The intensity on a screen 20 ft from the light will be 0.125-foot candles.
<h3>What is the distance?</h3>Distance is a numerical representation of the length between two objects or locations.
The intensity I of light varies inversely as the square of the distance D from the source;
I∝(1/D²)
The ratio of the intensity of the two cases;
Hence, the intensity on a screen 20 ft from the light will be 0.125 foot-candles
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Answer:
option (c) is correct
Explanation:
Half life of a substance is the time in which the element becomes half of is initial value.
half life, T = 8 days
Amount remaining, N = 10 % of original value
Let the original value is No.
N = 10% of No
N = 0.1 No
Let the time taken is t and the decay constant is λ.
The relation between the decay constant and the half life is given by
Us the equation of radioactivity
Taking natural log on both the sides, we get
0.08664 t = 2.303
t = 26.6 days