is there a way to measure roughly the light intensity coming out of a torch in a dark room? preferably without a light meter
Ya, if lights intensity is large den, electrons pulled out of a matel will be of large quntity. Bcaz intensity of light is directly proportional to rate of emission of electron.
unless you have photo detector you can't measure its intensity. just think of how you will measure how much intense its is. is it greater than candle light or dimmer than bulb?.. only photo detector can show you the intensity magnitude. it basically counts the number of electron falling on it per second.
This is the more scientific explanation : If u see an Arc from an Arc welder on TV you will see just a white spot . Colors in Television are generated using an electronic command , each color has a specific voltage witch translates into photons that your eyes detect . The TV set emits a white level that is calculated so your eyes don't get damaged from the photon quantity that the TV set radiates . That means that no matter how bright the real Arc is, generating a high quantity of photons that damages your retina , on TV there is a limit to the intensity of light . The color white (witch isn't a color actually) has the highest voltage command (about 1V) but just replicates the Arc scaling back the intensity of light . What colors and images you see an TV are newer the same as in real life , these are synthetic colors made by electrons stimulating (hitting) a Luminophore. The easy explanation: The brightest color you see on any display is limited so that your eyes don't get damaged . The image stays on your retina till it heals the damage. (that's why you see it when you close your eyes ) .
In regard to Anal kumar S method of using photoelectric effect to help determine the intensity, I think it is not a good way to determine the intensity of the light from the torch. The type of metal emitter used is important as if the light from the torch, being not monochromatic, have certain light with a frequency below the thrash old/cutoff frequency of the metal, then that frequency of light is as good as useless. Furthermore, this experiment is hard to carry out. The collector plate will not be able collect most of the photoelectric electrons as the electrons will ionise the nearby air particles. This will affect the current measured and the intensity of light measured will carry a large percentage error. The way to prevent this is to conduct the experiment in a vacuum container. Also, the current measured will most likely be small due to the relatively low frequency of the light from a normal torch. A very sensitive ammeter is needed to detect the current. However, I am not able to think of better ways to measure the intensity :p. Maybe use a spectrometer or use a light dependent resistor and, of course, you need to know the characteristic of the resistor.
