Dual Nature of Light

Question 1

What are photons?

Answer 1

Photons are a stream of mass-less particles.

Question 2

What is electromagnetic radiation ?

Answer 2

It is an electric and magnetic disturbance traveling through space at the speed of light.

Question 3

Speed of light

Answer 3

3 x 10^8

Question 4

Electromagnetic radiation contains neither mass nor charge but travels in packet of energy called?

Answer 4

Photons

Question 5

EM radiation are classified by wavelengths into :

Answer 5

Radio waves, microwaves, infrared, ultraviolet, light , gamma and X-rays

Question 6

Photons consist of higher energy called

Answer 6

Quantum of radiation

Question 7

Who was the first to suggest that light is both a wave and a particle

Answer 7

Einstein and this is called wave-particle duality of light

Question 8

what is threshold frequency?

Answer 8

Threshold frequency is defined as the minimum frequency that is required for radiation such that photoelectric effect is produced.

Question 9

Which metals exhibit photoelectric effect?

Answer 9

Alkali metals are usually used for exhibiting photoelectric effect.
Metals such as copper and sodium are examples of metals that exhibit photoelectric effect.

Question 10

What type of light is needed to cause the photoelectric effect?

Answer 10

Ultraviolet light is the type of light that is needed to cause the photoelectric effect.

Question 11

What are the applications of photoelectric effect?

Answer 11

The applications of photoelectric effect are electric eye in door openers, light meters in photography, photostatic copying, and solar panels.

Question 12

explain the photoelectric effect

Answer 12

The photoelectric effect is a phenomenon where electrons are emitted from the metal surface when light of sufficient frequency is incident upon it.

Question 13

amount of energy in a photon is give by the equation:

Answer 13

E = mc^2 (Einstein); m=mass, c=speed of light (3 x 10^8ms-1)
Ephoton = hf (Planck) = mc^2 (f= frequency, h = planck’s constant as 6.626 x 10 ^-34 J.s)
E = hv
C = λ × v

Question 14

1nm =

Answer 14

1 x 10^-9

Question 15

1/λ = R(1/n1^2- 1/n2^2)

Answer 15

λ is the wavelength of the photon (1/wavelength = wavenumber )R = Rydberg’s constant (1.097 x 10^7m-1) n1 and n2are integers where n2> n1.
the Rydberg formula may be applied to hydrogen to obtain its spectral lines.

Question 16

Find the wavelength of theelectromagnetic radiation that is emitted from an electron that relaxes from n = 3 to n = 1.

Answer 16

1/λ = R(1/n12- 1/n22)
where n1is 1 and n2is 3.
Rydberg’s constant: 1.9074 x 107m-1
1/λ = (1.0974 x 107)(1/12- 1/32)1/λ = (1.0974 x 107)(1 - 1/9)1/λ = 9754666.67 m-11 = (9754666.67 m-1)λ1 / 9754666.67 m-1= λλ =
1.025 x 10-7m

Question 17

what is the law of multiple proportion?

Answer 17

law of multiple proportions states that when two elements form more than one compound, masses of one element that combine with a fixed mass of the other are in a ratio of small whole numbers.

Question 18

Rybergs constant

Answer 18

1.097 x 10^7

Question 19

planks constant (h)

Answer 19

6.626 x 10^-34 J/s