# Search results

1. ### 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...
2. ### 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...
3. ### 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
4. ### 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...
5. ### 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...
6. ### 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...
7. ### 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...
8. ### 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...
9. ### 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...
10. ### Microphone - transistor switching on a led

hi i want to use a microphone connected to the base of a transistor.yhe transistor should work as a switch . it should turn on with a sound to the micro phone. does anyone know what voltage the mic can produce?what kind of microphone do i need and what kind of transistor?the circuit is designed...
11. ### Transistor as a switch

Hi guys, i want to fix a circuit that will use a led and i want to use a transistor as the switch to the led. I would like the base current to be produced by a sound played throug ha mobile. A sound turning the light on and the same or other sound turning it off. No ideas how to do it.Thank you...