Chapter 10

• Temperature is a physical quantity that measures how hot or cold an object is
• The S.I. unit of temperature is Kelvin (K)
• Density is the mass of a substance per unit volume
• Touch cannot be used to determine whether an object is hot or cold as it differs from person to person
• Lowest temperature is 0K, absolute zero
• Thermometer is used to measure temperature
• heat energy is transferred from a hotter region to a cooler region by conduction, convection, and radiation
• Transfer of heat energy stop when both are of the same temperature
• Gases expand the most as they have weak forces of attraction
• When something expands, volume increases while mass stays unchanged, density would decrease
• When something contracts, volume decrease while mass stays unchanged, density would increase.
• persistent expansion of inside of glass will cause it to break due to unequal expansion
• bimetallic strip made into coil (thermometer), as temp changes unequal expansion/contraction causes it to squeeze and its pointer moves over scale to show temperature
• Bimetallic strip is made of brass and iron/steel
• Bimetallic strip bends when it is heated/cooled because brass expands/contracts faster then iron/steel
• Bimetallic strips are used in thermostats to regulate temperature and fire alarms
• Answering structure:

  1. Its heated
  2. Brass expands faster than iron
  3. Bends upwards/downwards and toward/away from the contact
  4. Circuit is opened/closed

  Vice versa for cooling
• Pipes carry hot water have expansion loops so when it expands it won't tighten and break.
• Conduction is the transfer of heat energy through a material without obvious movement of the object.
• Metals are good conductors because they contain many free electrons that move easily between atoms.
• Thermal conductivity is how well a material conducts heat energy
• Heat transfer BY CONDUCTION will occur faster in materials with high thermal conductivity
• The greater the surface area exposed to the hotter side, the more rapid the rate of conduction
• When two objects at different temperatures come into contact, there is always some heat transferred until equal temperature
• Convection occurs as movements from hot to cool places due to different densities
• When answering convection questions, state that it forms a convection current.
• Convection (warm):

  Air gains heat and expands, volume increases and density decreases. Warm air will be less dense than cooler air and rise up. Cooler denser air from above replaces it, sets up a convection current so that.. (STATE REASON like the food in the container can be warmed thoroughly)
• DIFFERENCE BETWEEN CONDUCTION AND CONVECTION

  • occurs mainly in solids/ occurs in fluids
  • Heat flows any direction/ heat flows upward
  • Heat transferred without object moving/ hot fluid move to transfer energy
• Radiation is the transfer of heat energy without a medium
• Radiation is the only heat transfer method that can occur in vacuum
• Radiation travels in form of waves
• When object is warmer than surrounding, radiates heat energy rather than absorbing it
• Good absorbers when describing an object that is originally cooler than surroundings. Good radiators when object is warmer than surroundings
• (Radiation)Surface area

  The greater Surface are, faster rate of heat radiation absorption
• (Radiation)Temperature

  The greater difference in temperature between object and surrounding where object is warmer, faster rate of radiation
• (Radiation) colour and texture

  Rough and black absorb/radiate heat faster than smooth, white ones