In theory, we have learned that Dull (matt/rough) and black surface is a good emitter and good absorber of infrared radiation . In this simple demonstration, the container sides are painted white matt, silver smooth and black matt. Hot water is poured into the container and the thermal energy is conducted to the whole container. The temperature of the container is more or less uniform. Using a infrared thermometer, we measure the temperature of the different surfaces. From this simple demonstration, we can conclude that dull black surface is the best emitter of infrared radiation and smooth silver surface is the worst emitter of infrared radiation .

This simple toy is made possible using convection current in the air. The ‘fan’ of the carousel is similar to the windmill we are familiar with.  Just that the kinetic energy of the wind is created by the stream of hot air rising up from the bottom. It is the opposite of an electric fan.

The video include 3 different light experiments which involve glass block and pins. Most students faced difficulties in locating the pins through the glass block. It is important to close one eye and use your master eye to view. Hope this video helps! In experiments like this, the sources of error include: – the holes created by the pins are too big, hence the line drawn using the two holes may not be very precise, hence affecting the distance/angle measured (depends on experiments) – When putting back the glass block back on the paper, the position may be not exactly the same, hence affecting the angle/distance measured. As a precaution , it is good to ensure that the distance between the two pins are more than 4 – 5 cm. With the holes further apart, the line drawn will be more accurate.

Refer to the video below for the setting up of the apparatus. Why do you need a variable resistor (rheostat)? Without the variable resistor, you will have only one set of current I and potential difference V readings. Using the formula R = V/I, you are able to find the unknown resistor. But this method is not so accurate . Hence, to make it more accurate, we include a variable resistor to control the size of the current through the circuit. Thus having different readings of the potential difference V across the unknown resistor . Instead of just one set of readings of I and V, we now have about 5 sets. This allows us to plot a graph of V against I. By finding the gradient of the best fit line , we are able to find the resistance more accurately. [gradient = V / I = R, hence the gradient of V-I graph represents resistance R] For pure metallic conductor , like the fixed resistor R, it obeys the Ohm’s Law , hence it is an ohmic conductor. From the graph, the current I flowing the conductor is directly proportional to potential difference V across the conductor, provided physical conditions like temperature remains constant. [the graph is a straight line with constant gradient, and passes through the origin]

The variable resistor (rheostat) is a device to control the size of the current by adjusting the resistance on the variable resistor . Hence just device can be used to adjust the brightness of the bulb or the fan speed.