The time required for making a print a distance of 0.25 m from a 60 W lamp is 5 s. If the distance is increased to 40 cm, the time required in second to make a similar print is

Question

Dr. Abubacker · Accepted Answer

(c) $\frac{I}{r_{1}^{2}}t_{1} = \frac{I}{r_{2}^{2}}t_{2} \Rightarrow t_{2} = \frac{r_{2}^{2}}{r_{1}^{2}}t_{1} = \left( \frac{40}{25} \right)^{2}s = \left( \frac{8}{5} \right)^{2}s = \frac{64}{5}s = 12.8\ s$

Q. The time required for making a print a distance of 0.25 m from a 60 W lamp is 5 s. If the distance is increased to 40 cm, the time required in second to make a similar print is

Explanation

Reviewed by Dr. Abubacker

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