Pulse - definition A pulse is simply a wave of short duration Examples would be a short burst of sound like beeps, or a string being waved up and down once then stopped Pulses travel on or in their medium until they reach a boundary velocity of wave single wave part moving along the string

Wave behaviour We already know about some kinds of transmission and reflection and can describe it using simple ideas In this section, we’re interested in wave pulses moving from one medium to another across a boundary At this level, we concentrate on waves on strings moving between a heavy string and a light string or vice versa

Transmission and reflection Transmission is when part or all of the wave passes through a boundary Reflection is when part or all of the wave bounces back from the boundary In the case of a wave pulse on a spring, some of the wave is transmitted and some is reflected

Heavy string to light string What do you notice about the amplitude, direction, speed of motion and orientation of the pulses?

Heavy string to light string The transmitted pulse is upright It has a lower amplitude It moves faster than the incident pulse, so is further from the boundary The reflected pulse is upright It has a smaller amplitude It moves at the same speed as the incident pulse, so is closer to the boundary

Light string to heavy string What do you notice about the amplitude, direction, speed of motion and orientation of the pulses?

Light string to heavy string The transmitted pulse is upright It has a lower amplitude It moves slower than the incident pulse, so is closer to the boundary The reflected pulse is inverted It has a smaller amplitude It moves at the same speed as the incident pulse, so is further from the boundary

Why is the amplitude smaller? The wave pulses change energy from one form to another when they reflect and transmit Because the waves have less energy, the amplitude is smaller

A sample question A wave pulse is observed to move from one string to another across a boundary. It moves faster in the second string than the first. Sketch a diagram to show what the pulse will look like after hitting the boundary

Solution First, decide if this is a light-to-heavy string or heavy-to- light string problem Since we’re told the wave pulse moves faster in the second string, and we know that the speed of a wave on a string is faster for lighter strings, this must be a heavy-to- light string problem Decide how your reflected and transmitted pulses will look, using the information from earlier

Solution Make sure you have met all the criteria for both wave pulses – for a heavy string to a light string they should both be upright both have smaller amplitude than the original pulse the reflected wave closer to the boundary velocity of reflected wave Velocity of transmitted wave