1. Boiling point of a substance increases with increase in pressure. Inside the pressure cooker, pressure is more than atmospheric pressure.

2. We know that boiling point of water at atmospheric pressure is 100.

3. So, boiling point of water is also above 100 inside pressure cooker. This means that food will now cook at higher temperature than 100.

4. So, by increasing the pressure and the boiling point we are reducing the time taken for food to cook. Hence, cooking is faster in pressure cooker than in open vessel.