Recent content by Howlin

Hi all, I want to calculate the perceived height of a number of mountains. I know the height and distance from one of the mountains. If the hieght of the mountain is 925 metres and the distance is 20000 metres away, is there a method of calculating the perceived height for this mountain and...

Hi Baluncore, Thank you for the reply. Do you know of any studies or publications that indicate an appropriate percentage heat gain percentage from LED lighting? I have found some but they don't mention what percentage of the say 80 watts would be lighting and what % would be heat gain.

Hi all, If in a room, a lighting design was carried out and the room will contain 4 no, LED luminaries with a total wattage of 80. My query relates to what would a reasonable figure or percentage be to use as heat gain from the light. Of the 80 watts, how much of it would go into heat? I am...

Hi all, I have a copper pipe which has 15mm of insulation on it. The outside radius of the pipe is 17.2mm and the inside radius is 14.8mm. The insulation will have a conductivity of 0.025. I found an question which is meant to show an equation for the heat loss in an Insulated Cylinder or...

I think i worded that incorrectly. It is assumed that the incoming mains water has a temperature of 10 degrees. The 6.967 kWh is the energy required to initially heat the tank from cold to 60 degrees. That figure would not represent a per day figure as the heat loss to the environment and the...

Hi, If it is assumed the temperature of a shower is to be 43°C and the electric shower consumes 50 litres of water at that temperature, then the Energy required for an electric shower would be: QElectric Shower = mcΔT QElectric Shower = 50 * 4.181 * (43-10) QElectric Shower = 6.89945 kJ or...

Hi all I have the following question that I require help with. 1. Homework Statement A supply fan must deliver 2.5m3s of air against a system pressure of 500 Pa.The selected fir this has a performance characteristic as listed below when running at a speed of 1800 revs/min. i) Plot the system...

Thank you, this is what I needed. Luminance = incident illuminance/2π (assuming it is perfectly diffused) But if it isn't perfectly diffused Luminance = Incident illuminance * a diffusion factor / 2π I have tried to look for the BRDF for a standard (if there is even such a thing) rough diffuse...

I am not asking about the classes. I just mentioned them to give a back round on what I was wanting. All I want to know is: Is there an easy way of converting luminance to illuminance or illuminance to luminance?

Hi all, I am not sure this is meant to be a part of the forums but if it is to be changed, please let me know. This is not a homework question but more of a (weird) curiosity question. I was looking at the different lighting classes that are out there for roads and have noticed that the...

Homework Statement Which of the folowing decays are forbidden by C-iinvariance ω° = π° + γ η' = ρ° + γ π° = γ +γ + γ Homework Equations None The Attempt at a Solution The answers are meant to be: ω° = π° + γ -1 : (+1) (-1) -> Allowed η' = ρ° + γ +1 -> (-1) (-1) ->...

Homework Statement The average energy of a harmonic oscillator is written using Boltzman statistics as: <ε> = (<n> +.5) = \frac{\sum_{n} ε_{n} exp \frac{-ε_{n}}{kt}}{\sum_{n} exp \frac{-ε_{n}}{kt}} Expand the expontentials and hence derive the Planck Occupancy <n> = n(ω,T)...

Homework Statement Assume you have 6 white pine boards with all the same breaking force and there is no difference in the boards at all If you find the force to break one pine board, two pine boards with no gaps and three pine boards on top of each other with no gap. Does the amount of...

Hi I have been doing taewkon do and seen people break boards and I want to know is it easier to break say 1 2 inch thick pine board or 2 1inch pine boards assuming that the boards are uniform and have no knots in them and that the 2 1 inch boards are on top of each other with no gap...

But why would it be higher, shouldn't it be just the same force required to break the boards or glass, no matter if it is hit fast or slow?