# Enery phisic question

#### RMHAZARD

hi here is the question

A 60 watt light bulb is left swithed on for 10 hours. If the light bulb is 15% effcient, calculate the amount of light energy produced in that time. what is the total energy consumption of the light bulb in this time.

so i need to find work done right so is that power divided by time to get the energy and then find 15% of that am i right i am bathed by this.

#### Kurdt

Staff Emeritus
Gold Member
A watt is 1 unit of energy per unit time. You know how much of the energy was turned into light (15%) and the length of time the light was left on. No need to introduce work.

#### RMHAZARD

so do i divide watts by time taken?

#### RMHAZARD

so 60 watts divided by10 hours which is 6 15% of 6 is 0.9 if i am correct

can you please tell me if i am right if not can you advive me where i went wrong

#### Kurdt

Staff Emeritus
Gold Member
your answer is incorrect. First you need to think about units
watts is per second whereas you're given a time in hours. Secondly do you think the energy would be lower or higher than how much you are using in one second?

#### RMHAZARD

so 10 hours is 600 minutes 36000 seconds and 60 watts goes goes in in 36000 2160000 so 15% 324000 am i right

#### Kurdt

Staff Emeritus
Gold Member
Correct. now remember to state you units. energy is measured in.....

### The Physics Forums Way

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving