P1 Revision

P1: Energy
for the
Home…read more

P1a: Heating Houses…read more

Basics:
· For warm bodies, the rate of cooling depends on the temperature
difference compared to their surroundings
· Temperature is represented by colour in a
thermogram (hottest parts: white/red. Coolest
parts: black/blue)
· Energy, in the form of heat, flows from a warmer to a colder body.
When energy flows away from a warm object, the temperature of
that object decreases.
· Temperature is a measurement of hotness on an arbitrary or
chosen scale
· Temperature is a measurement of the average kinetic energy of
particles
· Heat is a measurement of energy and is measured in Joules (J)
· The energy needed to change the temperature of a body depends
on its mass, its material and the temperature change…read more

Specific Heat Capacity:
· All objects have a property called Specific Heat Capacity
(SHC) which is the energy needed to raise the
temperature of 1kg by 1°C and is measured in joules per
kilogram degree Celsius (J/kg °C). It differs for different
materials.
· When an object is heated and its temperature rises,
energy is transferred
E
· Water has an SHC of 4200
· Equation: m SHC t
Energy transferred = mass x SHC x temp. change
· E.g. Calculate the energy transferred when 30kg of
water cools from 25°C to 5°C...
Energy transferred = 30 x 4200 x 20
= 252,0000J or 2520kJ…read more

Specific Latent Heat:
· Specific Latent Heat (SLH) is the energy needed to melt or
boil 1kg of the material and is measured in joules per
kilogram (J/kg) and differs for different materials as well as
each change of state.
· When an object changes state, energy is transferred, but the
temperature remains constant. This is because the energy is
needed to break the bonds that hold the molecules together.
· Water has SLH of 340,000 E
· Equation:
m SLH
energy transferred = mass x SLH
· E.g. Calculate the energy transferred when 2.5kg of water
changes from solid to liquid at 0°C.
energy transferred = 2.5 x 340,000
= 850,000J or 850kJ…read more

P1b: Keeping Homes
Warm…read more