The Physics Question Bank

A heat wave is a period of unusually hot weather that lasts for several days. It is not just “a hot day”. A heat wave happens when the atmosphere allows heat to build up over time.

The main source of the energy is the Sun. The Sun transfers energy to the Earth by radiation. This radiation travels through space and reaches the ground, buildings, roads and water.

During the day, surfaces such as tarmac, concrete, brick and soil absorb energy from the Sun. Their particles gain energy and vibrate more. This increases the internal energy of the surfaces, so their temperature rises.

These hot surfaces then warm the air above them. Energy is transferred from the ground to the air by conduction, infrared radiation and convection. As the air gains energy, its temperature increases.

In many heat waves, a large area of high pressure sits over the region. This is important because high pressure air tends to sink. As the air sinks, it is compressed and warms up. It also acts like a lid, making it harder for warm air near the ground to rise and escape.

This can create what is sometimes called a heat dome. The hot air becomes trapped close to the ground. Each day, the Sun adds more energy, but the heat is not removed quickly enough. The temperature rises day after day.

Clear skies make the effect stronger. With fewer clouds, more radiation from the Sun reaches the ground. This means more energy is absorbed during the day.

Light winds can also make a heat wave worse. If the air is not moving much, cooler air is not brought in from elsewhere. The same warm air stays over the same place and continues to heat up.

Nights are important too. During a heat wave, the ground and buildings may not lose enough energy overnight. If the night stays warm, the next day starts from a higher temperature. After several days, the heat builds up even more.

Cities can become especially hot because of the urban heat island effect. Dark roads, roofs and buildings absorb lots of radiation from the Sun. Concrete, brick and tarmac store thermal energy during the day and release it slowly at night. This means cities often stay warmer than the countryside.

A heat wave is usually caused by several factors working together:

strong sunlight

clear skies

high pressure

sinking air

light winds

hot surfaces absorbing radiation

less cooling overnight

The energy transfer can be written simply like this:

energy from the Sun → absorbed by the ground and buildings → transferred to the air → air temperature increases

A strong GCSE explanation would be:

A heat wave forms when energy from the Sun is absorbed by the ground, roads and buildings over several days. These surfaces heat up and transfer energy to the air, increasing the air temperature. A high pressure system can trap warm air near the ground, like a lid. Clear skies allow more solar radiation to reach the surface, and light winds mean the hot air is not moved away. If nights stay warm, less energy is lost, so the heat builds up day after day.

This is a useful GCSE Physics example because it links weather to energy transfer. A heat wave is not just caused by “hot weather”. It happens when energy enters an area faster than it is transferred away.