test 2 physics

Evaporation vs Boiling

• Evaporation: only some surface particles escape (not all, and no bubbles).

• Boiling: happens when vapour pressure = atmospheric pressure, and it occurs throughout the liquid.

Why can water evaporate at 25°C? What is the effect of the evaporation?

Some particles have enough kinetic energy even at lower temperatures. Only the surface particles with the most energy can escape. When the fastest particles leave, the average kinetic energy drops, so the temperature decreases.

Factors that affect rates of evaporation

Reduced atmospheric pressure, Dry air, Breeze

Reduced atmospheric pressure

When atmospheric pressure decreases, the rate of evaporation increases because water molecules escaping from the surface are less likely to collide with air molecules and be forced back into the liquid. With fewer air particles above, it’s easier for these molecules to stay in the gas phase

Dry air

In dry air, there’s more space between the air molecules, so there’s less chance of collisions between water molecules and air molecules. This allows more water molecules to escape into the air instead of being forced back into the liquid.

Breeze

A breeze removes the humid air near the surface of the water and replaces it with dry air. In dry air, there’s more space between air molecules, so there are fewer collisions between the water molecules and air molecules. This makes it easier for water molecules to escape into the air instead of being forced back into the liquid.

What is humid air

Humid air near the surface has more water molecules, making it harder for new molecules to escape

Expansion Valve and Low Pressure:

The refrigerant starts as a liquid. As it passes through the expansion valve, it undergoes a pressure drop, which causes it to expand and change into a gas. The refrigerant is now under low pressure.

Absorption of Heat:

During this phase change from liquid to gas, the refrigerant absorbs heat energy from the fridge and its contents. This is why the inside of the fridge gets colder—heat is being removed from the items inside.

Compression Valve and High Pressure:

The refrigerant gas then enters the compressor (compression valve), where it is compressed. This raises its pressure and temperature, turning it into a high-pressure gas.

Condensation (Releases Heat)

As the high-pressure refrigerant gas travels through the pipes and into the condenser coils, it cools down and condenses back into a liquid. During this process, the refrigerant releases heat to the surroundings, which is why the coils on the back of the fridge are warm.

Heat Dissipation via Coils:

The large surface area of the black coils (which are good at radiating heat) helps the refrigerant release heat efficiently to the surrounding environment, cooling the gas down and completing the cycle.