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

The video below demonstrates that water will find its own level. An question requires this concept: An apartment block receives water from a nearby reservoir. A pump is necessary to lift the water into a storage tank at the top of the building. The gravitational field strength is 10 N / kg. How much energy does the pump supply to lift each kilogram of water into the tank? Solutions: 100J Water will always find its own level. Hence with or without the pump, the water level in the pipe in the building will be of the same level as the reservoir. Hence, the pump is only needed to pump water up a height of 10m only (instead of the 50m). Energy, E = mgh = 1 kg x 10 N/kg x 10m =  100 J

Answer: Option B Since water will naturally reach 40m high from the bottom of the apartment, you only need to pump the water up by a further 10 m. Energy needed = GPE = mgh = 1 x 10 x 10 = 100 J View this video to understand that when both ends of the tube are exposed to atmospheric pressure, the water levels on each end will be level.

At sea level (where most of us are), the standard atmospheric pressure is about 101325 Pa. The boiling point of water is at  100 oC which we are familiar with. But as you climbed up e.g. Mount Everest at 8,848 m, the pressure is low and the boiling point of the water is about 71oC. So that’s the hottest cofe you can have on top of the cold mountain! Hence as the pressure decreases, the boiling point of the water decreases. As with lower pressure, the water molecules requires lesser energy to break the intermolecular forces to escape into the atmosphere, hence boiling point is lower. This video shows the same effect. Using the syringe, the air is pumped out of the container to reduce the pressure. The water at 75  oC , (below the usual boiling point of 100 oC) will start to boil and you can observe the bubbles forming!

We have learned that silver smooth reflective surface is a poor absorber , poor emitter or a good reflector of infra-red radiation. How can we apply this concept to this suitation? 2022PPp1q17 Answer: Option D

https://mainichi.jp/english/articles/20230726/p2a/00m/0sc/014000c Dull black is the best absorber and best emitter of infra-red radiation. When we are outdoor under the sun, ideally we should wear light colours shirt like white or yellow, so that we wont feel so hot.

Hand boiler toy is a demonstration of thermal transfer and how the 3 states of matter interact. The coloured liquid inside is usually ethyl alcohol, which is a volatile liquid (i.e. a liquid with low boiling point). Similar to the alcohol swab you applied on hand during injection. Such liquid evaporates easily in room temperature or when heat is applied to it. Thermal energy flows from a region of higher temperature to a region of lower temperature . When we hold the boiler in our hand, the thermal energy from our hand (body temp about 37oC) is transferred to the lower bulb of the boiler. The ethyl alcohol evaporates and also due to heated air above the liquid, the air expands and the pressure increases . The air pushes the liquid down , hence pushing the liquid up the shaft into the top bulb . The bubbling of the liquid in the top bulb is not due to ‘boiling’ of the liquid. Rather, the gas in the lower bulb continues to expand and it goes to the top bulb, hence giving the illusion that the liquid is ‘boiling’.

First astronauts launched by SpaceX returned home safely on 3 Aug 2020.