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Making connections: take-home experiment—electrical energy use inventory

1) Make a list of the power ratings on a range of appliances in your home or room. Explain why something like a toaster has a higher rating than a digital clock. Estimate the energy consumed by these appliances in an average day (by estimating their time of use). Some appliances might only state the operating current. If the household voltage is 120 V, then use P = IV size 12{P = ital "IV"} {} . 2) Check out the total wattage used in the rest rooms of your school's floor or building. (You might need to assume the long fluorescent lights in use are rated at 32 W.) Suppose that the building was closed all weekend and that these lights were left on from 6 p.m. Friday until 8 a.m. Monday. What would this oversight cost? How about for an entire year of weekends?

Test prep for ap courses

The illustration shows a circuit drawn in a rectangle with a long and short parallel on the left and jagged line resistor labeled R on the right side. To the right of the circuit diagram is a graph with and arrow pointing up on the y axis and labeled E. The horizontal axis is represented by an arrow pointing to the right and labeled t. There is a straight diagonal line originating a the origin labeled 0 and ending at t1 on the x-axis (indicated with a dotted line going from t1 to the tip of the line) and E1 on the y-axis (also indicated with a dotted line).

The circuit shown contains a resistor R connected to a voltage supply. The graph shows the total energy E dissipated by the resistance as a function of time. Which of the following shows the corresponding graph for double resistance, i.e., if R is replaced by 2 R ?

  1. There are four graphs with the same x-axis (t) and y-axis (E) shown in figure Ch20S05. All four graphs have straight, diagonal lines ending at t1 (with a dotted line) on the x-axis. The slopes of the line vary; however because they end at different values on the y-axis. Graph A has the steepest slope and the y-ending value for the line is 2E1. Graph B has the second steepest slope and the y-ending value is E1. Graph C's slope is less steep still and ends at E1 over 2. Graph D has the flattest slop and ends at E1 over 4.
  2. There are four graphs with the same x-axis (t) and y-axis (E) shown in figure Ch20S05. All four graphs have straight, diagonal lines ending at t1 (with a dotted line) on the x-axis. The slopes of the line vary; however because they end at different values on the y-axis. Graph A has the steepest slope and the y-ending value for the line is 2E1. Graph B has the second steepest slope and the y-ending value is E1. Graph C's slope is less steep still and ends at E1 over 2. Graph D has the flattest slop and ends at E1 over 4.
  3. There are four graphs with the same x-axis (t) and y-axis (E) shown in figure Ch20S05. All four graphs have straight, diagonal lines ending at t1 (with a dotted line) on the x-axis. The slopes of the line vary; however because they end at different values on the y-axis. Graph A has the steepest slope and the y-ending value for the line is 2E1. Graph B has the second steepest slope and the y-ending value is E1. Graph C's slope is less steep still and ends at E1 over 2. Graph D has the flattest slop and ends at E1 over 4.
  4. There are four graphs with the same x-axis (t) and y-axis (E) shown in figure Ch20S05. All four graphs have straight, diagonal lines ending at t1 (with a dotted line) on the x-axis. The slopes of the line vary; however because they end at different values on the y-axis. Graph A has the steepest slope and the y-ending value for the line is 2E1. Graph B has the second steepest slope and the y-ending value is E1. Graph C's slope is less steep still and ends at E1 over 2. Graph D has the flattest slop and ends at E1 over 4.
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What will be the ratio of the resistance of a 120 W, 220 V lamp to that of a 100 W, 110 V lamp?

10:3 or 3.33

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Section summary

  • Electric power P size 12{P} {} is the rate (in watts) that energy is supplied by a source or dissipated by a device.
  • Three expressions for electrical power are
    P = IV, size 12{P = ital "IV,"} {}
    P = V 2 R , size 12{P = { {V rSup { size 8{2} } } over {R} } ","} {}

    and

    P = I 2 R . size 12{P = I rSup { size 8{2} } R"."} {}
  • The energy used by a device with a power P size 12{P} {} over a time t size 12{t} {} is E = Pt size 12{E = ital "Pt"} {} .

Conceptual questions

Why do incandescent lightbulbs grow dim late in their lives, particularly just before their filaments break?

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The power dissipated in a resistor is given by P = V 2 / R size 12{P = V rSup { size 8{2} } /R} {} , which means power decreases if resistance increases. Yet this power is also given by P = I 2 R size 12{P = I rSup { size 8{2} } R} {} , which means power increases if resistance increases. Explain why there is no contradiction here.

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Problem exercises

What is the power of a 1.00 × 10 2 MV lightning bolt having a current of 2.00 × 10 4 A ?

2 . 00 × 10 12 W size 12{2 "." "00"´"10" rSup { size 8{"12"} } " W"} {}

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What power is supplied to the starter motor of a large truck that draws 250 A of current from a 24.0-V battery hookup?

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A charge of 4.00 C of charge passes through a pocket calculator's solar cells in 4.00 h. What is the power output, given the calculator's voltage output is 3.00 V? (See [link] .)

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Photograph of a small calculator having a strip of solar cells just above the keys.
The strip of solar cells just above the keys of this calculator convert light to electricity to supply its energy needs. (credit: Evan-Amos, Wikimedia Commons)

How many watts does a flashlight that has 6.00 × 10 2 C pass through it in 0.500 h use if its voltage is 3.00 V?

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Find the power dissipated in each of these extension cords: (a) an extension cord having a 0 . 0600 - Ω size 12{0 "." "0600-" %OMEGA } {} resistance and through which 5.00 A is flowing; (b) a cheaper cord utilizing thinner wire and with a resistance of 0 . 300 Ω . size 12{0 "." "300" %OMEGA } {}

(a) 1.50 W

(b) 7.50 W

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Verify that the units of a volt-ampere are watts, as implied by the equation P = IV size 12{P = ital "IV"} {} .

