(a) 25lx
(b) 11.11lx
<u>Explanation:</u>
Illuminance is inversely proportional to the square of the distance.
So,
where, k is a constant
So,
(a)
If I = 100lx and r₂ = 2r Then,
Dividing both the equation we get
When the distance is doubled then the illumination reduces by one- fourth and becomes 25lx
(b)
If I = 100lx and r₂ = 3r Then,
Dividing equation 1 and 3 we get
When the distance is tripled then the illumination reduces by one- ninth and becomes 11.11lx
The fraction of radioisotope left after 1 day is , with the half-life expressed in days
Explanation:
The question is incomplete: however, we can still answer as follows.
The mass of a radioactive sample after a time t is given by the equation:
where:
is the mass of the radioactive sample at t = 0
is the half-life of the sample
This means that the mass of the sample halves after one half-life.
We can rewrite the equation as
And the term on the left represents the fraction of the radioisotope left after a certain time t.
Therefore, after t = 1 days, the fraction of radioisotope left in the body is
where the half-life must be expressed in days in order to match the units.
Learn more about radioactive decay:
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