All Questions
39 questions
0
votes
1
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115
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Understand power rating in layman terms
I have recently started the chapter of electricity of class 8. I am not understanding the concept of power rating of appliances. When we say that a bulb is rated 220V-100W, which means, according to ...
- 213k
13
votes
5
answers
4k
views
Watts vs. volts amperes
What I understand:
In simple DC circuits, this is a product of the current and voltage, such that 1 watt = 1 ampere x 1 volt
I understand that a watt is a unit of power (change in energy per unit ...
11
votes
3
answers
5k
views
Why high voltage transmission lines?
This is a question which I seem to have tackled multiple times, solved each time after reading a dodgy internet explanation, then partially forgotten about and retackled half a year later. It is time ...
- 6,269
21
votes
8
answers
14k
views
Why do we reduce only current to prevent power loss? Why not voltage?
In power transmission lines current is kept low and voltage is kept high to reduce the power loss. This is because $P = I^{2}R$ and $P = VI$. In order to reduce power loss we have to reduce $I$ since $...
- 2,085
0
votes
1
answer
460
views
Why is the brightness of a light bulb dependant on power?
If:
Temperature is a measure of the average (kinetic) energy of the particles which make up some material
Power is measure of energy transferred per second (J/s)
The temperature of the filament in a ...
- 33
0
votes
1
answer
80
views
"Why do power lines use high voltage?" Loss in power equal to Current*Voltage? [duplicate]
I define P is the average power. So $P=IV$ and $I=\frac{P}{V}$.
$P_{loss}$ I define to be the power loss, which is equal to $I^2R$.
Substituting for $I$, $P_{loss} = \frac {P^2R}{V^2}$
So I get that ...
- 56.5k
1
vote
1
answer
124
views
Transformers in Power transmission [duplicate]
Recently I learnt that transformers are used in the national grid to increase the voltage, so we get less current. But my understanding V=IR and by increasing the voltage we get more current, so what ...
- 36.6k
-1
votes
1
answer
220
views
How same power is distributed in different voltages in power lines?
I have seen when a resistor is connected to a battery, it carries the same voltage across the resistor, if the resistance is changed the current changes but voltage remains the same making the battery ...
CommunityBot
- 1
1
vote
1
answer
229
views
High voltage in transmission line [closed]
I'm trying to understand why high voltage is used in transmission but I seem really confused by the explanations I read.
Here's what I could make out:
$$P_\text{loss} = \dfrac{ΔV^2}{R_t} = \dfrac{(...
- 349
2
votes
2
answers
671
views
Ohm's law and Joules heating
Ohm's law state that the ratio of V and I gives us a constant value of R provided that the temperature is kept constant throughout. However, in accordance with the joule's heating it would get heated ...
- 58.6k
0
votes
1
answer
273
views
Power and power loss during transmission of power
So let's say power to be delivered to homes is 80 kW($P_3$ = 80 kW) and the houses have to receive it at 220 V ($V_3$ = 220 V). The substation is a 4000 V to 220 V step-down transformer and $R_2=15\ \...
- 213k
2
votes
1
answer
606
views
Power loss in power cable contradiction
To minimize the power loss in long-distance power cables it is best to minimize the current and maximize the voltage. This is because the power loss in the cable is calculated by $P=VI$, which we can ...
- 213k
11
votes
1
answer
2k
views
High voltage power lines - clarification of energy loss
I've been having a bit of trouble understanding the high-voltage power lines. If I was sending power from $A \rightarrow B$, we have:
Ohm's law $V = IR$
Power lost in the form of heat $P = I^2 R$
...
- 2,350
1
vote
2
answers
40
views
Resistance And Electric Power
In a practice problem A motor rated at 20 A with a voltage of 115V exerts a force of 4900 N over a distance of 10 m in 30 s. Using the formulas $P=VI$ and $P=\frac{Fs}{t}$, we can see that the motor ...
- 4,936
84
votes
6
answers
24k
views
Why does public mains power use 50-60 Hz and 100-240 V?
Is there a physical reason behind the frequency and voltage in the mains electricity? I do not want to know why exactly a certain value was chosen; I am rather interested to know why that range/order ...
- 25.3k
2
votes
3
answers
181
views
What does an $x$ Watt bulb actually means?
Let's say I have a 11W bulb in my home, connected to a 220V power supply. What exactly does it mean that this bulb is 11W? As far as I know, the Wattage is determined by the formula $W = V * I$, so it ...
- 22.1k
0
votes
2
answers
324
views
Why current drops when voltage increases?
https://www.youtube.com/watch?v=ubZuSZYVBng&t=329s
In the video above the man put a 200 thousands volt ball near a non-charged one and a very tiny current appear between them. But I think with ...
- 77.9k
0
votes
2
answers
152
views
Electrical energy (J) from voltage (V), amperage (A) and exposure duration (s)
I have that the electrical energy $E$ in Joules (J) is equal to $E = time \times current^2 \times resistance$.
Reasoning with SI units, we can verify that this equation does return energy values in ...
- 77.9k
1
vote
2
answers
368
views
When to use Ohm's law as opposed to using power formula?
I am a mechanic trying to gain a better understanding of electrical theory on vehicles. I have a sound understanding of Ohm's law and also the power formula (Power = Voltage x Current)
However, I am ...
