I am trying to independently solve physics problems and I am attempting to solve Chapter 5 problem 4-4 on page 140 from the book "Feynman's Tips on Physics".
The problem is as follows:
A painter weighing 180 lbs working from a "bosun's" chair hung down the side of a tall building desires to ...
Can the vector potential for a static homogeneous magnetic field contain parallel components?
A simple example for a vector potential for that is $\mathbf{A}=\vec{r}x\mathbf{B}$ which obviously doesn't. But then due to gauge-invariance any $\vec{r}x\mathbf{B}+\grad f(\vec{r})$ will be as good. Now I fail to have a proper intuition for what $\grad f(\vec{r})$ could all possibly look like.
Considering the ideal gas law , where pressure is always positive, i wonder :
How can gravity turn a gas into a star ?
Yes gas has mass too.
But a light gas obeing the ideal gas law seems problematic to me ?
Without the pressence of other matter or gravity not from the gas , I think a star ca...
Which properties of the nucleons cannot be derived from that of the theory of quarks and gluons? Why? Are these properties no derivable in principle or is it due to limited computational power?
Take the Schwarzschild equivalent in $1+1$ dimensions, that would be
$$ds^2 = -f(r) dt^2 + \frac{1}{f(r)} dr^2$$
We'll also require that $f(r)$ be asymptotically flat (just for being a "realistic" potential) and that it is non-singular (so that the particle can't crash in the singularity). The ...
I don't understand when we say "A certain appliance uses 350W of energy..." what do we mean by that? This much energy per hour? Or when we say a battery has a capacity of 20Ah we mean that if the load draws 20Amps of current, it will do it for 1 hour?
"A certain appliance uses 350 W. If it is allowed to run continuously for 24 days, how many kilowatt-hours of energy does it consume?" I have this exercise. What are they asking? How many kilowatts per hour it consumes?
They give you the power of the device (i.e. the rate at which it consumes energy) and a length of time. They want you to compute the total energy consumed.
Well... a Joule is a unit of energy and Watt is just...
:: googles ::
It's a unit of power.
The watt (symbol: W) is a unit of power. In the International System of Units (SI) it is defined as a derived unit of 1 joule per second,[1] and is used to quantify the rate of energy transfer.
Think by analogy with velocity. If something has a velocity of 0.35km/s, you wouldn't say 0.35km/s is the distance it travels per second. 0.35km is the distance per second.
So 576 hours. So the device has power of 0.35kW (Consumes 0.35kJ of energy per second). From here we multiply 0.35kW * 576 and we get the answer that says how many kilojoules of energy have been consumed for these 576 hours?
"If you used 400 W of power for 30 h, you have used:" I still don't understand how you can 'use' power. I though energy can be used and pwoer is just the rate at which they are used?
it's no different than saying that mpg-liters are a unit of distance: namely, the distance traveled by a car rated at 1 mile per gallon of gas if supplied by 1 liter of gas.
"A given power supply is capable of providing 6 A for 3.5 h. Its ampere-hour rating is". Ah = A * h. So we have 6A * 3.5h? I guess that's the way but what exactly does Ah tells us?
Yep, I think I quite understand the concepts of kWh and Ah. Can you give me and exercise please because I don't find any. If you don't have time, no problems, I know i'm asking for a lot.
you do see it occasionally, though, as a consequence of Faraday's law
anyways, the statement that 1 watt-hour = 1 amp-hour*volt then amounts to the claim: 1 watt-hour is the amount of energy required to transfer 1 amp-hour of charge across 1 volt of potential difference.
i.e. W= QV
which is just what it should be, since potential difference is defined as work per unit charge.
So if I see at a battery that it says "Typ. 5Ah" it means (5C/s) * (3600 s). From there we get 18000C so that's the total amount of coloumbs that the battery can give out? And if a load draws 2.5A (2.5C/s) it means, the battery can supply that load for 2 hours?
Ok, slowly but surely I'm getting used to these Ah and kWh. Thanks @Semiclassical so much for helping me out. I've actually learned more here for 6 months that I have in school for 9 years.
Well, that'd require you to multiply by 1 volt first
and you'd have to have a reason to do so
for instance, you might put the battery into a circuit and determine that 2 amps are being drawn off the battery and that the voltage difference across the battery is 1 volt
in that case, a 5Ah battery will last 2.5 hours and will supply 5Wh of energy to the circuit in that time
Ok if I have a battery that can supply a total of 4Ah (14400 Coulobs of charge) and the voltage across the battery is 2 volts, then Wh = Ah * V, so Wh = 4 * 2, we get 8Wh of energy this circuit will consume in the total lifespan of the battery?
If you had a different setting with a different operating voltage / current, then naturally the circuit would last a different amount of time and provide a different amount of energy.
And? If there's no other power sources, then the 3Wh of energy consumed by the circuit had better be supplied by the battery. otherwise you'd be violating energy conservation.
that aside, though, any energy supplied by the battery must either be consumed by a resistor or stored in some part of the circuit e.g. energy stored in a capacitor
On a plank inclined at an angle $\alpha$ , a body of mass $m$ is kept and accelerated upwards along the plank at an acceleration $a$ with a thread inclined with the plank at an angle $\beta$ . The coefficient of kinetic friction of the plank is $k$ . I need to find the value of $\beta$ for whi...
@Semiclassical In all the parts of the US where I have lived kWh is the unit on the electrical meter on the side of your house, and most home owners have at least a vague idea of how many they go through in a billing cycle.
How are the meters in other parts of the world marked?
No idea. I'm not a homeowner myself, so I haven't had much direct experience with them. (And I am in the US, so I wouldn't have insight outside the US regardless)
if i'm writing something in LaTeX and I have a line that goes out of bounds (it's a line of code i'm putting in using lstlisting) but adding a return would, if the code was copy-pasted, produce a multitude of errors, what should I do to make the output readable and usable?
@dmckee well...there's yet another difficulty...I don't know what's exactly allowed or not by the journal - i'm trying to follow their style guide but it's meant for editors not authors, but the author page refers to this style guide =/
I need a project for that, though. I think I know what I'd do but the last time I tried to do it in Mathematica (which I know pretty well) I just got tired of it
@Mithrandir24601 All names in ABAP have underscores because the language is not case sensitive and the stupid auto-formatter will gut any case-sensitive formatting eventually :'(
I am trying to independently solve physics problems and I am attempting to solve Chapter 5 problem 4-4 on page 140 from the book "Feynman's Tips on Physics".
The problem is as follows:
A painter weighing 180 lbs working from a "bosun's" chair hung down the side of a tall building desires to ...
Considering the ideal gas law , where pressure is always positive, i wonder :
How can gravity turn a gas into a star ?
Yes gas has mass too.
But a light gas obeing the ideal gas law seems problematic to me ?
Without the pressence of other matter or gravity not from the gas , I think a star ca...
Which properties of the nucleons cannot be derived from that of the theory of quarks and gluons? Why? Are these properties no derivable in principle or is it due to limited computational power?
Take the Schwarzschild equivalent in $1+1$ dimensions, that would be
$$ds^2 = -f(r) dt^2 + \frac{1}{f(r)} dr^2$$
We'll also require that $f(r)$ be asymptotically flat (just for being a "realistic" potential) and that it is non-singular (so that the particle can't crash in the singularity). The ...
