Question

A bulb emits light of wave length 1987.8/7 nm. The bulb is rated as 200w and 14%of the energy is emitting as light . How many photons are emitting by the bulb persecond​

Answer 1

Explanation:

Energy emitted per second by the bulb =150×

100

8

J

Energy of 1 photon =

λ

hc

=

4500×10

−10

6.626×10

−34

×3×10

8

=4.42×10

−19

joule

Let n photons be evolved per second.

∴n×4.42×10

−19

=150×

100

8

n=27.2×10

18

.

Answer 2

Answer:

4 x $10^{19}$ Quanta

Explanation:

λ = 1987.8/7 nm = 2.83 x $10^{-7}$ m (Converting into SI units)

200w = 200 J/s (Bulbs capacity to emit energy per second)

Condition : Only 14% of the energy is emitted as light

14% of 200 J/s = 200 x $\frac{14}{100}$ = 28 J/s = E

Now, we know that

Frequency, ν= c/λ = $\frac{3*10^{8} }{2.83*10^{-7} }$ = 1.06 x $10^{15}$

E=nhν

Hence, n = E/hν

               =$\frac{28}{6.626 * 10^{-34} * 1.06*10^{15} }$ = $\frac{28}{7*10^{-19} }$ = 4 x 10^19