# Calculate Power Consumption: 600W Device at 220V to 160V | 1W Precision

• chawki
In summary, the conversation discusses a problem where an electrical device consumes 600 W of power at 220 V and the task is to calculate its power consumption at 160 V with a precision of 1 W. The solution involves finding the current and resistance and using the equation W=V^2/R to determine the power consumption. Ultimately, the correct answer is found to be 317 watts. There is also a discussion on rounding and significant digits in the intermediate results.
chawki

## Homework Statement

An electrical device consumes 600 W of power, when connected to 220 V voltage.

## Homework Equations

Calculate the power consumption of the device, when it is connected in 160 V voltage. Give the answer in 1 W precision.

## The Attempt at a Solution

I tried and found I=2.72 amps, R=80.88 Ohms, and W=316.51

Looks good.You need to round up the final answer and for problems of this type it's probably best to do the rounding up at the end.

hi chawki!
chawki said:
I tried and found I=2.72 amps, R=80.88 Ohms, and W=316.51

yeees

but now do it the quick way (ie, without bothering to find I or R)

when you vary V, what is Q proportional to?

Oh please Tiny-Tim...don't tease me on this one too

317?

write out all the equations (for W V I and R) …

eliminate I (since you don't know what I is), that should give you just W V and R …

then assume that R is constant …

how does W depend on V ?

W=V^2 / R
But what does it have to do if it is proportional to V^2

if W = V2/R

and if V is decreased from 220 to 160 (and R stays the same) …

how much is W increased?

i give up

Is it 317watts ?

It is said to give the answer in 1watt precision

Last edited:

since there is .51 the answer would be 317watts?

Yes. And even more so if you do not make that rounding error in the current.

ehild

We need to round also the current??

You rounded it to 2.72. It is wrong. It was 600/220=2.727272~2.727 A. The resistance is 220/2.727=80.67 ohm.

You should use at least one more significant digits in the intermediate results than in the final result.

ehild

## 1. How do I calculate watts?

To calculate watts, you can use the formula: watts = volts x amps. This means that if you know the voltage and amperage of a circuit, you can multiply them together to find the wattage.

## 2. What is the unit of measurement for watts?

The unit of measurement for watts is W (or kW for larger values). This represents the rate at which energy is being used or produced.

## 3. What is the difference between watts and watts per hour?

Watts (W) represent the amount of power being used at a specific moment, while watts per hour (Wh) represent the amount of energy used over a period of time. To calculate watts per hour, you would need to know the wattage and the time period.

## 4. Can watts be converted to other units of power?

Yes, watts can be converted to other units of power such as horsepower (hp) or British Thermal Units (BTU). There are conversion calculators available online to help with these conversions.

## 5. How do I calculate watts for an AC circuit?

To calculate watts for an AC (alternating current) circuit, you would need to take into account the power factor, which represents the efficiency of the circuit. The formula for calculating watts in an AC circuit is: watts = volts x amps x power factor.

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