- 97.8k
8
votes
4
answers
2k
views
What's the point of an RMS value? [duplicate]
the RMS (root mean square) value of $f(x)$ is defined as:
$$f(x)_{rms}=\sqrt{\frac{\int^b_a (f(x))^2dx}{b-a}}$$
Why do we do this very specific thing of taking the square, the mean, and then the ...
1
vote
3
answers
685
views
What is meant by transmission voltage?
I had a question in class that went :
$120$kW of power is generated at a power plant and is then transmitted. The resistance in the transmission lines is $0.4 \Omega$. Calculate the power lost as ...
- 13k
5
votes
6
answers
16k
views
How power lines use high voltages with a low current?
I've read that power lines use high voltages and low currents to reduce power loss due to resistance. Looking at the formula for power -
P = VI
So to increase P, you increase V rather than I for ...
- 213k
0
votes
2
answers
86
views
Electrical vs Heating Insulation
Let's say we have a 120V cable and a 600V cable, this means that the 600V needs more electrical insulation to prevent the insulator from exceeding its dielectric strength. But in the other case, the ...
- 26.6k
0
votes
2
answers
3k
views
Why High Voltage Power Lines need more Insulation than a low one?
"A 400 kV cable requires less insulation than a 240V cable."
This was regarded as False in one of my question papers, but why? Doesn't a higher voltage means, lower current(P=V. I) and a lower ...
- 77.9k
0
votes
2
answers
318
views
Is 220 V, 50 A equally dangerous for a person as 1A, 11000 V? [duplicate]
The question is self-explanatory. I'm a high school student so feel free to use scientific terms.
- 1,130
4
votes
4
answers
14k
views
What does it mean when we say that power of a bulb is 10 W? Since $V/I=$ resistance is a constant, how can power $=VI$ be a constant?
My question is simple. In Ideal situation, at constant temperature, we know that normal appliances like a filament bulb has straight Voltage vs Current graph, meaning its resistance is constant or ...
1
vote
2
answers
550
views
Electric power and resistance dependance
According to the equations,
$$P=VI =I^2R\,\text{ and voltage } V=IR$$
it seems clear that when the resistance is lower by fixing the voltage at constant, the current is therefore, higher, generating ...
- 10.2k
2
votes
2
answers
39k
views
Confusion about P=VI and V=IR
If we look at $P=VI$, we see that if the current doubles then the potential difference is halved
but this doesn't seem to make sense according to $V=IR$. If we look at that equation, since the ...
CommunityBot
- 1
0
votes
0
answers
49
views
Transformer vs Inductor for lighting a bulb or any other appliance
There was a question in my school physics exam which is as follows:
Consider a 100W bulb which operates at 50V dc. John wants to light this bulb by a 200V ac source. What component should he use, ...
- 288
0
votes
4
answers
3k
views
How can AC source with different voltage provide same power?
As some of us maybe aware, USA mains connection is 110 V while those in Asian countries are 220 V. How is it still possible for the Adapter to provide the necessary power to the device, say a laptop, ...
- 16.2k
2
votes
1
answer
84
views
Won't the Power be dissipated in the first quadrant of this graph?
In the following picture:
In the first quadrant of the V-I graph(for an Independent Current Source, where the voltage supplied is positive on the top) won't the power be dissipated instead of being ...
- 60.3k
0
votes
2
answers
2k
views
What's the relation between output voltage and time to boil water given the same kettle?
An electric kettle rated 220V, 2000W needed 10 minutes to boil water when it is half filled with water in Singapore where the output voltage is 220V. Estimate the amount of time needed to do the same ...
CommunityBot
- 1
3
votes
2
answers
4k
views
Electric power for current density
The electric power produced by a current $I\in\mathbb{R}^+$ and a voltage $V\in\mathbb{R}^+$ is
$$
P = IV.
$$
Now the current is given as an (alternating) current density $J(\mathbf{x},t)=\Im(e^{i\...
- 21
1
vote
2
answers
4k
views
Which expression to use for electrical power?
We know that electric power can be written as $P=VI$, or $P=\frac{V^2}{R}$, or $P=I^2R$.
But when to use which one? Sometimes two different formulas give different results! Please explain with some ...
- 3,400
0
votes
2
answers
1k
views
Does a switched on power socket consume electricity? [closed]
Lets say I have a TV and a power socket but the TV switch is off however the socket switch is switched on, so will it consume electricity?
1
vote
3
answers
502
views
Electric Power $P$
In my textbook there are 2 formulas for electric power:
$$\begin{array}{cccr}
P &=& E/t &\hspace{10pt} (1) \\
P &=& VI. &\hspace{10pt} (2)
\end{array}$$
What is the ...
- 60.3k
0
votes
1
answer
50
views
Computing power based on weighted averages [closed]
I'm struggling to understand the reason why I'm getting different results with two apparently similar ways to compute the power consumption (over multiple time intervals) of an electrical circuit.
...
- 6,198
1
vote
2
answers
685
views
Calculate power $P=V \times I$
I have an adapter which mentions like this...
Input: 100-240V~1.8A
50-60hZ
So how much power does it really consume?
I just knew ...
- 213k
1
vote
5
answers
1k
views
How do electrical devices suck electricity?
If the electric potential is 220V and some device needs 1500watts then how does it suck exactly that amount of electrical energy from outlet?
- 5,649