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
$P=\text{IV}$ . 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?
Section summary
Electric power
$P$ is the rate (in watts) that energy is supplied by a source or dissipated by a device.
Three expressions for electrical power are
$P=\text{IV,}$
$P=\frac{{V}^{2}}{R}\text{,}$
and
$P={I}^{2}R\text{.}$
The energy used by a device with a power
$P$ over a time
$t$ is
$E=\text{Pt}$ .
Conceptual questions
Why do incandescent lightbulbs grow dim late in their lives, particularly just before their filaments break?
The power dissipated in a resistor is given by
$P={V}^{2}/R$ , which means power decreases if resistance increases. Yet this power is also given by
$P={I}^{2}R$ , which means power increases if resistance increases. Explain why there is no contradiction here.
What is the power of a
$1.00\times {\text{10}}^{\text{2}}\phantom{\rule{0.25em}{0ex}}\text{MV}$ lightning bolt having a current of
${\mathrm{2.00\; \times \; 10}}^{\text{4}}\phantom{\rule{0.25em}{0ex}}\text{A}$ ?
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] .)
How many watts does a flashlight that has
$6.00\times {\text{10}}^{\text{2}}\phantom{\rule{0.25em}{0ex}}\text{C}$ pass through it in 0.500 h use if its voltage is 3.00 V?
Find the power dissipated in each of these extension cords: (a) an extension cord having a
$0\text{.}\text{0600}\phantom{\rule{0.25em}{0ex}}\text{-}\phantom{\rule{0.25em}{0ex}}\Omega $ resistance and through which 5.00 A is flowing; (b) a cheaper cord utilizing thinner wire and with a resistance of
$0\text{.}\text{300}\phantom{\rule{0.25em}{0ex}}\Omega .$
Show that the units
$1\phantom{\rule{0.25em}{0ex}}{\text{A}}^{2}\cdot \Omega =1\phantom{\rule{0.25em}{0ex}}\text{W}$ , as implied by the equation
$P={I}^{2}R$ .
Verify the energy unit equivalence that
$1\phantom{\rule{0.25em}{0ex}}\text{kW}\cdot \text{h = 3}\text{.}\text{60}\times {\text{10}}^{6}\phantom{\rule{0.25em}{0ex}}\text{J}$ .
Electrons in an X-ray tube are accelerated through
$1.00\times {\text{10}}^{\text{2}}\phantom{\rule{0.25em}{0ex}}\text{kV}$ and directed toward a target to produce X-rays. Calculate the power of the electron beam in this tube if it has a current of 15.0 mA.
An electric water heater consumes 5.00 kW for 2.00 h per day. What is the cost of running it for one year if electricity costs
$\text{12.0 cents}\text{/kW}\cdot \text{h}$ ? See
[link] .
Scalar quantity
Because acceleration has only magnitude
Bob
acleration is vectr quatity it is found in a spefied direction and it is product of displcemnt
bhat
its a scalar quantity
Paul
velocity is speed and direction. since velocity is a part of acceleration that makes acceleration a vector quantity. an example of this is centripetal acceleration. when you're moving in a circular patter at a constant speed, you are still accelerating because your direction is constantly changing.
Josh
acceleration is a vector quantity. As explained by Josh Thompson, even in circular motion, bodies undergoing circular motion only accelerate because on the constantly changing direction of their constant speed. also retardation and acceleration are differentiated by virtue of their direction in
fitzgerald
respect to prevailing force
fitzgerald
What is the difference between impulse and momentum?
Manyo
Momentum is the product of the mass of a body and the change in velocity of its motion.
ie P=m(v-u)/t (SI unit is kgm/s). it is literally the impact of collision from a moving body.
While
Impulse is the product of momentum and time.
I = Pt (SI unit is kgm) or it is literally the change in momentum
what impulse is given to an a-particle of mass 6.7*10^-27 kg if it is ejected from a stationary nucleus at a speed of 3.2*10^-6ms²? what average force is needed if it is ejected in approximately 10^-8 s?
John
speed=velocity÷time
velocity=speed×time=3.2×10^-6×10^-8=32×10^-14m/s
impulse [I]=∆momentum[P]=mass×velocity=6.7×10^-27×32×10^-14=214.4×10^-41kg/ms
force=impulse÷time=214.4×10^-41÷10^-8=214.4×10^-33N.
dats how I solved it.if wrong pls correct me.
temperature is the measurement of hotness or coldness of a body...
heat transfer is the movement of heat from one body to another
Doc
U get it right
Titilayo
correct
PROMISE
heat is an energy possesed by any substance due to random kinetic energy possesed by molecules while temperature is driving force which gives direction of flow heat