Evan's Space

Wonders of Physics

Leave a comment

When to use the concept PV = constant and P1V1 = P2V2 to solve?

When temperature is constant (for o-level), when a fixed mass of gas (fixed number of air molecules) is compressed in a closed system (e.g. piston), the volume V decreases and pressure P increases, and vice versa.

But when you multiply pressure and volume, PV, it is always a constant.

PV = constant

Hence we can always equate the PV of the first scenario = to the PV of the second scenario, provided there is no addition or removal of air molecules from the system.

Hence, you have P1V1 = P2V2

The followings are 4 different questions which require this concept to solve. Do revise them.

Solutions: Option D (refer to the worked solutions below)

Solutions: Option D

Solutions: A




Leave a comment

Different kind of sounds

Students tend to think that ultrasound is a totally different kind of wave, or it is part of the electromagnetic spectrum, which is wrong!

The different kind of waves below are just different kind of sounds. So the properties of sound apply to all. Ultrasound is also sound wave, just that the frequency is greater than 20 kHz which is outside the range of audible frequencies for us.

different type of sounds