize power loss, which equipment is needed to transform DC electricity from a centralized solar power plant into AC electricity before transmitting it to distributed 220-volt farmstead electrical devices?

Minihydro

(Under the Philippine classification, minihydro is over 100 kw up to 10 mw)

A 950-kw cassava flour processing plant is to be powered using hydro. Which electricity source will you use recommend?

Microhydro

(Picohydro is up to 5 kw only while mini and small hydros are oversized)

A 3 hectare hillside farm is to be energized. It is 20 meters below a river having a dependable summer discharge of 50 liters/second. Which electricity source will you use recommend?

Picohydro

(since power requirement is less than 5 kw, picohydro is recommended)

The 1-kw lighting of a farmstead is to be energized using hydropower. It is 10 meters below a creek having a dependable summer discharge of 5 liters/second. Which hydropower will you recommend for development?

16

Solution:

Using the rule of thumb formula, this takes efficiency into consideration.

P = 0.1 AV3 , P is power output in watts, A is rotor area in m2 , V is windspeed in m/s

= 0.1 [3.14 x (2.5 m)2 /4] [3.2 m/s]3

= 16.08 watts

An 8-bladed horizontal axis windmill with 12-meter tall tower has 2.5-m diameter rotor. Estimate the power output in watts using the rule of thumb formula. Average windspeed in the site is 3.2 m/s.

425

Solution:

No. of households = (Power Output - Power Loss) / Average household consumption

= (500 kw - 0.15 (500 kw) / 1 kw

= 425 households

How many households can be powered by a minihydro having a power generation output of 500 kw if an average household consumes 1 kw and power loss is 15%?

4

Solution:

No. of batteries in series = System Voltage / Battery nominal voltage

= 48 volts / 12 volts

= 4 batteries in series

A battery bank of a centralized solar power generator needs to store energy in a 48-volt DC system to power a cassava processing plant. If each battery is 12 volts, how many batteries are there in series?

15

Solution:

No. of batteries in series = System Voltage / Battery nominal voltage

= 48 volts / 12 volts

= 4 batteries in series

No. of batteries in parallel = Total number of batteries / No. of batteries in series

= 60 total batteries / 4 batteries in series

= 15 batteries in parallel

An off-grid tomato processing plant has 48-volt output battery bank composed of 60 units of 12-volt automotive batteries. How many batteries are there in parallel?

589

Solution:

P = 9.81 QHE, P in kw, Q in m3 /s, H in m, E in ratio

= 9.81 (1 m3 /s) (100 m) (0.6)

= 588.6 kw

How kilowatts can be generated from a waterfall having a discharge of 1 m3 /s, reliable head of 100 meters during summers and system efficiency of 60%?

1.32

Solution:

Use the minimum discharge, include depth of turbine water inlet to the head.

P = 9.81 QHE, P in kw, Q in m3 /s, H in m, E in ratio

= 9.81 (1.8 m3 /s) (95 m + 30 m) (0.6)

= 1,324 kw x 1 MW/1,000 kw

= 1.32 MW

A hydropower resource with water outlet 95 meters high from ground surface has fluctuating discharge of 1.8 m3 /s during summers and 3.5 m3 /s during rainy months. How many megawatts can be generated at the powerhouse placed below the ground surface with the turbine water inlet 30 meters below ground level? Assume a reliable system efficiency of 60%.

29

Solution:

P = No. of modules x Power rating x Sunlight hours x Inversion eff x Match eff x Trans. eff

= 100 x 0.075 kw x 5 hours 0.85 x 0.95 x 0.95

= 28.77 kwh

A centralized solar power plant with DC to AC inverter is used to electrify a farmstead using 75 watt-peak solar modules of the same brand. How many kilowatts-hours of energy in an average day of 5 hours sensible sunlight can be generated by 100 units of solar modules if inversion efficiency is 85%, module matching efficiency is 95% and transmission efficiency from modules to centralized battery bank is 95%?

Microcontroller

The board used in Arduino open-source electronics platform based on easy-to-use hardware and software which is able to read inputs like light on a sensor, temperature reading, a finger on a button, or a Twitter message and can turn these inputs into outputs like activating a motor, turning on an LED, turning on a solenoid valve, or publishing something online.

