Burning wood with a magnifying glass requires concentrating sunlight through the glass down to the smallest point possible. It helps to have material such as paper or dry grass to use as tinder.
Starting fires with a lens is not only a backyard science that many experiment with as children, but It is also a valuable survival tactic. When matches or lighters are unavailable, a curved piece of glass is useful for creating fire. The method requires trial and error, but under the right conditions, fire can be produced.
Tilt the glass at an angle to focus a single, small beam of light. Next, place the tinder in the concentrated spot of sunlight and wait for a flame to catch. Once the tinder begins to smoke and catch fire, transfer the spark to a larger piece of dry wood.
A magnifying lens is not essential to this method of fire-starting, as any curved glass works. Binoculars, glass bottle bottoms and even light bulbs are useful. If there is difficulty creating a flame, placing a small drop of water on the glass helps to concentrate the light.
This experiment is a testament to the danger of refuse left outdoors. Bottles and broken light bulbs can pose a fire hazard, especially during dry conditions.