Your house has a voltage of 120V. You want to estimate how much energy (in Joules) you use one morning. You wake up at 7am and leave your place at 9 am. The appliances turned on in your kitchen at breakfast time are:
•One hot plate: runs for 10 minutes, 6 A
•Refrigerator: 500W when the compressor is running (i.e. when it does the humming sound for 2 minutes every hour)
•10 light bulbs, used for two hours, 100W each.
•You use 150L of warm water (38ºC) heated up by the hot water tank from a temperature of 15ºC(150 L = 1.5 m^3). Warming up 1 litre of water by one degree takes 4186 J
Calculate the energy use of each appliance
hot plate=120*6*10/60
refer= 500(2/60)*2
lights- 10*100*2
water= 150*(38-15)*4186
add them up.
btw: not that it is needed, but 1m^3=1000L, the conversion given 150L=1.5m^3 is very wrong. 1.5m^3=1500L
To calculate the energy use of each appliance, we need to use the formula:
Energy (in Joules) = Power (in Watts) * Time (in seconds)
1. The hot plate:
Given that the hot plate runs for 10 minutes, which is equal to 600 seconds, and it has a current of 6 A, we can calculate its energy use:
Energy = Power * Time = (6 A * 120 V) * 600 s
2. The refrigerator:
The refrigerator operates for 2 minutes every hour when the compressor is running. So, we can calculate its energy use for the entire morning:
Energy = (Power * Time) + (Power * Time)
= (500 W * 2 min) + (500 W * 2 min)
3. The light bulbs:
Each light bulb has a power of 100W, and they are used for 2 hours, which is equal to 7200 seconds. So, we can calculate the total energy use of the light bulbs:
Energy = (Power * Time) + (Power * Time) + ... (10 times)
4. The hot water tank:
To calculate the energy used to heat the water, we need to determine the temperature difference (ΔT) and the volume of water (V). The temperature difference is (38°C - 15°C) = 23°C, and the volume is 1.5 m^3.
Energy = Volume * Density * Specific Heat Capacity * ΔT
Energy = 1.5 m^3 * 1000 kg/m^3 * 4186 J/kg°C * 23°C
By plugging in the values into the respective formulas, you can calculate the energy use of each appliance.