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Electronics Information

In an electronic circuit, a thermocouple can be used to:

open or close a circuit at a designated temperature

A thermocouple is a temperature sensor that consists of two wires made from different conductors. The junction of these two wires produces a voltage based on the temperature difference between them and can be used like a switch to open or close the circuit at a designated temperature.

Mechanical Comprehension

If input effort is 700 ft⋅lb, what output effort will be produced by a machine with a mechanical advantage of 5?

3500 ft⋅lb

Mechanical advantage is the ratio of output force to input force and tells us by how many times a machine multiplies input effort. So, a machine with a mechanical advantage of 5 will multiply an input effort of 700 ft⋅lb by 5 to produce an output effort of 3500 ft⋅lb.

General Science

Which of the following is the formula for power?

\(P = {w \over t}\)

Power is the rate at which work is performed or work per unit time: \(P = {w \over t}\) and is measured in watts (W).

Word Knowledge

Obnoxious most nearly means:

objectionable

Highly offensive.

General Science

The envelope of gases surrounding the planet is called the:

atmosphere

The biosphere is the global ecological system integrating all living beings and their relationships. This includes their interactions with the lithosphere (the rigid outer part of the earth, consisting of the crust and upper mantle), hydrosphere (all surface water), and atmosphere (the envelope of gases surrounding the planet).

Mechanical Comprehension

Lisa lifts a 25 pound box from the floor onto a loading dock 4 ft. off the ground. Sam slides the same box along a ramp to move it up another 4 ft. onto a flatbed truck. Who has done more work?

They have done an equal amount of work

Work is force multiplied by distance. Because both Connie and Sam moved the same weight the same distance they have done an equal amount of work. Sam employed the mechnacial advantage of an inclined plane so he exerted less effort to do the work but the amount of work done was still the same.

General Science

__________ is caused by a lack of Vitamin C.

scurvy

Scurvy is a difficiency disease caused by a lack of Vitamin C in the diet.

Mechanical Comprehension

If the green box weighs 30 lbs. and is 8 ft. from the fulcrum, how much force would need to be applied at the blue arrow to balance the lever if the arrow's distance from the fulcrum is 9 ft.?

26.67 lbs.

To balance this lever the torques at the green box and the blue arrow must be equal. Torque is weight x distance from the fulcrum so the equation for equilibrium is:

R_ad_a = R_bd_b

where a represents the green box and b the blue arrow, R is resistance (weight/force) and d is the distance from the fulcrum.

Solving for R_b, our missing value, and plugging in our variables yields:

R_b = \( \frac{R_ad_a}{d_b} \) = \( \frac{30 lbs. \times 8 ft.}{9 ft.} \) = \( \frac{240 ft⋅lb}{9 ft.} \) = 26.67 lbs.

Shop Information

When cutting hard metals with a hacksaw you should choose a blade with __________ teeth per inch (TPI).

high

Blades with more and smaller teeth (high TPI) cut harder metals more effectively while blades with fewer and larger teeth (low TPI) cut softer metals more effectively.

Electronics Information

Which of the following will help to prevent a short circuit?

fuse

Fuses are thin wires that melt when the current in a circuit exceeds a preset amount. They help prevent short circuits from damaging circuit components when an unusually large current is applied to the circuit, either through component failure or spikes in applied voltage.