Chapter 2: Energy transfer by heating

Question 1

Energy transfer by conduction

Answer 1

• Metals are the best conductors of energy
• Non-metal materials such as wool and fibreglass are the best insulators
• The higher the thermal conductivity of a material, the higher the rate of energy transfer through it
• The thicker a layer of insulating material, the lower the rate of energy through it.

Question 2

Infrared radiation

Answer 2

• All objects emit and absorb infrared radiation
• The hotter an object is, the more infrared radiation it emits in a given time
• Blackbody radiation is radiation emitted by a body that absorbs all the radiation incident on it. A black body is a body that absorb all radiation of all wavelengths that is emitted onto it, none of it is reflected. A black body is theoretical, and things only come close to them, like black holes.

Question 3

Infrared radiation (higher tier)

Answer 3

• The temperature of an object increases if it absorbs more radiation than it emits
• The earth’s temperature depends on a lot of factors, including the absorption of infrared radiation from the sun, and the emission of radiation from the Earth’s surface and atmosphere.
• Light, shiny objects emit much less infrared radiation than dark, matte objects. Therefore rescue teams use shiny blankets to keep accident survivors warm.

Question 4

Specific heat capacity

Answer 4

• The specific heat capacity of a substance is the amount of energy needed to the change the temperature of one kilo by one degrees.

• The equation is:
Energy transferred, ΔE= mass, m x specific heat capacity, c x temperature change, Δθ

• The greater the mass of an object, the more slowly its temperature increases when it is heated

• To find the specific heat capacity of a substance, use a joulemeter and a thermometer to measure energy transferred and change in temp for a measured mass, the use:
C = ΔE / m x Δθ

Question 5

Heating and insulating buildings

Answer 5

• Electric and/or gas heaters and gas or oil-fired central heating or solid-fuel ovens are used to heat houses.
• The rate of energy transfer from house can be reduced by using:

  o	Loft insulation
  o	Cavity wall insulation
  o	Double-glazed windows
  o	Aluminium, foil behind thicker bricks and lower thermal conductivity

• Cavity wall insulation is insulation material that is used to fill the cavity between two brick layers of an external house wall