Give the function of the lamp lens and micro scope in the Brownian motion
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Answer:
I first remember being shown Brownian motion in high school by the physics teacher using a microscope to observe smoke particles suspended in air in a glass cell. This is one of a number of recommended ways of demonstrating this classic experiment; others include observing aqueously suspended fine particles such as pigments (e.g. Gamboge, Indian ink) or fat globules in very dilute milk (refs. 1 - 3). Robert Brown studied the motion after whom it takes its name, in tiny particles released from the medium within pollen grains
I was browsing eBay recently and noticed a used Brownian motion smoke cell which I purchased for a few pounds as was interested in comparing its effectiveness with other techniques tried; my preferred method as a hobbyist is to use extremely dilute milk as it is effective and fairly easy to set up.
The smoke cell purchased was the 'Whitley Bay' pattern made by Griffin & George Ltd, which seems a popular design and is still available new from educational suppliers. There has been speculation online as to why it was apparently named after a small town on the north east coast of England (ref. 5). Was the designer based there; or perhaps an allusion of the smoke cell's lighting to the town's offshore lighthouse? I'd be interested to hear from any reader who knows why.
The cell is shown below. It is essentially a self contained lamp, lens and smoke cell to observe the bright smoke particles under a microscope against a dark background. It uses the 'festoon' type bulb* 12V 3W, to shine light through a solid glass rod to give a thin beam of light in the small cell. As smoke particles pass through this beam the particles are seen as white specks undergoing motion, both Brownian and other motion like convection. *The bulbs are readily available as they are used in e.g. some older car door courtesy lamps.