Theory of Electric and Microwave Ovens: Chapter 2
Electric oven
In this module, we will learn the details of an electric oven. We will learn: What an electric oven is, How it works, and Uses of an electric oven. Skip to quiz!
Introduction to Electric Oven
An oven that uses electrical energy to heat the food is known as an electric oven. The electric oven uses electrical energy, and it converts the electricity into heat using heating elements. The electric oven has multiple cooking methods as per the heating method used in it.
An oven's functions increase when there are two or more heating elements. Nowadays, electric ovens are also known as conventional ovens. The electric oven has racks, a convection fan, heating elements, and knobs to set the temperature and cook time.
The principle used in an electric oven is electrical energy. An electric oven produces heat electrically using a heating element in the form of coils and tubes. The heating element converts electrical energy into heat through the process of resistance.
Nowadays, the electric oven consists of an Electronic Printed Circuit (PC) board and is known as an Electronic oven. The electronic oven is an oven with a PC board/timer assembly with relays onto the board.
Components of an Electric Oven
The main components of an electric oven are
Cabinet,
Heating element,
Thermostat,
Timer, and
Power regulating switch.
Let us see the working of each component.
The oven cabinet is the outer metallic body of the oven. The metal box body is composed of
an outer shell,
a middle layer, and
an inner container.
The three-layer structure forms a separate air cavity between the inner layer’s front and back sides.
An insulating expanded perlite product is filled in the outer cavity. The insulating material helps to reduce the outer shell's temperature and prevents it from heating. Similar to a thermo-flask which has multiple layers to keep the tea or coffee hot for a longer time.
A spring structure is arranged below the door to cause the door to be pressed on the door frame at all times to have better sealing properties. This prevents the oven cavity to do not lose any heat and it is sealed from the outside air.
Recall that the broil element is typically found at the top of the oven cavity and provides direct heat to the top of food for broiling. A broiler is a section that provides high, direct heat like a grill.
Broiling places food close to the oven’s heating element so that it can quickly cook, brown, char, or caramelize. Broil elements can give food more complex flavors or help you achieve certain textures.
A thermostat is a device that measures the temperature inside the oven’s cavity. A thermostat is similar to a thermometer that can measure very high temperatures in an oven.
The thermostat is connected to a capillary tube which consists of gas. The gas expands when there is a rise in temperature until the desired temperature is achieved.
Working of an Electric Oven
The electric oven consists of a control board, temperature sensor, broil element, and bake element. The user provides the temperature and time. The control board sends the 120V current to both the broil and bake heating element.
The oven is preheated, and the control board monitors the temperature sensor using an oven control thermostat. The cycle is repeated and controlled by the control board until the desired temperature is achieved.
The broil setting uses broil elements only. Both the elements are used in the bake setting, and the bake element generates most of the heat. A convection oven fan circulates the heat all around the oven to bake or cook the food evenly.
Use of an Electric Oven
Ovens use electricity and can heat to a very high temperature. So it is not advisable to leave the food cooking in the oven unattended. Don’t use the oven as a storage cupboard – someone might forget and turn it on. Make sure to keep the oven clean from grease and splatters of food that can catch fire.
Never use water on a kitchen grease fire; use a wet cloth to extinguish the fire. Keep oven gloves, tea towels, and other flammable materials away from the oven. Always turn off the oven when not in use and read the owner’s manual before using the oven.
The general method to cook using an electric oven is:
Check the recipe for an electric oven with recommended time and temperature.
Adjust the temperature knob.
Adjust the time knob.
Preheat the oven.
Use cook methods like bake, broil, grill, and roast.
Take out the cooked food.
The electric oven can be classified as
Conventional oven, and
Convection oven
The convection oven uses a fan to circulate the heat, which is the only difference between them.
An oven that uses electrical energy to heat the food is known as an electric oven. The main components of an electric oven are
Cabinet,
Heating element,
Thermostat,
Timer, and
Power regulating switch.
An electric oven uses electrical energy to cook the food, so all the necessary safety has to be followed while using it. For operating the oven, read the user manual first, then proceed with cooking. The electric ovens are of two types: a conventional oven and a convection oven, which consists of a fan.
Microwave oven
In this module, we will learn the details of a microwave oven. We will learn: What a microwave oven is, How it works, and Use of a microwave oven. Skip to quiz!
Introduction to Microwave Oven
An oven that cooks food using microwave radiation is known as a microwave oven. Microwave ovens heat food using microwaves, a form of electromagnetic radiation similar to radio waves.
