The hair straighteners have a power of 90 W.
What is meant by a power of 90 W?
and..
Calculate how many kilowatt-hours of electricity are used when the straighteners are used for 15 minutes?
Write down the equation you use. Show clearly how you work out your answer and give the unit.
we were not taught how to do it properly and i have been stuck on this question for 30 minutes : O hellpp!!!
What is meant by a power of 90 W?
and..
Calculate how many kilowatt-hours of electricity are used when the straighteners are used for 15 minutes?
Write down the equation you use. Show clearly how you work out your answer and give the unit.
we were not taught how to do it properly and i have been stuck on this question for 30 minutes : O hellpp!!!
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The supplied electricity is 90 watts
90x15/60 = 22.5 kilo watt-hours
90x15/60 = 22.5 kilo watt-hours
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W = watt is the unit of power (= energy/time)
Hence 1 W means 1 joule of work is done in 1 second.
90 W means 90 joule of work is done in one second.
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Kilowatt-hours short form is kWh.
Kilo means 1000
watt means 1 joule/second/
kWh = 1000* 1 joule/second * 1 hour.
We know 1 hour = 3600 second.
Hence
1kWh means 1000* 1 joule/second * 3600second.
Seconds get cancelled and we are left with
1kWh means 3600000 joule
Note joule is the unit of energy.
Hence
1 kWh is another unit of energy and = 3600000 joule.
============================
In the problem a 90 W heater is used for 15 minutes.
Energy = power * time
First convert 90W into kilo watt = 90/1000 = 0.09 kW.
Then express 15 minutes in hours = 15/60hour = 0.25 h.
Energy = power *time = 0.09 kW.* 0.25 h. = 0.0225 kWh.
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Or if we want the energy in terms of joules,
15 minutes = 15*60 = 900 seconds
Energy = Power * time = 90 (joule/second) * 900 second
= 81000 joule.
=====================
Note that 0.0225 kWh. = = 81000 joule
=========================
Hence 1 W means 1 joule of work is done in 1 second.
90 W means 90 joule of work is done in one second.
==============================
Kilowatt-hours short form is kWh.
Kilo means 1000
watt means 1 joule/second/
kWh = 1000* 1 joule/second * 1 hour.
We know 1 hour = 3600 second.
Hence
1kWh means 1000* 1 joule/second * 3600second.
Seconds get cancelled and we are left with
1kWh means 3600000 joule
Note joule is the unit of energy.
Hence
1 kWh is another unit of energy and = 3600000 joule.
============================
In the problem a 90 W heater is used for 15 minutes.
Energy = power * time
First convert 90W into kilo watt = 90/1000 = 0.09 kW.
Then express 15 minutes in hours = 15/60hour = 0.25 h.
Energy = power *time = 0.09 kW.* 0.25 h. = 0.0225 kWh.
----------------
Or if we want the energy in terms of joules,
15 minutes = 15*60 = 900 seconds
Energy = Power * time = 90 (joule/second) * 900 second
= 81000 joule.
=====================
Note that 0.0225 kWh. = = 81000 joule
=========================
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W = Watts
This is (put simply) the unit we use to measure electricity.
The hair straighteners need 90 watts to power them.
To get to kilowatt-hours from here we need to convert to kilowatts
1000 W = 1 KW
90 W = 0.09 KW
What we do next is simple.
KW x time = kilowatt-hours
our time is 15 minutes which is one quarter of an hour.
so
0.09KW x 0.25h = 0.225
The answers is 0.225 kilowatt-hours
I hope i explained it well.
-Turquoise
This is (put simply) the unit we use to measure electricity.
The hair straighteners need 90 watts to power them.
To get to kilowatt-hours from here we need to convert to kilowatts
1000 W = 1 KW
90 W = 0.09 KW
What we do next is simple.
KW x time = kilowatt-hours
our time is 15 minutes which is one quarter of an hour.
so
0.09KW x 0.25h = 0.225
The answers is 0.225 kilowatt-hours
I hope i explained it well.
-Turquoise
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The straighteners do not have a power of 90W
They are designed to use 90W of power.
Watts is obtained by multiplying the numerical value we give to current, by the numerical value we give to voltage W = IV
90W in an hour would be 0.09kWH
Divide that by 4 (i.e. 15 minutes) is 22.5mWh or 0.0225kWh
They are designed to use 90W of power.
Watts is obtained by multiplying the numerical value we give to current, by the numerical value we give to voltage W = IV
90W in an hour would be 0.09kWH
Divide that by 4 (i.e. 15 minutes) is 22.5mWh or 0.0225kWh
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means he has to do 90J work in 1sec
2.
kwhr= (Device wattage/1000) * the time of usage in hr
kwhr= (90w*15)/(1000*60)=0.0225 kwhr
2.
kwhr= (Device wattage/1000) * the time of usage in hr
kwhr= (90w*15)/(1000*60)=0.0225 kwhr