Electricity - 2.4.2 Energy Transfers in Everyday Appliances (GCSE Physics AQA)
Energy Transfers in Everyday Appliances
Transferring Energy
Everyday Appliances
- Appliances can transfer energy. Everyday electrical appliances in our homes are designed to bring about energy transfers. For example, kettles, microwaves and hairdryers can all convert electrical energy into other forms of energy, which we can then use.
- The amount of energy transfer can vary. Depending on various factors, the energy transferred by an appliance can vary. These are:
- Time – the length of time an appliance is switched on for is very important. The longer an appliance is switched on for, the hotter it will get. As the appliance tries to cool down, it will convert more of the electrical energy input into a thermal energy output. This thermal energy is seen as ‘wasted’ energy, since it is not our desired output. In this way, the longer an appliance it switched on for, the less efficient it becomes.
- Power – different appliances will have different power ratings. A more powerful appliance will use more electricity than a less powerful appliance. However, we still have to be mindful of efficiency. Even if one appliance is more powerful than another, it might have a less efficient energy transfer (i.e. the energy output will have a lot of thermal energy, which is ‘waste’ energy).
Examples of Energy Transfers
- Electric motors use kinetic energy. Electric motors will convert electrical energy from batteries into kinetic energy. This kinetic energy can be used to spin the blades of a fan or move electric cars. The wasted energy here will be mainly in the form of sound and thermal energy.
- Heating devices use thermal energy. Heating devices will convert the electrical energy from the mains a/c (alternating current) supply into thermal energy. This thermal energy can be used in the heating element of a toaster. The wasted energy here may be in the form of sound energy.
Work Done
Work is done when charge flows in a circuit.
As with any form of ‘work’, energy is transferred when electrical work is done. We will calculate the energy transferred by electrical work in the next tutorial.
We can calculate energy transferred in one of two ways.
Using Power and Time
Power tells us the energy transferred per second. To find the total energy transferred over a sustained period of time, we need to multiply power by the total number of seconds.
Where:
- energy transferred, E, in joules, J
- power, P, in watts, W
- time, t, in seconds, s
Question: An electric lamp transforms 400 J in 8 s. What is its power?
1. Write out the equation.
In this instance, we need to rearrange the equation to make power the subject.
E = Pt
P = E / t
2. Substitute in the numbers.
P = 400 / 8
P = 50 Watts
Question: A motor has a power of 12W. How much energy does the motor transfer in 1 minute?
E = P t = 12 x 60 = 720J
Question: Ankit is deciding between purchasing a lamp from Aryaland and a lamp from Makam Bulbs. The lamp from Aryaland has a power of 6W, whilst the lamp from Makam Bulbs has a power of 10W.
Assuming 100% efficiency in both lamps, what is the difference in the kilojoules (kJ) of energy produced in 2 hours?
The difference between the powers: 10W – 6W = 4W
We need the answer in seconds, hence 2 hours = 120 minutes x 60
seconds = 7200 seconds
E = P x T = 4 x 7200 = 28800
To convert to kilojoules: 28800/1000 = 28.8
Using Charge and Voltage
We can also calculate energy transferring using charge and potential difference. Let us look at the first equation, E = Pt.
We can substitute in P = VI into the equation E = Pt, to give E = VIt.
Current is just the rate of charge flow, I = Q/t. We can substitute in I = Q/ t into E = VIt, to give E = V x Q/t x t. This simplifies to E = VQ.
Where:
- energy transferred, E, in joules, J
- charge flow, Q, in coulombs, C
- potential difference, V, in volts, V
Question: A motor has a power of 12W. How much energy does the motor transfer in 1 minute?
1. Write out the equation.
E = QV
2. Convert into seconds.
In the question, we have been given a time in minutes, therefore we need to convert into seconds.
1 minute = 60 seconds
3. Substitute in the numbers.
We need to use the value for time in seconds (which we have just calculated).
E = 12 x 60
E = 720 J
Power Ratings and Energy
- The power rating is a maximum value. When a customer buys an electrical device, it comes with a power rating. This is the maximum value at which the appliance can be used safely. We also know that power is the rate of energy transfer. Therefore, the power rating also tells us the maximum rate at which energy can be transferred when using the appliance.
- Power ratings can vary. Some power ratings are low, whilst others are high. We know that electrical device can store energy. A high power device will be transfer more of this energy per second, therefore doing more work. By doing so, a high power device will require more electricity.
FAQs
Energy transfer in everyday appliances refers to the way in which energy is converted and transferred from one form to another in common household devices. This is a key concept in GCSE Physics and is important for understanding how appliances work and how energy is used in daily life.
There are many examples of energy transfers in everyday appliances. Here are a few:
Refrigerator: A refrigerator transfers energy in the form of electricity to a compressor, which compresses refrigerant gas. This process causes the temperature of the gas to increase, and then it is passed through a condenser coil where it releases heat to the surrounding air. As the gas cools, it turns into a liquid, which then expands through an evaporator coil in the refrigerator. This process absorbs heat from inside the fridge, cooling it down.
Microwave: A microwave transfers energy in the form of electromagnetic waves to food. The waves cause water molecules in the food to vibrate, generating heat and cooking the food.
Hair dryer: A hair dryer transfers energy in the form of electricity to a heating element, which heats up the air that is drawn in. The hot air is then blown out of the dryer, transferring the heat energy to the hair.
Electric kettle: An electric kettle transfers energy in the form of electricity to a heating element, which heats up the water inside the kettle. As the water heats up, it turns into steam and escapes through a spout.
Gas stove: A gas stove transfers energy in the form of heat from burning gas to a pot or pan placed on the burner. This process heats up the food inside the pot or pan.
These are just a few examples, but energy transfers occur in many different appliances and devices that we use every day.
The different forms of energy involved in energy transfer include electrical energy, thermal energy, kinetic energy, and potential energy.
In a light bulb, electrical energy is converted into light and heat energy through the process of resistance.
In a refrigerator, thermal energy is transferred from the inside of the fridge to the outside, thereby cooling the interior. This transfer of energy takes place through the use of a refrigerant and a compressor.
In a washing machine, electrical energy is transformed into mechanical energy, which powers the movement of the drum and agitator. The movement of the drum creates kinetic energy, which helps to clean the clothes.
In a microwave oven, electrical energy is transformed into electromagnetic radiation, which heats up the food.
In an electric kettle, electrical energy is transformed into thermal energy, which heats up the water. The thermal energy is transferred to the water through conduction.
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