Hot answers tagged

12 votes

Why is Power = Voltage $\times$ Current?

multiplying the rate of flow which is the amount of coulombs passing through a cross sectional area by the potential difference seems very difficult to connect Sorry, but there isn't much more to it ...
user avatar
  • 22.7k
5 votes

Why is Power = Voltage $\times$ Current?

Consider a charge $q$ moving with speed $v$. In $t$ seconds it will move a distance $d=vt$, so the current (charge per second passing by that cross section area) is $I = q/t = qv/d$. Electric field ...
user avatar
  • 21.3k
4 votes

Why is Power = Voltage $\times$ Current?

Force on a charge $\lambda dl$ $f dl = \lambda \vec{E} dl$ Amount of work done by $\vec{E}$ moving a charge $\lambda dl$ with a velocity $\vec{v}$ in time dt $dw = \lambda \vec{E} \cdot \vec{v} dl ...
user avatar
  • 3,662
4 votes

Why is Power = Voltage $\times$ Current?

To get a basic intuition for electrical equations I tend to think of a hydrological analogue. When water is moving through waterways, the difference in elevation corresponds to a potential difference, ...
user avatar
3 votes

Is energy infinite in an electric field?

"Can move it an infinite distance" is no way to measure energy. Give an object any amount of kinetic energy, and in the presence of no other forces, It will move an infinite distance. $\int_{...
user avatar
  • 3,662
3 votes

Why is Power = Voltage $\times$ Current?

Along the lines of the answer by @garyp , it might be good to note that $VI=Fv$ in that answer hints of a "mechanical analogy". Thinking in terms of [generalized-]work (as mechanics or ...
user avatar
  • 7,943
2 votes

Why is Power = Voltage $\times$ Current?

Other answers address why power is given by the product of voltage and current, on grounds of physics. Regardless of the physical meaning we associate with this product, the sum of voltage-current ...
user avatar
  • 7,257
2 votes

What exactly is the limiting factor of the efficiency of a heat engine?

What exactly is the limiting factor of the efficiency of a heat engine? The short answer to the title of your post, the limiting factors are the maximum and minimum temperatures between which the ...
user avatar
  • 55.4k
2 votes
Accepted

Conservation of energy and work done by a torque

The solid is assumed to be a rigid body. Friction causes rotation and does do rotational work with respect to the center of mass. But, for no slipping of a rigid body, the net work from friction is ...
user avatar
  • 5,825
2 votes

Is work done by torque due to friction in pure rolling?

Which answer is correct? The second answer is correct*. For some reason, friction tends to mentally twist people in knots. It is just an ordinary mechanical force and obeys all of the usual rules ...
user avatar
  • 64.2k
2 votes

In an isothermal process there is no change in internal energy, but why in an isobaric one?

But why doesn't this also happen in the isobaric process? Volume work is also done there. Because unlike the isothermal process where the initial and final temperatures are the same making $\Delta U=...
user avatar
  • 55.4k
1 vote
Accepted

Work done by battery

In an inductive circuit, the current never stops flowing. It tends towards a maximum value (assuming some amount of resistance, for the circuit to heat up.) If E is the emf of the battery, L is the ...
user avatar
  • 56
1 vote

What is the source of isothermal work?

In the isothermal reversible expansion of a non-ideal gas, $dU=C_vdT+\xi dV$, where $\xi$ is a function of the non-ideal PVT behavior of the gas. For isothermal expansion, you would then have $$dU=\...
user avatar
  • 27.7k
1 vote

What is the source of isothermal work?

What happens to the "unused" absorbed "heat" inside the working substance; e.g., will it get converted later into something else, etc.? The problem may lie in part with this ...
user avatar
1 vote

Is work done by torque due to friction in pure rolling?

Setting the second Newton's law of the situation, and using the definition of work: The net force for rolling without slip in an incline is $mgsin(\theta) - f_f$, where $\theta$ is the angle of the ...
user avatar
1 vote

Is work done by torque due to friction in pure rolling?

