Physics Power Q (1 Viewer)

[Shoom]

Calculate the resistance of a 100W light globe connected to a mains voltage of 240v

Calculate the energy consumption in kilowatt-hours if the 100w globe is on for 10minutes. PLEASE SHOW ALL WORKING.

Thanks

How much energy will a 400w hair dryer consume if it is used constantly for 5 min

E=Pt
= 400x5

why does my text book have 400x5x60j?

 

[kaz1]

1. P=V²/R
100=240²/R
100=57600/R
R=576 ohms

3. It says that in your textbook because power is Joules per second, hence you multiply by 60.

 

[kaz1]

Lol I forgot the second question.
1 kwh = 3600W
100 x 10 x60=60000J
60 000/3600=16.67kWh.

I think that is right. I am a bit hazy on kWh.

 

[Twickel]

Could you try the ergy consumption bit,

You know the Jacaranda textbook why do they never use I^2 R or V^2/r they alway try and find either the resistnace or current using r=v/i then sub into p=vi. When I try use V^2/r it answer is different.

 

[ratcher0071]

Calculate the resistance of a 100W light globe connected to a mains voltage of 240v

Calculate the energy consumption in kilowatt-hours if the 100w globe is on for 10minutes. PLEASE SHOW ALL WORKING.

Thanks

How much energy will a 400w hair dryer consume if it is used constantly for 5 min

E=Pt
= 400x5

why does my text book have 400x5x60j?

1)
P=V^2/R
R=V^2/P
R=240^2/100
R=576 ohms

2)
Energy (kWh)=Power (kW) x time (h)
Energy (kWh)= (100/1000) x (10/60)
Energy (kWh)= 0.1 x (1/6)
Energy (kWh)= 1/60 kWh
Energy (kWh)= 0.017 kWh

3)
Energy (J)=Power (W) x time (s)
Energy (J)= 400 x (5 x 60)
Energy (J)= 400 x 300
Energy (J)= 120000 Joules
Energy (J)=120 KJ

 

[ratcher0071]

Lol I forgot the second question.
1 kwh = 3600W
100 x 10 x60=60000J
60 000/3600=16.67kWh.

I think that is right. I am a bit hazy on kWh.

1 kWh=3 600 000 J

 

[Aerath]

2)
Energy (kWh)=Power (kW) x time (h)
Energy (kWh)= (100/1000) x (10/60)
Energy (kWh)= 0.1 x (1/6)
Energy (kWh)= 1/60 kWh
Energy (kWh)= 0.017 kWh

I got this answer, as opposed to kaz1's answer.