Irradiance Flashcards

1
Q

what is irradiance?

A

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

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2
Q

surface area of a sphere formula

A

A=4 pie r squared

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3
Q

example of source with high irradiance

A

lasers

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4
Q

example of source with low irradiance

A

light bulbs

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5
Q

why is the irradiance of a light bulb low?

A

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.

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6
Q

what is a point source?

A

emits light in all directions (emits isotropically)

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7
Q

what is a laser source?

A

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

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8
Q

the further away you are from a source…

A

…the less the irradiance

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9
Q

if you double the distance, the irradiance…

A

…falls by a factor of 2 squared = 4

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10
Q

what does the graph of irradiance against distance look like?

A

a curve sloping down

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11
Q

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

A

a graph with a straight line through the origin

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12
Q

three ways of improving irradiance experiment?

A
  1. smaller lamp
  2. black cloth on bench
  3. take place in a darkened room
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13
Q

how does using a smaller lamp improve the experiment?

A

more like a point source

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14
Q

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

A

reduces/prevents reflections

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15
Q

steps for proving inverse square law

A
  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
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