Correct: B) The total rate at which gas enters the system from all sources

Correct: C) The bulk gas has been removed and the remaining gas load comes from slower sources like surface water and outgassing

Correct: C) Thermal expansion of the chamber walls

Correct: B) Outgassing rate decreases over time because gas trapped deeper in materials takes longer to diffuse to the surface

Outgassing is a diffusion-limited process. Gas molecules near the surface desorb quickly, but molecules trapped deeper in the material must diffuse through the bulk before they can be released. This means the "easy" gas comes off first and the rate decreases steadily over time — hours or even days. It never fully stops, but it continuously diminishes.

Correct: C) A real leak connects the chamber to an unlimited gas source (atmosphere), while a virtual leak releases gas from a trapped volume that eventually empties

A real leak is a physical pathway to atmosphere — it provides a constant, unlimited gas flow. A virtual leak is a trapped pocket of gas (e.g., gas in a blind bolt hole or between poorly fitted surfaces) that slowly releases into the chamber. The virtual leak eventually empties; the real leak never does. This difference shows up in rate-of-rise testing: real leaks produce a constant rate, virtual leaks produce a decreasing rate.

Correct: C) Distinguish between outgassing and leaks by observing how pressure rises in ISOLATED state

A rate-of-rise test isolates the chamber (both valves closed, pump off) and records how pressure changes over time. The shape of the pressure-versus-time curve reveals the gas source: a decreasing rate indicates outgassing (normal), a constant rate indicates a real leak (problem). This is the single most important diagnostic tool in vacuum troubleshooting.

Correct: B) A real leak — gas is entering at a constant rate from an unlimited source

A constant rate of rise (0.5 mbar/min at every measurement) is the signature of a real leak. Atmosphere is an unlimited gas reservoir, so the leak provides a constant flow regardless of how long you wait. If this were outgassing, the rate would decrease over time. This finding should be escalated with the data: "Constant rate of rise at 0.5 mbar/min in ISOLATED state — suspect real leak."

Correct: A) True

A decreasing rate of rise is the classic outgassing signature. Gas molecules near the surface desorb quickly (higher initial rate), while deeper molecules take longer to reach the surface (decreasing rate over time). This is normal behaviour and does not indicate a leak. The key diagnostic question is always: is the rate constant (leak) or decreasing (outgassing)?

Correct: B) Surface-adsorbed water

Once the bulk gas has been removed (above ~1 mbar), surface-adsorbed water becomes the dominant gas load. Water molecules stick to every internal surface and slowly desorb under vacuum. This is why pumpdown slows dramatically in this range — the pump is fighting water desorption, not bulk gas. Permeation is usually negligible in rough vacuum, and leaks are abnormal rather than the default gas source.

Correct: B) To prevent airborne particles from being drawn into the chamber during controlled venting

R1-FLT-VENT is a sintered metal filter on the vent line. During controlled venting, the pressure differential draws atmospheric air into the chamber. Without the filter, dust, pollen, fibres, and other particles would be carried into the chamber along with the air. The filter captures these particles before they reach the chamber. The oil mist filter (R1-FLT-EXH) is the one that deals with pump oil — it sits on the exhaust line, not the vent line.

Correct: C) Contamination (such as hydrocarbon film or excess water) is increasing the gas load above normal levels

An elevated base pressure — higher than the system normally achieves under the same conditions — is a classic contamination signature. The pump is working normally, but the gas load from contamination (oil film, water, or other volatile material on surfaces) exceeds what the pump can remove. This creates a new, higher equilibrium pressure. The system isn't broken; it's dirty.

Correct: B) Oil vapour from the pump migrates backward through the foreline toward the chamber, especially at low pressure with no gas flow

Backstreaming occurs when oil vapour from an oil-sealed rotary vane pump (like R1-P-RP) travels backward along the foreline toward the chamber. This is most likely when the pump runs at low pressure with zero gas load — there's no gas flow to push the oil vapour back toward the pump. The oil mist filter (R1-FLT-EXH) prevents oil from reaching the workspace through the exhaust, but backstreaming moves in the opposite direction — toward the chamber.

Correct: B) False

"Visually clean" is not the same as "molecularly clean." Fingerprint oils from bare-hand handling, trace solvents from cleaning, and adsorbed water from humid air are all invisible to the eye but produce significant gas load under vacuum. A fingerprint-sized oil deposit can dominate the outgassing of an otherwise clean chamber. Clean handling — gloves, clean tools, proper drying — is a discipline, not just a visual check.

Correct: C) The types and relative quantities of different gas species present in the chamber

A standard gauge like R1-G-CH tells you the total pressure — how much gas is present. An RGA breaks that total down by molecular species: how much water, nitrogen, oxygen, hydrocarbons, etc. This tells you what kind of gas is causing a problem, which points you toward the source. For example, nitrogen + oxygen in atmospheric ratio means an air leak; dominant water means surface desorption; hydrocarbon fragments mean pump oil contamination.

Correct: C) A larger pump may help slightly, but the most effective approach is usually to identify and reduce the gas load (fix leaks, clean contamination, allow more outgassing time)

Base pressure is determined by the ratio of gas load to pumping speed. A bigger pump increases the denominator, but if the gas load is dominated by contamination or leaks, the improvement is marginal. Fixing the gas source — sealing a leak, cleaning oil contamination, or allowing more time for outgassing — addresses the numerator and is usually far more effective. A small pump in a clean system will outperform a large pump in a contaminated one.