Insolation and factors affecting it

Dense clouds and dust block radiation, and oblique rays spread energy. All three reduce insolation.

Direct rays concentrate energy, clear sky blocks less, and long day increases duration. This is a high-insolation combination.

Solar constant is related to the rate of received solar energy. Its change affects incoming solar energy.

Albedo is the fraction of incoming insolation reflected by a surface. When albedo increases, the surface reflects more radiation, so it absorbs less insolation. Option B is the opposite relationship: greater reflection does not mean greater absorption. Exam tip: in simple terms, the absorbed fraction is \(1-\text{albedo}\).

In the tropics, the Sun's altitude remains high and rays are relatively direct. This is a main reason for high insolation.

Dark surfaces have low albedo and high absorption. With fewer green areas, cooling processes also reduce.

Clouds can send solar radiation back and a high-albedo surface does the same. Thus both can reduce heating.

A surface’s colour is related to how much incoming solar radiation it reflects and absorbs. A black surface generally has a lower albedo, meaning that it reflects a smaller proportion of the received energy. It therefore absorbs more energy and can become hotter when both cars receive similar sunlight. A white surface generally has a higher albedo and reflects more radiation, so it often warms less under the same conditions. The exact temperature also depends on material, ventilation, and other factors.

Option A is correct because greater absorption provides more energy for heating the black car. Option B reverses the usual relation between black and white surfaces. Options C and D are unrelated to the way surface colour affects heating: a car cannot change day length, and a white car cannot block the Sun. The question tests absorption and albedo.

When a surface has high heat capacity, a large amount of received energy is needed to raise its temperature, so it warms slowly. Water is a key example: for the same energy input, its temperature rises less than that of land. Low albedo would increase energy absorption, so it does not best explain a small temperature rise. Exam tip: distinguish between receiving energy and the resulting temperature increase by considering heat capacity.

From morning to noon, the Sun rises higher, increasing the ray angle. Therefore energy per unit area increases.

The direct answer is A: the Sun’s altitude decreases and its rays become more oblique. Around noon, the Sun is highest in the sky for that day. After noon it appears lower toward the horizon. Lower altitude makes sunlight travel through a longer atmospheric path, and oblique rays spread the same energy over a larger surface area. Thus the intensity of insolation decreases, although daylight continues for some time. Option A is correct for both reasons. Option B is wrong because the Sun continues radiating energy constantly; it does not stop after noon. Option C is wrong because afternoon does not immediately become night. Option D is wrong because the atmosphere remains present; it is not removed after noon. A useful distinction is that maximum daily heating may occur somewhat after noon because the ground and air respond slowly, but the incoming solar angle begins decreasing after noon. Remember: after noon, lower Sun, longer path, weaker direct insolation.

Earth's spherical shape causes ray angle to change at different latitudes. This is a major basis of unequal insolation.

Higher Sun altitude means more direct rays. Therefore annual insolation can be high in that region.

Very high humidity means that there is more water vapour in the atmosphere. Water vapour absorbs part of the incoming solar radiation, especially at certain longer wavelengths, so the amount of insolation reaching Earth’s surface can decrease or change. Earth’s rotation affects the day–night cycle, but it is not altered by humidity. Exam tip: water vapour, dust and clouds can affect insolation through absorption, scattering or reflection.

In reflection energy goes back, while in absorption the surface takes energy. Albedo is related to reflection.

The direct answer is A: the ground remains cool under dense trees. Surface cover means material such as vegetation, snow, soil or water lying over the ground. A dense tree canopy intercepts, reflects and absorbs much of the incoming sunlight, so fewer direct rays reach the soil. Trees can also cool nearby ground through shade and evapotranspiration. Option A is correct because it shows a local difference caused directly by vegetation cover. Option B is wrong because Earth’s revolution is a planetary movement, not an example of local surface cover. Option C is wrong because equal day and night at an equinox results mainly from Earth’s position and axial geometry. Option D is wrong because perihelion concerns Earth’s orbital distance from the Sun, not the cover on a particular surface. The key is to ask what blocks or changes radiation at the local ground: a canopy does. Memory cue: shade is a surface-cover effect; orbit is not.

A darker surface has lower albedo and absorbs more energy. So heating can increase after snow melts.

The sea heats slowly and can moderate coastal temperature. Thus even with similar insolation, coastal temperature rises slowly.

The zone of vertical sun rays shifts between the Tropics of Cancer and Capricorn. This changes insolation by latitude.

Even with high insolation, high albedo or high heat capacity can limit temperature rise. So check surface properties.

Direct answer: Option A, the energy absorbed by the surface will decrease. Heat balance means the balance between incoming solar energy, reflected energy, absorbed energy, and energy released back from Earth. If a larger share is reflected, that share does not enter the surface. Step by step: solar energy arrives; some is reflected; the remaining part is absorbed; therefore, when reflection increases, the absorbed part decreases, and the surface gains less heat. Option A is correct because it states exactly this relationship. Option B is wrong because reflection means the surface does not take all the energy. Option C is irrelevant: reflection does not change the length of day. Option D is wrong: surface reflection cannot move the Sun closer to Earth. Exam cue: more reflection means higher albedo, less absorption, and usually less surface warming.

Angle of rays is a broad factor and albedo is a local surface factor. Together they affect heating.

A long day and clear sky bring more energy, and low albedo increases absorption. This is a good combination for higher heating.

Insolation is affected by many factors. So decide by combining angle, day duration, clouds, dust, and surface properties.

Total insolation is not determined by day length alone. A long day increases the duration of incoming solar energy, but oblique rays spread the same energy over a larger area and travel through more atmosphere, so energy received per unit area may be lower. Option A considers only one factor, while option B incorrectly treats insolation as zero. Exam tip: In insolation questions, consider both duration of daylight and the angle of solar rays together.