energy transfer by heating

Question 1

which materials conduct best

Answer 1

metals conduct better than non metals
copper conducts better than steel
glass conducts better than wood

Question 2

how to do you compare conductors in a practical

Answer 2

rods same width and length
rods coated with thin layer of wax on one end
wax melts fastest on best conductor

Question 3

the greater the thermal conductivity of an object…

Answer 3

the more energy per second it transfers by conduction

Question 4

what is thermal conductivity

Answer 4

a measure of how well a material conducts energy when it is heated

Question 5

The energy transfer per second through a layer of insulating material depends on

Answer 5

the temperature difference across the material
the thickness of the material
the thermal conductivity of the material

Question 6

what do good insulators need to have

Answer 6

• a low thermal conductivity
• as thick as possible

Question 7

What kind of material makes a good insulator

Answer 7

• non metals
• wool and fibreglass

Question 8

the higher the temperature of an object…

Answer 8

the more infrared radiation it emits in a given time

Question 9

what do all objects emit and absorb

Answer 9

infrared radiation

Question 10

how can you conduct a practical to detect infrared radiation

Answer 10

• glass prism splits a narrow beam of white light into the colours of the spectrum
• thermometer reading rises when placed just beyond red part of spectrum because some of the IR in the beam goes there

Question 11

a body at a constant temperature …

Answer 11

emits infrared radiation at the same rate it absorbs it

Question 12

what is a black body

Answer 12

• an object that absorbs all radiation that hits it (doesn’t reflect or transmit any radiation)
• best possible emitter
• emits black body radiation

Question 13

an object that has a constant temperature emits radiation across

Answer 13

a continuous range of
wavelengths

Question 14

if the temperature of the object is increased

Answer 14

the intensity of the radiation it emits is greater at every wavelength

Question 15

the shorter the wavelength of the radiation

Answer 15

the greater the increase in intensity in that wavelength. so peak intensity is at a shorter wavelength at a higher temperature than in was at the lower temperature.

Question 16

if an object has a constant temperature, the objects emits infrared radiation at

Answer 16

the same rate it absorbs it

Question 17

a light coloured, shiny blanket emits a lot less radiation than a dark, matt surface. True or False?

Answer 17

True - this keeps the patient warm

Question 18

what factors affect the temperature of the earth?

Answer 18

the rate that light and infrared from the sun are:
- reflected back into space or absorbed by the earths atmosphere or surface
- emitted from the earths surface and atmosphere into space

Question 19

what wavelength do greenhouse gases absorb

Answer 19

longer wavelength reflecting off the earths surface

Question 20

what factors does temperature rise depend on

Answer 20

• amount of energy supplied to it
• mass of the substance
• what the substance is

Question 21

what is the definition of specific heat capacity

Answer 21

the energy needed to raise the temperature of 1kg of a substance by 1 degree

Question 22

what is the equation for specific heat capacity

Answer 22

for a known change of temperature of a known mass of a substance
energy transferred = mass * shc * temperature change

Question 23

what are the units for shc

Answer 23

J/kg’C

Question 24

the energy transferred to the substance increases the…

Answer 24

thermal energy store of the substance by an equal amount

Question 25

how would you conduct a practical to measure specific heat capacity

Answer 25

1 - measure mass of a metal block
- then heat it by connecting to a heater
- use joulemeter to measure energy supplied to the block
- use thermometer to measure temperature rise
- put into equation
2 - replace block with an equal mass of water and measure temp rise of the water when the same amount of energy is supplied to it by the heater
- shows aluminium heats up faster than water

Question 26

how do storage heaters work

Answer 26

• uses electricity at night (off peak) to heat special bricks or concrete blocks in the heater
• energy transfer from the bricks keeps the room warm
• bricks have a high shc so store lots of energy. Warm up slowly when the heater is on and cool down slowly when it is off.

Question 27

why would you want to reduce the transfer of energy to the surroundings

Answer 27

• too prevent heat from escaping
• to reduce heating heating bills

Question 28

how would you reduce the rate of energy transfers at home

Answer 28

• loft insulation such as fibreglass (is a good insulator)
  air between fibres reduces rate by conduction
• cavity wall insulation
  space between two layers of brick filled
  traps air in small pockets, reduces rate by conduction
• aluminium foil between radiator panel and the wall
  reflects radiation away from wall, reduces rate by radiation
• double glazed windows have 2 glass panes with dry air or a vacuum between panes
  reduces rate by conduction and convection
• external walls have thicker bricks and a lower thermal conductivity

Question 29

why are solar panels useful and how do they work

Answer 29

• electricity or gas can be expensive
• absorb infrared radiation from the sun to generate electricity or heat water directly (solar cell panels and solar heating panels)
• in northern hemisphere, roof that faces south for more light from the sun