Progressive waves introduction

what is a progressive wave?

• an oscillation that travels through matter (sometimes through a vacuum)

• transfers energy but not matter

• the particles in the medium move from their original equilibrium position to a new position

• a displaced particle experiences a restoring force from its neighbours so it is pulled back to its original position

transverse waves

• oscillations are perpendicular to direction of energy transfer

• peaks and troughs: where the oscillating particles are at maximum displacement from their equilibrium

longitudinal waves

• the oscillations are parallel to the direction of energy transfer

• when they travel through a medium they create a series of compressions and rarefactions

• when sound waves travel through air, the air particles are displaced and bounce off their neighbours. these collisions provide the restoring force

displacement

distance from the equilibrium position in a particular direction (it’s a vector)

amplitude

maximum displacement from the equilibrium position

wavelength

minimum distance between two points in phase on adjacent waves

period of oscillation

the time taken for one oscillation or time taken for wave to move one whole wavelength past a given point

frequency

the number of wavelengths passing a given point per unit time

wavespeed

the distance travelled by the wave per unit time

what is phase difference?

• ocr mark scheme definition: difference in degrees/radians between two points on the same wave or similar points on two waves

• oxford revise definition: the fraction of a cycle by which two points oscillations are separated, measured in radians

how to conver between degrees and radians?

multiply degrees by (pi/180) to get radians

what does being in phase mean?

when particles are oscillating perfectly in step with each other and their phase difference is 0

what does being in antiphase mean?

when particles are oscillating completely out of step with each other, eg one reaches its maximum positive displacement at the same time as the other reaches its maximum negative displacement, their phase difference is 180

what is the equation for phase difference

phase difference= (distance between two points / wavelength) * 360