Transcript J-Home_Heating_Multiple_Choice_Questions

Energy Use
at Home
Home Heating
Multiple-Choice Questions
(Junior Science Level)
Physics and Astronomy Outreach Program at the University of British Columbia
Question 1
Home
Heating
You come into a cold room and switch on the space
heater. Which statement is true during the time
when the temperature in the room is rising?
A. The power delivered by the heater is larger
than the heat lost from the room.
B. The power delivered by the heater is smaller
than the heat lost from the room.
C. The power delivered by the heater is the same
as the heat lost from the room.
Physics and Astronomy Outreach Program at the University of British Columbia
Question 1 Answer
Home
Heating
You come into a cold room and switch on the space
heater. Which statement is true during the time
when the temperature in the room is rising?
A. The power delivered by the heater is larger
than the heat lost from the room.
B. The power delivered by the heater is smaller
than the heat lost from the room.
C. The power delivered by the heater is the same
as the heat lost from the room.
Physics and Astronomy Outreach Program at the University of British Columbia
Home
Heating
Question 2
On a cold, still day, you are trying to determine the
energy balance of your home. Which of these
assumptions of energy flow is unreasonable?
C
A
Energy Flow In
(from sunshine)
B
Energy Flow In
(“fuel”)
House
(heat loss to cold air
through conduction)
D
Heat
generated
inside house
(heat loss to the air
through convection)
E
(heat loss to cold air
through radiation)
Physics and Astronomy Outreach Program at the University of British Columbia
Question 2 Answer
Home
Heating
On a cold, still day, you are trying to determine the
energy balance of your home. Which of these
assumptions of energy flow is unreasonable?
C
A
Energy Flow In
(from sunshine)
B
Energy Flow In
(“fuel”)
House
(heat loss to cold air
through conduction)
D
Heat
generated
inside house
(heat loss to the air
through convection)
E
(heat loss to cold air
through radiation)
Physics and Astronomy Outreach Program at the University of British Columbia
Question 2 Solution
Home
Heating
The sun’s radiation energy will enter the house
through the window. The furnace will heat up the
house, as will many appliances within the house
(lights, people).
As the house warms up, heat will be lost to the air
through radiation and convection, not conduction.
This is because the heat is lost to a mobile fluid (the
air), not a solid, even though the mobile fluid is still. If
it were a windy day, it would be forced convection.
Physics and Astronomy Outreach Program at the University of British Columbia
Question 3
Home
Heating
Suppose you are an astronaut in space, hard at
work in your sealed spacesuit. The only way that
you can transfer heat to the environment is by:
A.
B.
C.
D.
Conduction
Convection
Radiation
Evaporation
Physics and Astronomy Outreach Program at the University of British Columbia
Question 3 Answer
Home
Heating
Suppose you are an astronaut in space, hard at
work in your sealed spacesuit. The only way that
you can transfer heat to the environment is by:
A. Conduction
B. Convection
C. Radiation
D. Evaporation
Physics and Astronomy Outreach Program at the University of British Columbia
Question 3 Solution
Home
Heating
In space there is no matter. Both conduction and
convection require matter to transfer heat.
Radiation as means of heat transfer does not
require any medium and there is no exchange of
mass.
Physics and Astronomy Outreach Program at the University of British Columbia
Question 4
Home
Heating
A kWh in B.C. costs currently ~ 7.0 cents. The total energy
consumption in a 1000 ft2 (~100m2) large apartment is
approximately 200 MJ per day. If the apartment is heated
electrically, what’s the energy cost each month?
A.
B.
C.
D.
E.
Less than $ 25
$ 25
$ 50
$ 100
More than $ 100
Physics and Astronomy Outreach Program at the University of British Columbia
Question 4 Answer
Home
Heating
A kWh in B.C. costs currently ~ 7.0 cents. The total energy
consumption in a 1000 ft2 (~100m2) large apartment is
approximately 200 MJ per day. If the apartment is heated
electrically, what’s the energy cost each month?
A.
B.
C.
D.
E.
Less than $ 25
$ 25
$ 50
$ 100
More than $ 100
Physics and Astronomy Outreach Program at the University of British Columbia
Question 4 Solution
Home
Heating
If 3.6 x106 J  1 kWh
Then 200106 J/day  x kWh/day
(200106 J/day) (1 kWh)
x
 55.56 kWh/day
6
3.6 10 J
In one month 55.56 kWh/day 30 days
 1666.67 kWh
So thetotalenergycost in one month:
 1666.67 kWh  $0.07/kWh  $166.67
Physics and Astronomy Outreach Program at the University of British Columbia