# Search results

1. ### Activated speed

my problem is that for the second question i calculate the new pressure of the air inside the tube but since i do not know the consistency of the air at that temperature how can i find the effective speed.?(hope it is the correct term) And also at the first question i do not know the starting...
2. ### Activated speed

sorry but my english are not so good.does the term effective speed helps?or else i want to find the square root of the average values of speed square.i am not sure how is ti called in english.
3. ### Activated speed

in adition for the activated speed i have to know the pressure and the concentration of the air in order to calculate it?
4. ### Activated speed

thanks for your help.one question.at the first question when you say that the N changes what do you mean?how can the amount of moles inside the tube change because of the heating of the tube?

6. ### Activated speed

i was thinking about the above problem for the first question to simply calculate the new V of the air assuming that the pressure is constant before and after the heating and that the pressure equals i atm same as the one existing in the atmosphere.then if i use that the consistency of air is...
7. ### Activated speed

Hi to you all.i have an exercise i cannot solve.i think something is missing. Cylindrical tube V=10L opened at the top has air with a temperature of T1=27 oC.We provide heat to the tube until the temperature reaches the value of T2=327 oC.A)we have to find the amount of air that leaves from...
8. ### Activated speed

Hi to you all.i have an exercise i cannot solve.i think something is missing. Cylindrical tube V=10L opened at the top has air with a temperature of T1=27 0C.We provide heat to the tube until the temperature reaches the value of T2=327 oC.A)we have to find the amount of air that leaves from...
9. ### Finding the size of a photographed image

at a distance of 12,673m it captures an object with length of 10,350m.so i found that tha fov is 44 degrees.i think i am right no?thyanks
10. ### Finding the size of a photographed image

hi again.please help.in order to find the FOV of the camera does the capture photo has to be always in focus?because i have taken a fiew measurements and not all were in focus.then i calculated the FOV as the average value of the field of view of each.please help
11. ### Finding the size of a photographed image

may be you used the entire width of the picture provided?because a divided with two in order to obtain have of it for my calculations.then the angle i double it
12. ### Finding the size of a photographed image

actually i have doubled it.may be the reason is that i use a mobile for the capturing of the images?
13. ### Finding the size of a photographed image

thanks.one last question.how did you find the field of view that is 80 degrees?i found it around 44 degrees.thanks
14. ### Finding the size of a photographed image

this foto is when the object is at three cm away from camera.it is blurry because i have added a lens that is blury in front of the camera.i only care for an aproximation of the distances.thanks
15. ### Finding the size of a photographed image

to tell yo the truth i am completely confused.i have a mobile camera.the resolution of the photos it captures is 640x480.what does this mean?that on the horizontal axis it uses640 pixels and on the vertical 480 pixels.am i right?since i know that the actual width of the object, lets say a wall...
16. ### Finding the size of a photographed image

Hi.no i do not measure the width on the monitor.i have performed an experiment and have calculated the horizontal FOV.From the Horizontal FOV i have calculated the actual width of the captured object not from the monitor.as i do not know the vertical FOV i want to use the ratio 480/640 to...
17. ### Finding the size of a photographed image

Thank you for your time. I understood what you say.but i am thinking that the ratio of the pixels per cm horizontally to the pixels per cm vertically should be the same since the same screen is used. So the ratio would not be constant whatever screen i use?
18. ### Finding the size of a photographed image

thanks.i am not sure i understood your answer.do you mean that the ratio of the pixels reflect also the ratio between the width and the height of the object captured?thank you very much and i am sorry
19. ### Finding the size of a photographed image

Hi. i have a photographic camerawith a resolution of 640x480.i know that at the focus point the object photographed has a length of 2 cm.i want to find the height h of the object.i was thinking that the ratio h/length would equal the ratio 480/640.am i right?thank you
20. ### Field of view

yes i did but you confused me a little bit with the number of pints.and since i did not get any other replies i post it again!thanks
21. ### Field of view

Hi.i have a question about Field of view. I know that it is an angle showing on a triangle.inside the area of the triangle any object can be photographed .am i right?i know tha it is not a scientific explanation, i am just saying what i have understood. i have a camera. I do not know the...
22. ### Field of view enquiry

i wrote it again because at the first message i had done many mistakes .sorry Hi.thanks about my question on focal length.you were really helpful.Another question now about Field of view. I know that it is an angle showing on a triangle.inside the area of the triangle any object can be...
23. ### Field of view enquiry

Hi.thanks about my question on focal length.you were really helpful.Another question now about Field of view. I know that it is a angle showing a triangle.inside the area of the triangle any object can be photographed .a i right?i know tha it is not a scientific explanation iam just saying...
24. ### Lens enquiry- focal length

Hi .I am reall y confused about the focal length of lens.i understand that it is the length from the lens to the point where parallel beams coming from infinity after passing through the lens cross one each other.My question ,knowing thew focal length wher exactly does it help?does it have any...
25. ### Transistor as switch-op amp voltage amplifier?

Hi can anyone explain to me how you can drive a transistor to function as a switch?what calculations i have to make in order to decide the type of transistor that i need and the kind of resistors that i need. also i have a voltage of maximum 80 mv.i want to enlarge it in order to drive the...
26. ### Handsfree enquiry

transistors enquiry Hi. i played a sound on the handsfree of the mobile and i was able to take a waveform.the maximum value of voltage that i get is 80 mv. can you explain me how do i have to connect the transistor in order to function as a switch?i tried yesterday but it did not work.the...
27. ### Handsfree enquiry

earphone characteristics thank you for your reply berkeman.the problem is that i do not know much about electronics.Decay time i guess you mean the time i want the led to be turned on.The perfect situation would be the led to be turned on with a sound and then turned off with another sound.The...
28. ### Handsfree enquiry

thank you berkeman.is it possible to draw may be a sketch of the circuit you described?thanks
29. ### Handsfree enquiry

hi . I am trying to construct a circuit to light a white led.i want to use as a switch a transistor. i intend to take the voltage required between the base and the collector of the transistor from the handsfree slot of the mobile ericsson p800. i bought the hndsfree of the mobile, cut one of...
30. ### Led enquiry

hi i have fixed a simple circuit for lighting up a led.i have included a potentiometer. as the led is white i know that the voltage drop of the led is around 4v.when the potentiometer is at min resistance the voltege drop is actuallu around 3.8v.the problem is that when i turn the potentiometer...