# Questions tagged [power]

The time rate of change of energy

590 questions
Filter by
Sorted by
Tagged with
122 views

### What do I measure with power meter?

I modulate directly a laser diode by setting the pump current periodically from 0 A to $I_{on}$ A. I do it for different duty cycles and different frequencies. But I need to keep my average power of ...
76 views

1k views

### Can I use the work done to calculate power of a motor?

I am trying to calculate the energy/ power required to move a plate up and down in a liquid. My approach is to calculate the forces that must be applied by the motor to push/pull the plate based on ...
124 views

### Why does incline on treadmill burn calories faster?

So I was at the gym today, running on the treadmill, when the question hit me: If I run with the treadmill on incline, I burn more calories. Since I run at the same speed, kinetic energy is constant, ...
3k views

### If UV radiation 1 cm away from the halogen bulb is equal to Sun's radiation, what is the level of radiation 1 meter away?

Halogen light bulbs emit some amount of UV radiation, and some sources consider them dangerous. Here it is written, that UV radiation (of certain types) from a particular halogen bulb was equal to the ...
215 views

### Will my car consume more if I plug in my laptop?

I drive a Volvo v40 with a 110hp diesel engine. It usually use 4.6L/100km. If I plug my laptop which is 85W, will this change the fuel need? If so, by how much?
632 views

### Nuclear physics problem, Why do we use high weight atomic elements?

So as far as I know, nuclear fission uses high weight atomic elements to manufacture power. If the risk of runaway reactions are a major reason for not expanding this technology, why don't we use ...
648 views

### Does gravity exert more “power” when an object is traveling faster? [duplicate]

So, this question arose when I was pondering the meaning of horsepower and torque in cars. I thought of the following question: There is a 1 kilogram weight on planet M. Planet M has no atmosphere ...
684 views

### Lorentz engine to run a car?

Could a Lorentz engine (like the ones that move the write head inside of hardrives) be used to run car ? Would it be possable to get it producing 60hp, and a decent amount of tourque, if so how large ...
112 views

### Power in series

I knew that power of two resistors in series is equal to $$\frac{P_1P_2}{P_1+P_2}$$ where $P_1$ and $P_2$ are the individual powers of the two resistors. I tried to prove it using $P=I^{2}R$ and I ...
777 views

### What is the physical meaning of the zeroth component of the Minkowski force 4-vector?

In David Griffiths' Intro to Electrodynamics, section on ED and relativity, he poses a simple problem regarding the zeroth component of the Minkowski force 4-vector for a charge $q$ moving with ...
113 views

### Is power still consumed when we switch off the lights?

I was having heated discussion with one of my friends. We were discussing Earth Hour and its role in saving electricity, and creating awareness. He stated that even if you turn off the lights, the ...
3k views

### Does the mass of a car frame has any effect on its horsepower?

I want to know whether decreasing the mass of the frame of a car will increase its horsepower. From what I understand horsepower is a measure of the car's ability to transport load, and decreasing the ...
3k views

### Confused about unit of kilowatt hours

So I am a little confused on how to deal with the Kilowatt hours unit of power, I have only ever used Kilowatts and I have to design a residential fuel cell used as a backup generator for one day. ...