Work is clearly done. The body speeds up and spins faster. First torque is the result of two parallel forces displaced sideways from each other. See Toppling of a cylinder on a block for more. One ...
user avatar
  • 25.5k
1 vote

Is work done by torque due to friction in pure rolling?

Work depends on frame of reference. The reason is that, displacement also depends on frame of reference. We have three ways of analyzing work done by friction. If reference is ground, work done by ...
user avatar
1 vote

What exactly is the limiting factor of the efficiency of a heat engine?

Let us consider gas, cylinder, and a piston. The only energy that the gas has is thermal energy. The only work the gas does is pushing the piston From 1 and 2 it follows that: lost thermal energy =...
user avatar
  • 1,495
1 vote

Are there two work-energy theorems (rotational and translational) or just a single theorem for both?

The total kinetic energy of a system of particles is the sum of (a) the translational kinetic energy of the center of mass (CM) plus (b) the kinetic energy of motion about the CM. Term (a) is ${1 \...
user avatar
  • 5,825
1 vote
Accepted

Are there two work-energy theorems (rotational and translational) or just a single theorem for both?

Perhaps a derivation. For an extended body, let $\vec R$ describe the motion of the center of mass, and let $\vec r'$ be the position of a point on the rigid body with respect to the center of mass, ...
user avatar
  • 6,298
1 vote

Are there two work-energy theorems (rotational and translational) or just a single theorem for both?

What you call the "traditional work-energy theorem" is its application to a particle, or to an extended object where the direction of the net force acting on the object is through its center ...
user avatar
  • 55.4k
1 vote

Are there two work-energy theorems (rotational and translational) or just a single theorem for both?

To make a clarification, I am unsure about relativistic effects, so I assume we are only considering non-relativistic speeds. To answer your question, it is important to define our translational and ...
user avatar
1 vote

Is there a formula of heat that expresses it in microscopic work done?

Your last equation is an expression for the change in internal energy, specifically, the change in the molecular kinteic energy component of internal energy, not heat. There is no such thing as a &...
user avatar
  • 55.4k
1 vote
Accepted

How to justify that Carnot loop for ideal gas is closed on two sides by adiabatic curves?

The segments are adiabatic (no heat transfer) because the system needs to be brought from temperature of one reservoir to temperature of the other. This can't happen while in contact with any of the ...
user avatar
1 vote
Accepted

Understanding the shape of Carnot loop in the $p$-$V$ plane

It seems that an isobaric path gives the most work per volume. My first observation regarding your drawing of the cycle is that while you are showing heat being added during the isobaric expansion ...
user avatar
  • 55.4k
1 vote

Understanding the shape of Carnot loop in the $p$-$V$ plane

In carnot engine we care about maximising the efficiency, i.e how much useful work we get out the given heat. Now what is interesting to note is that any reversible engine working between two ...
user avatar
1 vote

Why is Power = Voltage $\times$ Current?

"Power" as a concept, on its own, doesn't really make a lot of sense unless you think about what is doing the work. That's because that's what it is: it is the rate of doing work or more ...
user avatar
1 vote

Why is Power = Voltage $\times$ Current?

Let's take water as an analogy. V is the height of fall of the water and I is the volume that falls on the mill wheel. In electricity, V is the potential difference between the source and the sink and ...
user avatar
1 vote

Why is Power = Voltage $\times$ Current?

Simplify it. Power is energy in application of delivery to a new or transitioning it's system. The qualities of a engine, motor or conductor dictate how much energy shall be delivered as power in ...
user avatar
1 vote

Why is Power = Voltage $\times$ Current?

The force over the charge of a small volume in an electric field is: $\delta F = \delta q E = \rho A\delta x E$, where $\rho$ is the local density of movable charges and $A$ the wire cross section. If ...
user avatar

Only top scored, non community-wiki answers of a minimum length are eligible