Solenoid valve

An Arduino microcontroller is used to activate mist sprinkler system for 10 minutes every time the greenhouse temperature rises above a certain level. What device is best turned on by the microcontroller to start the mist sprinklers?

Sketch

The name given to Arduino code files which serve as instructions to the microcontroller.

Bypass diode

Part of solar module needed such that solar charging is continuous at slower rate when partially shaded by trees.

Blocking diode

A diode needed as protection against lightning in solar installations.

Ground

The common pin, made as the pair to other pins, in integrated circuits (ICs).

Timer

An integrated circuit (IC) included as an important part of electronic instrumentation for gathering speed and discharge real-time data.

LM 333

Which one is an integrated circuit (IC) used in instrumentation and control?

5, 7 and 9 Vdc

What voltage is appropriate in remote instrumentation?

Radio frequency

Data transmission to a remote, unelectrified and line-of-sight point is best done through ___.

Automatic transfer switch

In automatic control of irrigation dam gates, what switch is useful in the instrumentation?

Pressure switch

Switch for automatic pump motor control of sealed water tanks in drip irrigation systems.

1%

Under PAES 418:2002, washing of tomato is done by using ____% chlorox solution applied by dipping, spraying or wiping with a damp cloth then drying the fruit before packing.

4.27

Based on PAES 419:2000, the recommended optimum stack height in meters for storage of both paddy and rice grains.

PAES 422-2:2012

What standard shall be followed in constructing large-scale poultry dressing/slaughtering plants?

4.57

Based on PAES 419:2000, the recommended optimum stack height for storage of wheat, barley and maize grains.

14

PAES 419:2000 requires that food grains stored in a warehouse for bagged storage are in the range of 12 to ____ % moisture content prior to storing.

PNS/BAFS 290:2019

The Philippine standard for grading and classification of paddy and milled rice grains.

PNS 42:2019

The Philippine standard for code of practice and postproduction of organic milled rice.

PNS 162:2015

The Philippine standard for Maximum Residue Limits (MRLs) of pesticide residues in rice.

PNS 194:2017

The Philippine general standard for contaminants and toxins in food and feed.

Product recall

Industrial bottling of virgin coconut oil prints a batch number. What is the main purpose of this batch number?

Conveyor

Which one is not a part of a vertical feed mixer?

Good

A feed mixer tested to have mixing coefficient of variation of 10-15% is rated as _____.

80%

As a standard, stripping efficiency of the mechanized stripping machine shall be at least

22

Solution:

MCdb = 100% x (Wet weight - Dry weight) / Dry weight

= 100% x (100 gm - 82 gm) / 82 gm

= 21.95%

What is the percent moisture content in dry basis of a rice sample having 100 grams and 82 grams wet and dry weights?

18

Solution:

MCwb = 100% x (Wet weight - Dry weight) / Wet weight

= 100% x (100 gm - 82 gm) / 100 gm

= 18%

What is the percent moisture content in wet basis of a corn sample having 100 grams and 82 grams wet and dry weights?

5%

Percent Head rice = 100% (Weight of whole grains) / Total weight

= 100% (25 kg) / (25 g + 305 g +170 g) = 5%

A dried palay sample was milled using a rubber roller laboratory rice mill. After milling, the weight of whole milled grains, broken milled grains, and hull were 25 g, 305 g and 170 g, respectively. The milled rice was classified as Class A. Determine the percent head rice.

400 kg/h

Solution:

Poil = Weight of crude oil collected / Total time

= 1,200 kg /3 h

= 400 kg/h

A 3.1-tonne capacity Jatropha oil expeller was loaded full with dried Jatropha seeds in 4 minutes. It produced 1200 kg of crude oil in 3 hours. What is its crude oil production rate?

300 kg/h

Solution:

Pcake = Weight of resulting cake produced / Total time

= (2,200 kg seed - 700 kg oil) /5 h

= 300 kg/h

A Jatropha oil expeller was loaded with 2.2 tonnes dried Jatropha seeds. It produced 700 kg of crude oil in 5 hours. What is its Jatropha cake production rate?

970 kg/h

Solution:

Pcake = [(Wt. of copra input - Wt. of crude oil collected )/ Total time] x Eff

= [(21,000 kg - 9,000 kg) / 12 h] x 0.97 = 970 kg/h

A 21-tonne capacity coconut oil expeller was loaded full with grated copra. It produced 9,000 kg of crude oil in 12 hours. What is the copra cake production rate of the machine at 97% cake collection efficiency?

