Turning Points- Wave-Particle duality Flashcards
What was Newton’s corpuscular theory?
Newton’s theory that light exists as discrete packets
called corpuscles that travel in straight lines and have momentum
How did Newton’s corpuscular theory explain reflection?
Corpuscles collide with surface and experience repulsive force perpendicular to surface so component of velocity perpendicular to surface changes and component parallel stays the same
How did Newton’s corpuscular theory explain refraction?
Corpuscles approach optically denser medium and experience short-range attractive forces causing velocity component perpendicular to surface to increase while parallel component stays the same so light bends towards the normal.
This means light travels faster in denser mediums
What was Huygens’ wave theory of light?
Huygens’ theory that light was a wave and every point on a wavefront is a point source to secondary wavelets which spread to form the next wavefront (Huygens’ principle)
How did Huygens’ wave theory explain reflection?
The wavefront reaches the boundary at different times (unless moving perpendicular to it) and wavelets spread away from the surface forming reflected wavefront
How did Huygens’ wave theory explain refraction?
Assumed that light travels SLOWER in an optically denser medium, therefore slower wavelets are produced and form a wavefront closer to the normal
Why was Newton’s theory accepted over Huygens’?
-Newton had a very high reputation at the time
-Diffraction could not be explained by Newton however it had not yet been observed
-Speed of light hadn’t yet been measured and compared in optically denser mediums
What is Young’s double slit experiment?
Coherent light shone through two slits, each acting as a coherent point source. The light interferes producing bright and dark fringes, constructively where they meet in phase and destructively where they meet in antiphase
What was the significance of Young’s double slit experiment?
Proved wave nature of light as corpuscular theory predicted two bright fringes but interference pattern demonstrated diffraction and interference, both wave properties. This led to Huygens’ wave theory of light being accepted. Newton’s theory disregarded after light was found to be slower in water
What are electromagnetic waves?
Transverse waves formed of alternating magnetic and electric fields travelling in phase and at right angles to each other. Direction of wave travel is perpendicular to direction of oscillations
What did Maxwell predict?
The existence of EM waves and made an equation predicting their speed in a vacuum, c = 1/√μoεo
What is μo?
The permeability of free space, relating magnetic flux density produced by a wire to the current in the wire
What is εo?
The permittivity of free space, relating electric field strength to the charge on the object which formed the field
How did Hertz discover radio waves?
Used apparatus which allow high voltage sparks to jump across a gap of air and be detected using a receiver.
Spark gap transmitter produced a spark, receiver was a loop of wire with a gap, detects wave’s alternative magnetic field causing flux cutting, inducing a pd across the gap causing a spark across it
How did Hertz measure the speed of light?
By placing a metal sheet in front of the spark transmitter, stationary waves are formed. Using the loop of wire, distance between adjacent nodes and antinodes can be measured (no spark or spark) to calculate wavelength. Using frequency of the waves, speed can be found and it confirmed Maxwell’s predictions
How did Fizeau measure the speed of light?
Pulsing light
