If i use 7.5watts of electricity at home constantly for a month how much would it cost per month?

Question

I bought a plug-in pest repellent. It claims to only cost pennies a month to use. I was wondering if anyone knew how to calculate it. The provider we use scottish power and the device claims to be 7.5watts , but doesn't have any amp/voltage figures on it.
It'll be on constantly, how much will it cost?
Also, does anyone know if these things are any good? It's a Viatek dual technology one that uses electromagnetic and ultrasonic technology

Answer 1

electricity suppliers charge by the kilowatt-hour
so a device using 1 kw for 1hour uses 1 unit
yours would take 1000/7.5 hours to use 1 unit. you would have to find the cost of a unit from your supplier (look at your last bill), but its probably not far from 10p

and i used a plug in mosquito repellent on holiday and i thought it worked very well. better than those god-awful anti-malarial tablets by a long way. they gave my friend panic attacks. and the local hospital said they prefer tourists not to take the tablets as they make detecting malaria more difficult

Answer 2

Your home energy usage is usually calculated in terms of kilowatt-hours. Your electric bill should tell you how much each kilowatt-hour of energy costs you (typically it's something like 10 cents).

A kilowatt is the same as 1000 watts. So to calculate how many kilowatt-hours of energy is used by an appliance in a certain number of hours, convert its power rating to kilowatts, then multiply it by the number of hours of usage.

Your pest repellent uses 7.5 watts, which is 0.0075 kilowatts.

There are (roughly) 720 hours in a month.

So in one month your pest repellent uses this much energy:

(0.0075 kW)(720 hrs) = 5.4 kilowatt-hours.

Next, multiply that by the cost per kilowatt-hour that your electric company charges.

Answer 3

Well you need to know how much they charge you for a kw hour. Or possibly they charge you by the joule but your kw hour for that device for a 30 day month would be 5.4 so that should not be so expensive. It would consume 19.44 mJ if that is how they charge you.

Answer 4

if you are using scottish power as a supplier then i assume you are on 240v supply
that would give you a current of about 0.03 amps so the statement by them is true.
as for if they work or not well if it does not work sue the company for false advertising