894

Solution:

Wt = Input Rate x (Peak Operating Time + Lean Operating Time)

= [0.27 tonne/h][ (16 h/d x 30 d/mo x 3 mo/yr)+ (8 h/d x 26 d/mo x 9 mos/yr)]

= 894 tonnes /yr

How many tonnes of agricultural waste is needed annually to optimally operate a 27-ampere 9-kw vermi cast production shredder having a capacity of 0.27 tonne of waste per hour? It optimally operates 16 hours daily during the 3-month peak sunny months and 8 h/day at 26 days/month for the rest of the year.

150

As prescribed in PAES 419:2000, in constructing the walls of a warehouse for bagged storage of grains, the wall should use _____ mm thick concrete hollow blocks with 12 mm diameter reinforcing bars at horizontal and vertical spacing of 600 mm.

PD 1096

Known as the National Building Code of the Philippines.

Type IV

Type of the building that is made of steel, iron, concrete, or masonry construction.

6

PAES 419:2000 requires that a normal-temperature warehouse intended for storage of bagged grains shall have a minimum interior height between the beam and floor of ____ meters.

1

Under PAES 418:2002, in constructing a primary processing plant for fresh fruit and vegetable, the windowsill shall be at least _____ m from the finished floor line.

1.5

Under PAES 418:2002, in constructing a primary processing plant for fresh fruit and vegetable, the doors shall have a minimum width of _____ m.

2.4

Habitable rooms provided with artificial ventilation shall have ceiling heights of not less than ______ meters measured from the floor to the ceiling (PD 1096).

10x20x40

Smallest dimension in centimeters of concrete hollow blocks in the Philippines.

2.7

For buildings of more than one storey, the minimum ceiling height of the first storey shall be _____ meters and that for the second storey 2.40 meters and succeeding storeys shall have an unobstructed typical head-room clearance of not less than 2.10 meters above the finished floor (PD 1096).

Septic tank

All buildings located in areas where there is no sanitary sewerage system shall dispose their sewage to imhoff tank or ___________ and subsurface absorption field (PD 1096).

Imhoff tank

A tank for sewage consisting of an upper or sedimentation chamber with sloping floor leading to slots through which the solids settle to the lower sludge-digestion chamber.

10

Based on the Building Code, when excavating near adjoining buildings the owners of adjoining buildings shall be notified in writing at least how many days before excavation?

7

As provided in the Building Code, when curing concrete made from ordinary portland cement, the concrete shall be maintained above 10 degrees Celsius and in moist condition for the first how many days at least?

3

When curing concrete made from high strength portland cement, what is the minimum curing time in days as provided in the Building Code?

70%

What percentage of concrete strength is reached at the end of the first week?

2-3

The initial setting of concrete starts in the first how many hours after concrete mixing?

Batter board

Wood stick or board nailed horizontally at the stake which serves as the horizontal plane where the reference points of building measurements are established.

Locating boundaries

In building construction, which step comes next to checking building permit?

Whole plywood

To establish an accurate 90-degree corner in a building layout, what will you use?

Admixture

Material other than portland cement, aggregate, or water that is added to concrete to modify concrete properties.

176

What is the equivalent compressive strength of ordinary concrete in kg per square centimeter for 2,500 psi?

25

To attain about 3,000 psi compressive strength in non-air entrained concrete, how many liters of water should be added per bag of cement?

4-8

When using 0.75 inch nominal maximum size of coarse aggregate, what is the estimated percentage of air content by volume in concrete?

0.48

When made of normal weight aggregate, what should be the maximum water-cement ratio of concrete that is intended to be watertight when exposed to fresh water?

0.44

For a concrete agricultural structure made from normal weight aggregate and in contact with sea water, what should be the maximum water-cement ratio for it to be watertight?

3.7

The weight in kilograms of a 6-meter long standard 10 mm diameter reinforcing bar.

201.1

The cross-sectional area in square millimeters of a standard 16 mm diameter reinforcing bar.

0.2-0.3%

In a wall footing, the horizontal steel reinforcement is said to be normally adequate if steel cross sectional area relative to concrete cross sectional area is ________.

4

What is the least number of longitudinal bars in a tied concrete column?

16 mm

What is the minimum diameter of longitudinal bars in a tied concrete column?