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TGR1: What speeds up evaporation?
The topic of evaporation was introduced in G1. If you want to review that section with your class before going on, return to the main content and use the drop -down menu at the top right to go straight to the start of G1. You can use the same method to get back to R1 quickly.

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Notes on ‘Think for Yourself’ questions

Why does a bigger surface area increase the rate of evaporation?
The particles leave from the surface. With a bigger surface area, more particles can leave at the same time.
Why does water evaporate faster in a warmer room?
The water is warmer and the air is warmer. Only high energy water particles can leave on their own, and the
warmer the water, the more high energy water particles there are. Only high energy air particles can knock out
medium and low energy water particles: the warmer the air, the more high energy air particles there are.

Look at the animation again. Notice that some water particles are returning. If 50 water particles leave and 20
water particles return every second, what is the overall rate of evaporation?
30 particles per second (These numbers aren’t ‘real’: they just illustrate the point).
How would a fan affect the rate at which water particles leave the surface?
The rate would not change because the number of high energy water particles and high energy air particles would
not be changed (because a fan does not warm up the room).

So how can a fan speed up the rate of evaporation?
It creates a breeze, which reduces the number of water particles which can return. The bigger the difference in
numbers leaving and returning, the faster the rate of evaporation.

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