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.

Other examples in our daily lives: In some supermarket, the seafood are placed outside of air-conditioned place. The seafood is kept cold by putting crushed ice covering the seafood to keep the them cold and fresh. Refer to this Sci Physics question N2008P2Q6(b) Solutions:  For the solid that does not melt, when thermal energy is absorbed from the surrounding  food, its temperature starts to rise. So it is not so effective at keeping the food cool. For ice-pack, when thermal energy is absorbed from the surrounding food, it starts to melt. During melting process, a much larger quantity of thermal energy is absorbed from the food to melt per unit mass of ice, the temperature remains constant at 1oC, and the melting process is long. Hence ice-pack is more effective at keeping the food cool.

This simple circuit involves a resistance wire on the meter rule and the use of jockey tapping at different length L on the resistance wire. Note that this is not a potential divider. Rather this set up works like a variable resistor (rheostat) in the circuit. When the switch is closed (jockey NOT tapping on resistance wire), there is no current flowing as voltmeter (infinity resistance) is connected in series with the ammeter and the battery. Hence the voltmeter is showing the battery’s electromotive force (emf) of 3.0 V. When the switch is closed and the jockey is tapped on the resistance wire on the ruler, the longer the L (length of resistance wire) , the higher the resistance of the circuit , the higher the potential difference (voltmeter) across the resistance wire and the smaller the current through the ammeter . Hence the tapping of the jockey on the resistance wire is similar to adjusting the resistance on the variable resistor. (If you are wondering why the voltmeter is not showing the emf of the battery when the jockey touches the resistance wire L, it is because in reality there is internal resistance in the battery or even in the connecting copper wire. For olevel theory we assume no internal battery resistance or resistance in copper wire or ammeter). To learn how to set up the experiment, refer to the video below. Both ammeter and voltmeter have two terminals , ( positive and negative ). The conventional current must flow into the positive terminal (+) of the meters and out of the negative terminal (-) .   If the connection is the opposite, the needle will deflect below the zero marking. Refer to the video below. Sometimes, the connection terminals on the voltmeter and ammeter are different. Likewise, different types of wire with different connection heads have to be used. Refer to the video to see how are they connected in general.

2019PPP1Q33 Ans: Option B 2007PPP1Q28 Ans: Option B Torch lamp or bulb is a non-ohmic conductor . The V-I graph has an increasing gradient indicating resistance increases. As the current through the filament of bulb increases (due to p.d across increases) , temperature increases and resistance increases. For an ohmic conductor , the graph of V against I is a straight line with constant gradient and passes through the origin . Something to thing about: What if there is an option E whereV increases from 0, 1, 2, 3I increases from 0, 6, 10, 12 respectively. The graph will be a typical ohmic graph, similar shape to option B, but will you choose E? Refer to the last section of the video from 4:37 s.