Team+3_display

Er Yuan Zhi 4S406, Li Zongchen 4S417, Tay Hanyang 4S429


 * ** Question 2 ** || ** Power / kW ** || ** Time of cooking / min ** || ** Total Energy Input /K J ** ||
 * Conventional Stove || 84 || 4 || 20160 ||
 * Microwave || 87 || 3 || 15660 ||

__ Thermal Efficiency __

__ Energy Wasted __ Stove: 20160KJ – 78.66 KJ = **20081.340 KJ** Microwave: 15660KJ – 41.945 KJ = **15618.055 KJ**

__ Time that a 100W light bulb can be burned using the wasted energy __ Stove: Almost **56 hours** Microwave: About **43 hours**

__ Findings and reflections __ This shows that a huge amount of energy is wasted as heat energy is transferred from the cooker to the popcorn, as shown in the extremely low efficiency of the cookers (each being lower than 3%).

In the stove, the electricity is passed through a metal poor conductor of electricity, which causes the electrical energy to be converted to heat energy due to the resistance. The heat is absorbed by the metal plate above it, which then heats up the aluminium popper resting on it. However, not all the heat is transferred to the popper as the hot plate also heats up the air around it through radiation, convection and conduction, especially if the hot plate is bigger than the popper. The popper then transfers heat to the popcorn, further providing a channel for heat energy loss, since heat energy absorbed by the popper is also lost through the same means to the surrounding air.

In the microwave oven, not all of the microwaves are absorbed by the popcorn package and most are absorbed by the oven itself or escape into the surroundings, especially since the package only occupies a small amount of space in the oven. Despite this, the microwave continues to emit microwaves throughout the oven, thus wasting energy.

The heat energy is actually lost. According to the law of conservation of energy, energy cannot be destroyed or created. This heat energy that is “lost” is actually used to heat up the surroundings or the cooker, that does not get transferred to the popcorn itself and hence this heat energy is not used to heat the popcorn itself, resulting in a low efficiency of the cookers. Thus, the heat energy is not lost but is wasted, since the heat energy is not channelled into a useful avenue to perform the function it is meant to.

We realise that so much energy is wasted during a simple everyday action such as using the microwave, and in such a short span of time. The low efficiency of our electrical appliances has made us more aware of our energy expenditure and the need to conserve electricity.

__ Energy lost indirectly __ __ Energy obtained from natural resources __