Answer:
The light intensity is 528 foot-candles at 5 feet
Step-by-step explanation:
<em>If x and y are in </em><em>inverse variation</em><em>, then </em><em>x y = k</em><em>, where k is the constant of variation</em>
In the given question
∵ The intensity I, of light received at a source, varies inversely as the
square of the distance d, from the source
→ That means I × d² = k, where k is the constant of variation
∴ I × d² = k
∵ I = 33 foot-candle at d = 20 feet
→ Substitute them in the rule above to find k
∴ 33 × (20)² = k
∴ 33 × 400 = k
∴ 13200 = k
→ Substitute the value of k in the equation
∴ I × d² = 13200 ⇒ equation of variation
∵ d = 5
→ Substitute it in the equation to find I
∵ I × (5)² = 13200
∴ I × 25 = 13200
→ Divide both sides by 15
∴ I = 528
∴ The light intensity is 528 at 5 feet
