Quantum theory

Question 1

explain how Young’s double-slit experiment provides evidence for the wave model of light

Answer 1

demonstrates the wave nature of light by allowing two coherent beams of light to overlap on a screen to form an interference pattern

Question 2

describe wave-particle duality of light

Answer 2

every particle or quantum entity may be partly described in terms not only of particles, but also waves

Question 3

explain wave-particle duality

Answer 3

in general if light energy is interacting with other forms of light energy, then the wave behaviour model is the best explanation. If light is interacting with matter, then the particles behaviour model is the best explanation

Question 4

define black body

Answer 4

an object that absorbs all radiation falling on it, at all wavelengths; it is a perfect absorber or emitter of radiation

Question 5

explain the concept of black body radiation

Answer 5

the radiation emitted by a black body from the conversion of thermal energy, and which has a characteristic frequency distribution that depends on temperature

Question 6

describe the concept of a photon

Answer 6

a quantum of all form of electromagnetic radiation

Question 7

describe the photoelectric effect in terms of the photon

Answer 7

when light above a certain energy shines on a material each photon collides with an electron and uses some its energy to emit the electron

Question 8

define the term threshold frequency

Answer 8

the minimum frequency of a photo that can eject an electron from a surface

Question 9

define Planck’s constant

Answer 9

a fundamental constant used in quantum mechanics that relates frequency to energy

Question 10

define work function

Answer 10

the minimum energy required to remove an electron from a solid

Question 11

describe Rutherford’s model of the atom

Answer 11

a small, central positively charged nucleus with negatively charged electrons orbiting around it

Question 12

what are the limitations of the Rutherford model

Answer 12

1. the failure to account for the stability of the atom
2. the failure to account for emission lines in the hydrogen spectrum

Question 13

describe the Bohr model of the atom

Answer 13

electrons orbit the nucleus in particular circular orbits called stationary states with fixed angular momentum and energy, their radius being proportional to their energy. When an electron moves between these stationary states, it is accomplished by the emission or absorption of a photon.

Question 14

how does the Bohr model address the Rutherford model

Answer 14

remedies the stability problem by requiring that the electrons move in orbits of fixed size and energy