What is the number of photons emitted per second by a 100-watt bulb, when it emits monochromatic light of wavelength 400 nm?
1. \(40.12 \times 10^{20} \ s^{-1}\)
2. \(2.012 \times 10^{21} \ s^{-1}\)
3. \(2.012 \times 10^{20} \ s^{-1}\)
4. \(20.12 \times 10^{21} \ s^{-1}\)

When electromagnetic radiation of wavelength 300 nm falls on the surface of sodium, electrons are emitted with a kinetic energy of 1.68 ×10⁵ J mol^–1. The minimum energy needed to remove an electron from sodium and the maximum wavelength that will cause a photoelectron to be emitted are, respectively:

1. 2.31 × 10⁵ J mol^–1, 517 nm

2. 23.1 × 10⁵ J mol^–1, 517 nm

3. 3.31 × 10⁵ J mol^–1, 417 nm

4. 33.1 × 10⁵ J mol^–1, 417 nm

The threshold frequency ν_o for a metal is 7.0 ×10¹⁴ s^–1. The kinetic energy of an electron emitted when radiation of frequency ν =1.0 ×10¹⁵ s^–1 hits the metal, is-

1. 19.88 ×10^–19 J

2. 1.988 ×10^–19 J

3. 1.988 ×10^–20 J

4. 19.88 ×10^–17 J