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Show that the units 1 V 2 / Ω = 1 W size 12{1" V" rSup { size 8{2} } / %OMEGA =1" W"} {} , as implied by the equation P = V 2 / R size 12{P = V rSup { size 8{2} } /R} {} .

V 2 Ω = V 2 V/A = AV = C s J C = J s = 1 W

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Show that the units 1 A 2 Ω = 1 W size 12{1" V" rSup { size 8{2} } / %OMEGA =1" W"} {} , as implied by the equation P = I 2 R size 12{P = I rSup { size 8{2} } R} {} .

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Verify the energy unit equivalence that 1 kW h = 3 . 60 × 10 6 J size 12{1" kW" cdot "h = 3" "." "60"´"10" rSup { size 8{6} } " J"} {} .

1 kW h= 1 × 10 3 J 1 s 1 h 3600 s 1 h = 3 . 60 × 10 6 J size 12{1" kW" cdot "h=" left ( { {1 times "10" rSup { size 8{3} } " J"} over {"1 s"} } right ) left (1" h" right ) left ( { {"3600"" s"} over {"1 h"} } right )=3 "." "60" times "10" rSup { size 8{6} } " J"} {}

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Questions & Answers

Three charges q_{1}=+3\mu C, q_{2}=+6\mu C and q_{3}=+8\mu C are located at (2,0)m (0,0)m and (0,3) coordinates respectively. Find the magnitude and direction acted upon q_{2} by the two other charges.Draw the correct graphical illustration of the problem above showing the direction of all forces.
Kate Reply
To solve this problem, we need to first find the net force acting on charge q_{2}. The magnitude of the force exerted by q_{1} on q_{2} is given by F=\frac{kq_{1}q_{2}}{r^{2}} where k is the Coulomb constant, q_{1} and q_{2} are the charges of the particles, and r is the distance between them.
Muhammed
What is the direction and net electric force on q_{1}= 5µC located at (0,4)r due to charges q_{2}=7mu located at (0,0)m and q_{3}=3\mu C located at (4,0)m?
Kate Reply
what is the change in momentum of a body?
Eunice Reply
what is a capacitor?
Raymond Reply
Capacitor is a separation of opposite charges using an insulator of very small dimension between them. Capacitor is used for allowing an AC (alternating current) to pass while a DC (direct current) is blocked.
Gautam
A motor travelling at 72km/m on sighting a stop sign applying the breaks such that under constant deaccelerate in the meters of 50 metres what is the magnitude of the accelerate
Maria Reply
please solve
Sharon
8m/s²
Aishat
What is Thermodynamics
Muordit
velocity can be 72 km/h in question. 72 km/h=20 m/s, v^2=2.a.x , 20^2=2.a.50, a=4 m/s^2.
Mehmet
A boat travels due east at a speed of 40meter per seconds across a river flowing due south at 30meter per seconds. what is the resultant speed of the boat
Saheed Reply
50 m/s due south east
Someone
which has a higher temperature, 1cup of boiling water or 1teapot of boiling water which can transfer more heat 1cup of boiling water or 1 teapot of boiling water explain your . answer
Ramon Reply
I believe temperature being an intensive property does not change for any amount of boiling water whereas heat being an extensive property changes with amount/size of the system.
Someone
Scratch that
Someone
temperature for any amount of water to boil at ntp is 100⁰C (it is a state function and and intensive property) and it depends both will give same amount of heat because the surface available for heat transfer is greater in case of the kettle as well as the heat stored in it but if you talk.....
Someone
about the amount of heat stored in the system then in that case since the mass of water in the kettle is greater so more energy is required to raise the temperature b/c more molecules of water are present in the kettle
Someone
definitely of physics
Haryormhidey Reply
how many start and codon
Esrael Reply
what is field
Felix Reply
physics, biology and chemistry this is my Field
ALIYU
field is a region of space under the influence of some physical properties
Collete
what is ogarnic chemistry
WISDOM Reply
determine the slope giving that 3y+ 2x-14=0
WISDOM
Another formula for Acceleration
Belty Reply
a=v/t. a=f/m a
IHUMA
innocent
Adah
pratica A on solution of hydro chloric acid,B is a solution containing 0.5000 mole ofsodium chlorid per dm³,put A in the burret and titrate 20.00 or 25.00cm³ portion of B using melting orange as the indicator. record the deside of your burret tabulate the burret reading and calculate the average volume of acid used?
Nassze Reply
how do lnternal energy measures
Esrael
Two bodies attract each other electrically. Do they both have to be charged? Answer the same question if the bodies repel one another.
JALLAH Reply
No. According to Isac Newtons law. this two bodies maybe you and the wall beside you. Attracting depends on the mass och each body and distance between them.
Dlovan
Are you really asking if two bodies have to be charged to be influenced by Coulombs Law?
Robert
like charges repel while unlike charges atttact
Raymond
What is specific heat capacity
Destiny Reply
Specific heat capacity is a measure of the amount of energy required to raise the temperature of a substance by one degree Celsius (or Kelvin). It is measured in Joules per kilogram per degree Celsius (J/kg°C).
AI-Robot
specific heat capacity is the amount of energy needed to raise the temperature of a substance by one degree Celsius or kelvin
ROKEEB
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Source:  OpenStax, College physics for ap® courses. OpenStax CNX. Nov 04, 2016 Download for free at https://legacy.cnx.org/content/col11844/1.14
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