First slide

Radiation

Question

Two spheres P and Q, of same colour having radii B cm and 2 cm are maintained at temperature 127°C and 527°C respectively. The ratio of energy radiated by P and Q is

Easy

A

0.054
B

0.0034
C

1
D

2

Solution

$\begin{array}{l} Q \propto T^{4} r^{2} \\ ∴ \frac{Q_{1}}{Q_{2}} = \frac{T_{1}^{4} r_{1}^{2}}{T_{2}^{4} r_{2}^{2}} = \frac{(400)^{4} \times (0 \cdot 08)^{2}}{(800)^{4} \times (0 \cdot 02)^{2}} = 1 \end{array}$

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