If 5% of the energy supplied to a bulb is irradiated as visible light, how many quanta are emitted per second by a 100 W lamp? (Assume wavelength of visible light as 5.6 × 10 - 5 cm)

Question

If 5% of the energy supplied to a bulb is irradiated as visible light, how many quanta are emitted per second by a 100 W lamp? (Assume wavelength of visible light as 5.6 × 10 - 5 cm) (A)  1.4 × 10 19  (B)  3 × 103 (C)  1.4 × 10 - 19  (D)  3 × 104

Tardigrade Admin · Accepted Answer

Energy radiated as visible light = ( 5/ 100) × 100 = 5 J/s Let n be the number of photons emitted per second. Then, nhv = E = 5 ∴ n = ( 5 λ / hc ) = ( 5 × 5.6 × 10 - 7 / ( 6.62 × 10 - 34 ) ( 3 × 108 ) ) = 1.4 × 10 19

Q. If 5% of the energy supplied to a bulb is irradiated as visible light, how many quanta are emitted per second by a 100 W lamp? (Assume wavelength of visible light as $5.6 \times 1 0^{- 5}$ cm)

$1.4 \times 1 0^{19}$

$3 \times 1 0^{3}$

$1.4 \times 1 0^{- 19}$

$3 \times 1 0^{4}$

Energy radiated as visible light = $\frac{5}{100} \times 100 = 5$ J/s
Let n be the number of photons emitted per second. Then,
nhv = E = 5
$∴ n = \frac{5 λ}{h c} = \frac{5 \times 5.6 \times 1 0 ^{- 7}}{( 6.62 \times 1 0 ^{- 34} ) ( 3 \times 1 0 ^{8} )}$
= $1.4 \times 1 0^{19}$

Q. If 5% of the energy supplied to a bulb is irradiated as visible light, how many quanta are emitted per second by a 100 W lamp? (Assume wavelength of visible light as 5.6×10−5 cm)

1.4×1019

3×103

1.4×10−19

3×104