Irradiance

Question 1

what is irradiance?

Answer 1

a measure of how much power is incident per area of surface.

Question 2

surface area of a sphere formula

Answer 2

A=4 pie r squared

Question 3

example of source with high irradiance

Answer 3

lasers

Question 4

example of source with low irradiance

Answer 4

light bulbs

Question 5

why is the irradiance of a light bulb low?

Answer 5

light bulbs radiate energy in three dimensions in order to light up a room and therefore the irradiance at a point in the room is very small.

Question 6

what is a point source?

Answer 6

emits light in all directions (emits isotropically)

Question 7

what is a laser source?

Answer 7

doesn’t follow inverse square law at is spreads out.

Question 8

the further away you are from a source…

Answer 8

…the less the irradiance

Question 9

if you double the distance, the irradiance…

Answer 9

…falls by a factor of 2 squared = 4

Question 10

what does the graph of irradiance against distance look like?

Answer 10

a curve sloping down

Question 11

what is needed in order to write an equation for a relationship?

Answer 11

a graph with a straight line through the origin

Question 12

three ways of improving irradiance experiment?

Answer 12

1. smaller lamp
2. black cloth on bench
3. take place in a darkened room

Question 13

how does using a smaller lamp improve the experiment?

Answer 13

more like a point source

Question 14

how does using a black cloth on the bench improve the experiment?

Answer 14

reduces/prevents reflections

Question 15

steps for proving inverse square law

Answer 15

1. obtain values of irradiance for different distances
2. plot graph of I against 1/d squared
3. if graph is straight line through the origin this verifies inverse square law.
   or
   if values for I x d squared are constant