🔍 Key Concepts
• Use the psychrometric (humidity) chart: dry bulb along the bottom axis, wet bulb along the left axis, and relative humidity curves labeled 10%, 20%, 30%, etc.
• A larger difference between dry bulb (DB) and wet bulb (WB) temperatures means drier air (lower relative humidity); a small difference means more humid air.
• On this chart, you must find the intersection of the 78°F dry bulb vertical line and the 62°F wet bulb slanting line, then read the closest % curve.
💭 Think About
• First, mark 78°F on the dry bulb scale at the bottom and imagine (or lightly draw) a vertical line upward. Where on the chart does this line pass through?
• Next, locate 62°F on the wet bulb scale at the left and follow the corresponding slanted constant-wet-bulb line down and to the right. About where does it cross your 78°F vertical?
• When you find that intersection point, which relative humidity curve (10%, 20%, 30%, 40%, etc.) runs closest through that point? Is it nearer the low-percent curves or the high-percent curves?
✅ Before You Answer
• Confirm you are reading dry bulb from the bottom axis and wet bulb from the left axis, not from the right-hand dew point scale.
• At the intersection point, double‑check which labeled humidity curve (10%, 20%, 30%, 40%, etc.) is actually passing through or nearest that point.
• Before choosing, ask: with a 16°F difference between dry and wet bulb, should the air be very humid (near 80%) or moderately dry (near 20–40%)? Use that to rule out unlikely options.