How Does a Microwave Oven Work?
A microwave oven heats food with invisible radio waves that make the water inside the food move and warm up. Here is how a microwave oven works, step by step, what each part does, and why grill and convection models can brown and bake while a basic solo oven cannot.
Updated 11 November 2026
The working principle of a microwave oven in simple words
Food contains water. Water molecules have a positive end and a negative end. When microwaves pass through food, their electric field flips billions of times a second, and the water molecules keep turning to follow it. This rubbing and turning creates heat inside the food itself.
That is why a microwave is fast: it heats the outer few centimetres of the food directly, and the heat then spreads inwards. A pot on a stove has to heat the pot first and then the food from the outside. It is also why dry things like an empty plate stay fairly cool, while the curry on the plate gets hot.
What frequency does a microwave oven use?
Home microwave ovens work at about 2.45 GHz (about 2.45 billion waves per second). The wavelength is about 12 cm. This frequency is set aside around the world for ovens and other heating uses, and it is good at heating water without needing huge power.
Microwaves are non-ionising radiation, the same broad family as radio and Wi-Fi signals. They heat food, but they do not make it radioactive, and they stop the instant the oven switches off. Our microwave safety guide explains the health side in more detail.
Main parts of a microwave oven and their functions
- Magnetron: the heart of the oven. It turns electricity into microwaves.
- High-voltage transformer, capacitor and diode: they raise the household 220 V to the few thousand volts the magnetron needs.
- Waveguide: a metal channel that carries the waves from the magnetron into the cooking box.
- Cavity: the metal cooking box. Its metal walls bounce the waves around so they reach the food from all sides.
- Turntable and motor: the glass plate turns the food so it heats more evenly.
- Door with metal mesh: the small holes are much smaller than the 12 cm waves, so the waves cannot pass, but light can, so you can see the food.
- Door switches (interlocks): they cut the power the moment the door opens.
- Control panel and timer: knobs on manual models like the Homage HMSO-2020B 20 Litre Solo Microwave Oven, a touch panel on digital models like the Dawlance DW-390 S 23 Litre Solo Microwave Oven.
- Cooling fan, lamp and fuse: they keep the parts cool, light the inside and protect the circuit.
What happens when you press Start
- The door switches confirm the door is shut.
- The timer, fan, lamp and turntable motor switch on.
- The transformer and capacitor build up high voltage, and the magnetron starts making microwaves.
- The waves travel down the waveguide and fill the cavity.
- Water, fat and sugar in the food absorb the waves and heat up.
- When the time ends or the door opens, the magnetron stops at once.
Lower power levels do not make weaker waves. On most ovens the magnetron simply switches on and off in cycles. You can often hear the hum change. An inverter microwave oven instead delivers a steady lower power, which is gentler for defrosting.
How a grill microwave and a convection microwave work
A grill microwave adds a heating element at the top of the cavity. It works like a small toaster grill and browns the surface by direct heat. In combi mode the oven switches between microwave and grill, so the food cooks inside and browns outside together. See the grill microwave oven range.
A convection microwave adds a heater and a fan at the back. The fan moves hot air around the cavity, just like an electric baking oven, so it can bake cake and bread at a set temperature such as 180 °C. Models such as the Kenwood MWP29.000BK 30 Litre Convection Microwave Oven and PEL PMO-26 Kitchen Pro CAF 26 Litre Air Fryer Microwave Oven work this way. An air fryer microwave uses the same idea with faster air for crisp food.
The solo vs grill vs convection comparison shows which type suits your cooking.
Why metal sparks and why food heats unevenly
Thin or pointed metal, such as foil edges, forks or the gold rim on a plate, gathers the electric charge and can spark. That is why steel dishes are kept out of microwave mode. The cavity walls are metal too, but they are smooth, thick and designed for it.
Microwaves form hot and cold spots inside the box. The turntable and stirring halfway help even this out. Frozen food is tricky because ice absorbs microwaves much less than water, so the thawed edges race ahead. This is why the defrost setting pauses often to let heat spread.
How many types of microwave ovens are there?
All microwave ovens use the same magnetron, but they add different heaters on top. In Pakistan you will find six main types:
- Solo: microwave only, for reheating, defrosting and simple cooking. See Solo Microwave Oven Price in Pakistan.
- Grill: adds a top heater for browning, toast and tikka.
- Convection: adds a fan heater, so it can bake at a set temperature.
- Air fryer microwave: convection with faster air for crisp fries and wings, for example the PEL PMO-30 Kitchen Pro ICAF 30 Litre Air Fryer Microwave Oven.
- Built-in: fits into a kitchen cabinet; see Built-in Microwave Oven Price in Pakistan.
- Inverter: gives steady low power instead of switching on and off, like the Dawlance DW-MD20 INV 20 Litre Solo Microwave Oven.
Manual models use knobs and digital models use a touch panel and auto menus; both heat food the same way.
Who invented the microwave oven?
The microwave oven was invented by Percy Spencer, an American engineer working on radar in the 1940s. He noticed that a chocolate bar in his pocket melted near a working magnetron, and he then tested popcorn and an egg. The first commercial microwave ovens were huge and were made for restaurants. Small countertop models for homes became common from the 1970s onwards, and today they are a standard appliance in Pakistani kitchens.
What this means when you buy a microwave
- Microwave power (watts) decides how fast food heats. 700 W suits reheating; 900 W and above cooks faster. See our microwave electricity guide.
- Capacity (litres) decides the size of dish that fits. See the microwave size guide.
- The type (solo, grill, convection or air fry) decides what the oven can cook, not just heat.
Browse all models on the Microwave Oven Price in Pakistan page, where live prices start from Rs 10,000.
When was the microwave invented? A short timeline
- 1945: American engineer Percy Spencer noticed that radar equipment melted a sweet in his pocket and found that microwaves could heat food.
- 1947: the first commercial microwave oven was sold. It was almost as tall as a person and was used in restaurants.
- Late 1960s: the first countertop microwave ovens for homes arrived.
- Today: microwaves are smaller and add grill, convection, air fry and inverter control.
The basic idea has not changed: a magnetron makes microwaves that heat the water in food.
