ses 141 exam 3
if your brain consumes 10x the amount of energy as any other part of your body by mass, estimate the power the brain uses (watt)
1.11 watt x 10 = 11.1 watt
what is the energy density of fusion fuels
100 terrajoules
a collection of molecules holding a charge of 16 coulombs all pass through a hole in 4 seconds. what is the current (in amps) through the hole?
16/4=4
suppose the electric field between two points separated by 17 meters is 22 volt/m. what is the electric potential (in volt) between the two points? Use exact numbers; do not estimate
17x22=374
estimate the average time a typical person spends brushing their teeth (in minutes)
2 minutes
estimate recommended daily intake for the average american adult
2000 calories
a household washing machine connected to a household 222 volt source draws 2 amp of current. what is the power (in watt) being supplied to the washing machine? use exact numbers; do not estimate
222(2)=444
every charge has an ________ field
electric
differences between fission and fusion include
fission breaks apart heavier nuclei into lighter nuclei fusion combines light nuclei into heavier nuclei
estimate the energy (in joule) of a tornado
30,000,000,000
estimate the average mass of an adult human brain (kg)
brain mass = approx 3 lbs = 1.4 kg
A coil of wire with a current is often called an _________
electromagnet
energy flows in an electrical circuit
parallel to and outside the wires
some properties of a magnetic field include
the magnetic field of a wire is concentric circles every current has a magnetic field every moving charge has a magnetic field
estimate average daily power your body consumes (watt)
(2000x4.2)/(24x2600) = 0.146kwatt = 146 watt
assuming 100% efficiency of extracting geothermal energy, estimate the ratio of geothermal energy to human's current annual world consumption of energy
(4.32e18 joules) / (1.6e18) = 2.70
the flow of energy from earth's interior to the surface is about 50 terawatt (1 terawatt = 1e12 joule/sec). estimate how much geothermal energy reaches Earth's surface in one day (in joule)
1 terawatt = 1e12 joule/sec) 50 terawatt = 50e12 joule/sec 1 day = 86400 seconds 86400 x 50e12 = 4.32e18 joule
estimate the number of people in the world
7e9
estimate the percentage of people who brush their teeth
85%
some properties of a voltage and a current are
a charge is a current a voltage is energy divided by a charge a current is a charge divided by a time
some of the main sources of radioactivity we encounter in everyday life are
air the cosmos food the earth
estimate the power your brain uses if it uses the same amount of energy as any part of your body (watt)
brain = approx 230 kcalories a day = 23 calories power = (23x4.2)/(24x3600) - 0.00111 kwatt = 1.11 watt
some properties of an electric field include
electric field lines from positive and negative charges interact with each other electric field lines from positive charges point outward every charge has an electric field
some properties of the particles that are sources of electric charge include
electrons carry a negative charge, protons carry a positive charge electrons usually move freely within a solid material electric charge comes in bundles of any size
laser fusion attempts fusion reactions by _________ and compressing a fuel target
heating
two key problems for controlled fusion on Earth are _______ and containment
heating
fission decomposes ____ nuclei into ____ nuclei.
heavy, lighter
the types of emission that mostly occur when an isotope undergoes radioactive decay include
helium nuclei gamma-ray photons electrons
estimate humanity's current consumption of energy in one day (in joule).
human consumption = approx 18 terawatt = 18e12 joule/sec 86400 x 18e12 = 1.60e18 joule
estimate average mass of a human (kg)
human mass = approx 200 lbs = 90 kg
laser fusion
implodes a fuel pellet uses nuclear reactions to produce energy
fusion combines ____ nuclei into ____ nuclei.
light, heavier
a magnetic field is caused by a _______ electric charge
moving
similarities and differences between chemical and nuclear energy sources include
nuclear reactions release a million times more energy than chemical reactions
electric field lines from positive charges point radially ______ , and point radially _______ for negative charges
outward, inward
alternating current (ac) is the _________ flow of electric charge.
periodic
peas have a diameter of about 0.1 cm. Estimate the number of peas that fit in a gallon jar
radius of pea: 0.05 cm 1 gallon = 3875.4 cm n(4/3)(pi)(0.05)^3 = 3785.4 n = 3785.4(3/4)(1/pi)(1/0.05^3) n = 7,229,581
the fraction of people doing any activity is equal to the fraction of time it takes to do that activity. in symbols, n/n_total = t/t_total. estimate the number of people brushing their teeth right now
t = 2 minutes t_total = 24 x 60 minutes n = ? n_total = 7e9 n = (2x7e9) / (24x60) = approx. 9,800,00
some properties of energy flow in a circuit include
the electric and magnetic lines are always at 90 degrees to each other electrons flow in the wires energy flows outside and parallel to the wires energy flows from both terminals of a DC battery to the load and never returns to the battery
if the distance between two electrons is doubles, what would happen to the electric force between them
the electric force would be 1/4 as strong
in electronic circuits
the power used by a circuit is the current times the voltage the power used by a circuit is the resistance times the current squared electric and magnetic fields are transporting the energy
a clothes washer used 4 kilowatt for 0.7 hour. if electricity costs $0.32 per kilowatt-hour, how much did it cost (in dollars, to the nearest penny) to use the clothes dryer?
total energy = 4 x 0.7 = 2.8kwh total cost - 2.8 x 0.32 = $0.90
direct current (dc) is the ____________ flow of electric charge.
unidirectional
