Chapter 10 light wave model

Question 1

What did Isaac Newton believe about the nature of light?

Answer 1

He described light as particles (‘corpuscles’), with each colour being a different type of particle.

Question 2

What did Christiaan Huygens believe about light?

Answer 2

He described light as a wave, similar to water waves.

Question 3

How did Newton’s and Huygens’ theories differ about light in glass?

Answer 3

Newton’s corpuscular theory predicted light would speed up in glass; Huygens’ wave theory predicted it would slow down.

Question 4

What does Huygens’ Principle state?

Answer 4

Each point on a wavefront acts as a source of secondary wavelets, which combine to form the new wavefront.

Question 5

What properties of light can only be explained using the wave model?

Answer 5

Diffraction, interference, and polarisation.

Question 6

What is diffraction?

Answer 6

The bending of waves around obstacles or through narrow openings.

Question 7

When is diffraction most significant?

Answer 7

When the opening or obstacle is similar to or smaller than the wavelength of the wave.

Question 8

Why is diffraction of light difficult to observe in nature?

Answer 8

Because visible light wavelengths (400–700 nm) are very small, so natural objects are usually too large.

Question 9

How can diffraction of light be seen artificially?

Answer 9

Using CDs, DVDs, or diffraction gratings.

Question 10

What determines the extent of diffraction?

Answer 10

The ratio λ / w, where λ is the wavelength and w is the slit width.

Question 11

What is a diffraction pattern?

Answer 11

A series of bright and dark bands formed by constructive and destructive interference of diffracted waves.

Question 12

Which colour diffracts more: red or blue light? Why?

Answer 12

Red light, because it has a longer wavelength.

Question 13

What is a diffraction grating?

Answer 13

A material with many closely spaced slits that produces strong, clear interference patterns.

we used these in our experiments

Question 14

What did Thomas Young’s experiment (1803) demonstrate?

Double slit experiment

Answer 14

That light produces an interference pattern, supporting the wave model.

very importnant

Question 15

According to the particle theory, what pattern should have appeared in Young’s experiment?

Answer 15

Two bright bands directly behind the slits.

Question 16

What did Young actually observe?

Answer 16

A series of bright and dark fringes caused by constructive and destructive interference.

Question 17

When does constructive interference occur?

Answer 17

When the path difference equals a whole number of wavelengths (pd = mλ).

Question 18

When does destructive interference occur?

Answer 18

When the path difference equals an odd number of half-wavelengths (pd = (m+½)λ).

Question 19

What is the central maximum in Young’s experiment?

Answer 19

The bright central fringe where the path difference is zero.

Question 20

What is the formula for bright fringes in Young’s double-slit experiment?

Answer 20

d sinθ = mλ, where d = slit separation, θ = angle, m = order of fringe.