A device called a magnetron inside the oven produces microwaves. Microwaves reflect off the metal interior of the oven and cause the water molecules to vibrate in the food. The vibration results in friction between molecules that produce heat which cooks the food.
Generating Microwaves
The magnetron is a high-powered vacuum tube that produces microwaves. Due to the discovery of magnetron, we are now able to use microwave ovens.
A series of operations takes place before the microwaves are generated. For example, the wifi router produces radio waves which are used to connect the mobiles and Laptops. Similarly, a magnetron produces microwaves which are used for cooking food.
The magnetron is a device that is commonly used in different military applications like radars. The desired range and frequencies of waves are obtained by the amount of power supplied to the magnetron. Let us see the properties of microwaves.
Microwaves are a form of electromagnetic radiation. Electromagnetic radiation spans a broad spectrum, and microwaves fall in between the range of 1 gigahertz (GHz) to 300 GHz. The human eye can only see a small portion of this spectrum called visible light, and its range is 400–790 terahertz (THz).
Microwaves have three characteristics that allow them to be used in cooking. The characteristics of microwaves are:
Reflected by metal,
Pass through glass, paper, plastic, and
Some materials and foods absorb them.
The resonance cavity reflects the microwaves produced by the magnetron. A resonance cavity is an electronic device consisting of a space usually enclosed by metallic walls. A microwave is reflected multiple times to achieve a final resonant wave.
A resonant wave in a resonance cavity is oscillating. The oscillating waves with the same amplitude combine to become a giant wave. Recall amplitude is the distance from the centerline (or the still position) to the maximum peak or decline in a wave.
Waves generated can have multiple amplitudes, and the resonance cavity help to generate high amplitude waves. The waves which have a high amplitude possess high energy, so these are suitable for heating.
The standing wave created in a resonance cavity has different intensities at different spots. This creates uneven cooking all around the food, where the waves have higher energy. The waves at these spots cook the food first, and these are known as hotspots.
A rotating plate was invented to overcome this problem. As the microwaves oscillate within the cavity and at specified locations, a rotating plate helps to cook the food evenly. The rotating plates help the food to get heated all round exposed to the waves.
The electronic control is responsible for the microwaves generated by the magnetron. The magnetron is driven by a linear transformer which can be easily switched on or off completely. Recall that the transformer is a device that either increases or decreases the voltage supply in the circuit.
The power level doesn't affect the intensity of the microwave radiation, but the magnetron is cycled on and off every few seconds. This switching helps to achieve the required amount of heat and faster cooking.
Working of a Microwave Oven
Control panels feature an LED, liquid crystal, or vacuum fluorescent display, numeric buttons for entering the cooking time, and power level selection. Some consist of function buttons such as a defrost setting and pre-programmed settings for different food types, such as meat, poultry, vegetables, frozen dinners, and many more.
Power settings are commonly implemented, not by varying the effect but by repeatedly turning the power off and on. The highest power setting thus represents continuous power. For example, A defrost might represent power for two seconds followed by no power for five seconds.
To indicate cooking has been completed, an audible warning such as a bell or a beeper is usually present. Usually, "End" appears on the display of a digital microwave when the food is cooked.
Inside the strong metal box, there is a microwave generator called a magnetron. The magnetron takes electricity from the power outlet and converts it into high-powered microwaves when pressed start. The magnetron sends these waves into the food compartment through a channel called a waveguide.
The food sits on a rotating table, spinning slowly around, so the microwaves cook it evenly. The microwaves bounce back and forth off the reflective metal walls of the food compartment, just like light bounces off a mirror. When the microwaves reach the food, they don't simply bounce off, it penetrates.
As radio waves can pass straight through the walls of your house, so microwaves penetrate inside the food. As microwaves travel through the food, they make the molecules inside it vibrate more quickly. Vibrating molecules generate heat, so the food becomes hotter, and it gets cooked.
Use of a Microwave Oven
Use only microwave-safe cookware specially manufactured for use in the microwave oven. Don't operate a microwave oven if the door does not close firmly or is bent, warped, or damaged. Regularly clean the oven cavity, the outer edge of the cavity, and the door with water and a mild detergent.
Stop using a microwave oven if it continues to operate with the door open. Don't stand directly against an oven (and don't allow children to do this) for long periods while it is operating. Do not heat water or liquids in the microwave oven longer than the recommended time.
The ovens should not be operated when empty and if there is no door seal. Be sure not to use scouring pads, steel wool, or other abrasives to clean the oven. Follow the manufacturer's instruction manual for recommended operating procedures and safety precautions for your oven model.
