level: Inverse Square Law
Questions and Answers List
level questions: Inverse Square Law
| Question | Answer |
|---|---|
| what is irradiance | power per unit area the amount of light energy incident on each square metre of a surface per second |
| what is irradiance measured in | watts per square metre (Wm-2) |
| what is the formula for irradiance | I=P/A where I is irradiance in Wm-2 P is power in W A is Area in m^2 |
| When is a light considered a point source | if it emits light equally in all directions in three dimensions, creating a sphere around the light source the source doesn't have to be small, but its size must be small in comparison to the distance from the observer to the source |
| what is the formula for irradiance when it is measured at different distances from the source | I₁(d₁)²=I₂(d₂)² where I1 is irradiance at point 1 in Wm-2 I2 is irradiance at point 2 d1 is distance to point 1 in m d2 is distance to point 2 in m |
| what does the graph of irradiance against distance look like | ... |
| what does the graph of I against 1/d² look like | irradiance is directly proportional to 1/d² therefore I=k/d² and Id²=k (where k=constant) |
| "describe how this apparatus could be used to verify the inverse square law for a point source of light" | obtain values of irradiance for different distances plot a graph of I against 1/d^2 graph should be a straight line through the origin if the light is a point source |