O calculationgivesenergyelectric consumed by household appliances can be done based on the potency and in the time in which each of these devices remains switched on, so that the electrical energy consumed is calculated in kilowatt hour (kWh). Knowing how to calculate energy consumption is of great importance for a conscious use of electrical energy. Furthermore, this is a very popular subject in the tests of the And either.
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How to calculate energy consumption
To calculate the consumptiongivesenergyelectric, just know what the potency the device, as well as the time that this device works. The formula we use to calculate electricity consumption is as follows:
P – power (kW)
t – usage time interval (h)
This formula shows that the consumption of electricity, which is measured kWh, can be calculated by the product between the potency (in kW), which is usually informed on the appliance, and the operating time interval of that appliance (in hours).
As an example of calculation, we will estimate what the consumptioninenergyelectric of a conventional shower. For this, let's consider a 4500 W (4.5 kW) shower that is used 1.5 h (1h and 30 minutes) per day for 30 days:
The calculation made above indicates that this shower consumes about 202.5 kWh per month. To know the impact of this consumption on the price of the electricity bill, it is necessary to verify what the average of the kWh price on your electricity bill, as this value changes according to the region of Brazil. We are going to use here the value of R$0.70 per kWh. Follow:
The result obtained gives us an idea of the consumption monthly energy for one electric shower, which is one of the biggest villains in monthly electricity consumption. Some strategies can be used to minimize spending on baths, such as reducing their duration, using the shower at lower temperatures or even use other forms of water heating, such as gas or solar heating.
See too:Tips for saving electricity
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Exercises on electricity consumption
Question 1 - (PUC-Campinas) A few years ago, residential lighting was predominantly done using incandescent lamps. Currently, paying attention to the policy of preservation of natural assets, these lamps are being exchanged for other types of lamps that are much more economical, such as compact fluorescent and LED.
In a home, 10 incandescent bulbs of 100 W were used, which were turned on for an average of 5 hours a day. These lamps were replaced by 10 compact fluorescent lamps that consume 20 W each and are also turned on for an average of 5 hours a day. Adopting the value of R$ 0.40 for the price per kilowatt-hour, the savings that this exchange provides in a month of thirty days is:
a) BRL 18.00
b) BRL 48.00
c) BRL 60.00
d) BRL 120.00
e) BRL 248.00
Template: letter B.
Resolution:
First, it is necessary to find out what was the monthly consumption of electricity before changing the light bulbs. Then we must find out what was the consumption after the switch. Knowing this, it is enough to calculate the difference between these two consumptions and then, multiplying the result obtained by the value of kWh, we arrive at the monthly savings.
See the calculation of monthly energy consumption before changing the lamps:
Then, we will do the calculation to find out the consumption after changing the lamps:
Now, we just need to take the difference between these two consumptions, which is 120 kWh, and multiply it by the kWh value, which is R$ 0.40. By doing this, we will find that the savings on the energy bill were equal to R$48.00.
See too: Physics formula tricks
Question 2 - (Enem) Among the numerous recommendations given for saving electricity in a home, we highlight the following:
- Replace incandescent light bulbs with compact fluorescent ones;
- Avoid using the electric shower with the switch in the "winter" or "hot" position;
- Accumulate an amount of clothes to be ironed at once;
- Avoid using multiple outlets to power multiple devices simultaneously;
- Use wires with diameters recommended for your purposes in the electrical installation.
The common feature of all these recommendations is the proposal to save energy by trying to reduce:
a) the power of electrical appliances and devices.
b) the usage time of the devices and devices.
c) the consumption of electrical energy converted into thermal energy.
d) the consumption of thermal energy converted into electrical energy.
e) the consumption of electrical energy through leakage currents.
Template: letter C.
Resolution:
All the recommendations that have been given suggest that electricity consumption can be reduced if we avoid unnecessary energy losses due to the Joule effect. The Joule effect explains that the passage of electrical current through resistive means produces heat, which constitutes a waste of electrical energy, so the correct alternative is the letter C.
Question 3 - (UTFPR) On a cold day, a certain electric shower is turned on to dissipate a power of 7200 W. If the time it stays on is ten minutes, the electricity it consumes, in kWh, is:
a) 1.5
b) 1.8
c) 2.2
d) 3.0
e) 1.2
Template: letter e.
Resolution:
Solving the exercise requires doing some unit conversions in order to find the answer in the proper unit, kWh. Therefore, we must transform the power, which is in watts, into kilowatts, dividing it by the factor 1000, in addition to transforming the time interval into hours, dividing it by 60. Check the calculation:
The consumption obtained is 1.2 kWh, so the correct alternative is the letter E.
Question 4 - (IFSP) When entering a building supply store, an electrician sees the following ad:
SAVE: 15W fluorescent lamps have the same brightness (illumination) as 60W incandescent lamps. |
According to the ad, in order to save electricity, the electrician changes a light bulb incandescent by a fluorescent and concludes that, in 1 hour, the electric energy savings, in kWh, will be in:
a) 0.015
b) 0.025
c) 0.030
d) 0.040
e) 0.045
Template: letter e.
Resolution:
To solve the exercise, it is necessary to take into account the difference between the wattages of the two lamps, which is 45 W; then divide this value by the factor 1000, since we want to obtain the amount of energy saved in kWh, and do the following calculation:
The result obtained indicates that the energy consumption savings during the period of one hour was equal to 0.045 kWh, so the correct alternative is the letter E.
By Rafael Hellerbrock
Physics teacher
