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.

Question 01

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

Question 02

Solutions: Option D

Question 03

Solutions: A

Question 04

Question 05

Solution: Option C

How to show wavefronts in a ripple tank

Wavefront is an imaginary line which joins all identical adjacent points (e.g. crests) in phase.

Note that the distance between two successive wavefronts is the wavelength.

Wavefront can be created in a ripple tank.

The video below shows how horizontal wavefront is created.

The video below shows how other types of wavefronts are produced

Determine the motion of the particles on transverse wave

Instead of imaging how the particles will move and guess their motion, there is a technique which can help you to determine that.

In addition, when particles are in phase, it means that both particles on the wave have the same velocity and same displacement. It means both have the same speed in the same direction and same distance and direction away from the rest position.

Particles that are out of phase means both are having the same speed but in opposite direction.

Refer to the video below to find out more.

Question 01: 2005/2008 PP P1 Q20/Q18

Question 02: 2018 PP P1 Q24