Energy transfers
8
K
464 © Pearson
3 The changes in the air temperature inside the house
would be closer to the outside air temperatures, as
there is not as much thermal mass to store energy.
4 a warmer during the day than at night
b The slab will warm up when the Sun shines on
it during the day. At night the slab will be warmer
than the air temperature inside the house, so it will
emit energy and help to keep the air warm.
c Energy can escape through the window more
easily than through the walls, so the small size of
the window helps to reduce heat transfers. The Sun
never shines on the north side of the house so it is
no use for absorbing energy.
5 The Sun is higher in the sky in summer, so the
overhanging eaves will prevent the Sun shining into
the house. The floor slab will remain cooler and so
it will absorb energy from warm air and help to keep
the house cool.
8Kd Power and efficiency
Student Book
1: 8Kd Power and efficiency
1 a any three heating appliances, e.g. kettle,
cooker, oven, tumble dryer, hairdryer
b any three appliances whose primary purpose
is not heating, e.g. TV, DVD player, radio, fridge,
computer, electric drill, lawnmower
2 a 10 000 W b 10 kW
3 a 3 kJ or 3000 J
b It does not need to heat as much water as
quickly.
4 a efficiency = useful energy ÷ total energy ×
100% = 9 ÷ 20 × 100% = 45%
b Students’ own Sankey diagrams with 20J
on the left-hand side of the arrow, ‘9 J light’ as an
arrow approximately one-third the size of the main
arrow on the right, ‘11 J transferred by heating’ as
an arrow approximately two-thirds the size of the
main arrow on the right; arrows should be labelled
5 a 80% of 200 kJ = 160 kJ
b Students’ own Sankey diagrams with ‘useful
energy’ arrow approximately four times the width
of ‘wasted energy’ arrow, both on the right; labelled
with ‘energy used by a kettle’, ‘useful energy stored
in hot water’ and ‘wasted energy stored in kettle
and surroundings’
c Kettles have lids/are enclosed so less energy
is transferred from the water by evaporation and
convection while the water is heating up.
2: 8Kd Managing disasters (STEM)
1 Answers could include:
a Which parts of a country/which towns or
villages have been damaged/flooded etc. Whether
roads in the area are open or blocked.
b How many emergency and medical workers
the country can provide. How much equipment for
rescuing people and treating the injured they have.
What extra help they need. The best way of getting
more people and supplies to the disaster areas.
c Detailed reports (by mobile phone, Internet
or radio) of damage in the area. Reports of people
missing (who need to be found).
2 Sleeping in tents will help to keep them warm at
night. Without tents, many people would die from
the cold.
3 a Answers could include: providing lighting or
heating or cooling in hospital and other temporary
buildings, operating other medical equipment,
operating computers and communications
equipment.
b A more efficient generator will need less fuel
to produce a certain amount of electricity, meaning
that less fuel has to be taken to the disaster area.
4 The most likely two renewable resources are
wind and solar power. She would need to find out
how windy the place is, and how much sunshine it
gets at that time of year.
5 a Adding insulation to the cool box reduces the
rate at which the contents will warm up. This means
that less energy will be needed to keep the inside
cool, so the box is more efficient.
b The cool box would be useful if vaccines have
to be taken to remote areas in a small vehicle or
on foot. The solar panel is required to power the
cool box or refrigerator as there is unlikely to be a
reliable electricity supply in the disaster area.
Activity
a a Phi Phi is an island, so road transport is not
an option. It is hot all year round (between approx.
22°C and 33°C all year round). There is some
rainfall Dec-Mar, and heavy rainfall in the other
months of the year.
b Lapu is in the Gorkha province of Nepal. Roads,
where they exist, are stony tracks on steep
mountainsides. Minimum temperatures vary from
8°C in December and January to 25°C in June-
August. Maximum temperatures vary between 22°C
and 35°C. Rainfall is low from October to April, and
high in the remaining months.
b People could include: search and rescues
teams; engineers to supervise digging people out
of ruined buildings or to repair bridges and roads;
doctors and nurses; search and rescue teams,
people to make records of people saved and people
still missing, to give out tents, food and water.
Equipment could include: search equipment such
as infrared cameras; digging and engineering
equipment such as bulldozers, diggers, shovels;
shelters, such as tents or other temporary buildings;
computers; medical equipment.