Technical Measurements Flashcards

One footcandle of illumination is defined as:

Answer: One lumen per square foot

A footcandle is one lumen uniformly distributed over one square foot.

A light meter reads 50 footcandles. Approximately how many lux is that?

Answer: 538 lux

One footcandle equals about 10.76 lux, so 50 fc ≈ 538 lux.

An increase of 10 decibels in sound level is generally perceived as:

Answer: About twice as loud

Because the decibel scale is logarithmic, a 10 dB increase is perceived as roughly a doubling of loudness.

Under OSHA, at what 8-hour time-weighted average noise level must a hearing conservation program begin?

Answer: 85 dBA

OSHA's action level of 85 dBA TWA triggers a hearing conservation program; 90 dBA is the permissible exposure limit.

A lobby measures 30 feet by 40 feet. How many square yards of carpet are needed, excluding waste?

Answer: 133.3 sq yd

1,200 sq ft divided by 9 sq ft per sq yd equals about 133.3 sq yd.

A tank holds 100 cubic feet of water. Approximately how many gallons is that?

Answer: 748 gallons

One cubic foot holds about 7.48 gallons, so 100 cu ft ≈ 748 gallons.

An infrared thermometer gives inaccurate readings on a shiny copper pipe. What is the most likely cause?

Answer: Low emissivity of the polished surface

Shiny metals have low emissivity and reflect surrounding infrared energy, causing false readings.