8. (a) What is heat? Explain how heat is transferred in a solid - Leaving Cert Physics - Question 8 - 2010

Heat transfer in solids occurs primarily through conduction. In this process, atoms in a solid material vibrate and collide with neighboring atoms, transferring energy from the warmer areas to cooler areas. When atoms are in contact, the vibrations transfer energy efficiently, allowing heat to flow through the material.

One way to carry out this comparison is to use a setup with several rods made of different materials (e.g., copper, aluminum, wood) of the same length and thickness. Each rod would have one end heated, and the temperature at the opposite end would be measured over time.

• Apparatus: Rods of different materials, heat source, thermometer.
• Procedure: Heat one end of each rod uniformly and measure the time taken for the temperature at the other end to rise a certain degree.
• Observation: Record which material conducts heat faster by noting which rod reaches the target temperature first. This will illustrate varying rates of heat transfer among different solids.

The U-value, or thermal transmittance, measures the rate of heat transfer through a building element, such as walls, roofs, or windows. It is expressed in watts per square meter Kelvin (W/m²·K), indicating how much heat will pass through a square meter of the element for each degree of temperature difference on either side. A lower U-value signifies better insulation properties.

The U-value can be reduced by improving insulation. This can be achieved through several methods: adding thicker insulation material in walls, installing double or triple glazed windows, or using insulating materials like foam or fiberglass. Each of these methods helps to slow the rate of heat transfer, enhancing the energy efficiency of the building.

The sun's energy is primarily transferred to the solar collector through radiation. The solar collector absorbs sunlight and converts it into heat, which is then used to warm the water circulating through the system.

A solar collector is typically painted black because black surfaces absorb more heat from sunlight than lighter colors. This maximizes the efficiency of heat absorption and ensures that the collector gathers the greatest possible amount of solar energy.

Heat is transferred from the solar collector to the hot water tank through a circulating fluid (usually water or a glycol solution). As the solar collector heats this fluid, it is pumped through pipes to the hot water tank, transferring thermal energy.

The heating coil is placed near the bottom of the hot water tank because hot water rises. By heating the water at the bottom, the entire tank can reach a uniform temperature efficiently, with heated water naturally rising to the top for immediate use.

An advantage of a solar heating system is its sustainability; it utilizes renewable solar energy, reducing dependence on fossil fuels and lowering energy bills. A disadvantage is that its efficiency can be significantly affected by weather conditions, as cloudy days can reduce energy production.