Each oven has signs on it which material must be used while cooking, and no other material can be used. Metal bowls can’t be used for cooking as the radiation penetrates through them. While using metal bowls with sharp edges may cause sparks and flashes.
High amounts of radiation exposure from the oven can cause skin burns. Overheating of the food may be quickly done in the oven so that handling issues may be present. Closed items, such as eggs, canexplode when heated in a microwave oven due to the increased pressure from steam.
An oven that cooks food using microwaves is known as a microwave oven. A magnetron generates microwaves, and the resonance cavity helps create longer waves that cook food. Microwave ovens are hazardous when not used in prescribed ways.
Question #1: An electric oven uses electrical energy, and it converts the electricity into heat using _____.
Heating element
Door
Convection Fan
Cabinet
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Answer: Heating element
An electric oven uses electrical energy, and it converts the electricity into heat using heating elements.
Question #2: The heating element in an electric oven converts electrical energy into heat through the process of ______
Conductance
Current
Resistance
Heating
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Answer: Resistance
The heating element in an electric oven converts electrical energy into heat through the process of resistance.
Question #3: The electric oven comprises of (Select all that apply)
Stove
Cabinet
Battery
Thermostat
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Answer: Cabinet
Thermostat
The electric oven comprises of a
Cabinet,
Heating element,
Thermostat,
Timer, and
Power regulating switch.
Question #4: In an electric oven metal box body is composed of
Outer shell
Middle layer
Inner container
All of the above
Scroll down for the answer...
Answer: All of the above
In an electric oven the metal box body is composed of
an outer shell,
a middle layer, and
an inner container.
Question #5: The broil element is typically found at the top of the oven cavity and provides ______ heat to the top of food for broiling.
Continuous
Transfer
No
Direct
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Answer: Direct
The broil element is typically found at the top of the oven cavity. It provides direct heat to the top of food for broiling.
Question #6: The thermostat is connected to a capillary tube which consists of ____.
Mercury
Gas
Air
Water
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Answer: Gas
The thermostat is connected to a capillary tube which consists of gas
Question #7: When the user sets a timer and required temperature, then which elements get heated?
Thermostat
Oven cavity
Convection Fan
Bake and broil element
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Answer: Bake and broil element
When the user provides the temperature and time, the control board sends the 120V to the broil and bake heating element.
Question #8: Always turn off the oven when not in use. (Select true or false)
True
False
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Answer: True
Always turn off the oven when not in use. Read the owner’s manual before using the oven.
Question #9: Never use ____ on a kitchen grease fire; use a wet cloth to extinguish the fire.
Air
Water
Utensils
Fan
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Answer: Water
Make sure to keep the oven clean from grease and splatters of food that can catch fire. Never use water on a kitchen grease fire; use a wet cloth to extinguish the fire.
Question #10: The main difference between a conventional oven and a convection oven is a ____.
Bake element
Heater
Fan
Tray
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Answer: Fan
The main difference between a conventional oven and a convection oven is the fan. A convection fan helps in cooking the food evenly.
Question #11: Which device is responsible to produce microwaves inside the microwave oven?
Thermostat
Electron
Magnetron
Light bulb
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Answer: Magnetron
A device called a magnetron inside the oven produces microwaves in the microwave oven.
Question #12: The desired range and frequencies of waves are obtained by controlling the _____ supplied to the magnetron.
Power
Light
Coil
Water
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Answer: Power
The desired range and frequencies of waves are obtained by controlling the power supplied to the magnetron
Question #13: The characteristics of microwaves are: (Select all that apply)
Reflected by metal
Switch on the light
Some materials and foods absorb them
Provide X-ray images
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Answer: Reflected by metal
Some materials and foods absorb them
The characteristics of microwaves are:
Reflected by metal,
Pass through glass, paper, plastic, and
Some materials and foods absorb them.
Question #14: In a resonance cavity, a microwave is ______ multiple times to achieve a final resonant wave.
Refracted
Stopped
Transmitted
Reflected
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Answer: Reflected
In a resonance cavity, a microwave is reflected multiple times to achieve a final resonant wave.
Question #15: As the microwaves oscillate within the cavity and at specified locations, a rotating plate helps to cook the food _____.
Partially
Evenly
At required places
One side
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Answer: Evenly
As the microwaves oscillate within the cavity and at specified locations, a rotating plate helps to cook the food evenly.
Question #16: Closed items, such as eggs, can ______ when heated in a microwave oven due to the increased pressure from steam.
Explode
Break
Cook easily
Damage
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Answer: Explode
Closed items, such as eggs, can explode when heated in a microwave oven due to the increased pressure from steam.