## Question

A 25 watt bulb emits monochromatic yellow light of wavelength of 0.57 μm. Calculate the rate of emission of quanta per second.

### Solution

Energy emitted by the bulb = 25 watt = 25 J s^{–1} (âˆµ 1 watt = 1 Js^{–1})

Energy of one photon (E) = *hv*

Hence,

∴ No. of photons emitted per sec

.

#### SIMILAR QUESTIONS

Calculate the uncertainty in the velocity of a wagon of mass 3000 kg whose position is known to an accuracy of ±10 pm

(Planck’s constant = 6.63 × 10^{–34} Js)

Calculate the uncertainty in the position of an electron if the uncertainty in its velocity is 5.7 × 10^{5} m/sec (*h* = 6.6 × 10^{–34} kg m^{2} s^{–1}, mass of the electron = 9.1×10^{–31} kg).

A golf ball has a mass of 40 *g* and a speed of 45 m/s. If the speed can be measured within accuracy of 2%, calculate the uncertainty in position.

If an electron is moving with a velocity 600 ms^{–1} which is accurate upto 0.005%, then calculate the uncertainty in its position.

(h = 6.63 × 10^{–34} Js, mass of electron = 9.1 × 10^{–31} kg)

What is the transition in the hydrogen spectrum would have the same wavelength as the Balmer transition, *n* = 4 to *n* = 2 of He^{+} spectrum?

Calculate the energy required for the process

He^{+} (*g*) → He^{2+} (*g*) + *e*^{–}

The ionization energy for the H atom in the ground state is

2.18 × 10^{–18} J atom^{–1}.

What is the wavelength of the light emitted when the electron in a hydrogen atom undergoes transition from an energy level with *n* = 4 to an energy level with *n* = 2? What is the colour corresponding to this wavelength? (Rydberg constant = 109,677 cm^{–1})

A certain particle carries 2.5 × 10^{–16} C of static electric charge. Calculate the number of electrons present in it.

An ion with mass number 37 possesses one unit of negative charge. If the ion contains 11.1% more neutrons then the electrons, find the symbol of the ion.

An ion with mass number 56 contains 3 units of positive charge and 30.4% more neutrons than electrons. Assign the symbol to this ion.