Pulse
Wave Phenomena
Pulses & Periodic Waves
How individual disturbances travel, reflect, transmit, and repeat
What effect allows insects to walk on water?
Video Instruction
showmethephysics.com
B. Pulses & Periodic Waves
Animation created by User:Evil_saltine
Follow the Motion
In which direction will segment X move as the wave passes through it?
(1) Down only
(2) Up only
(3) Down, then up, then down
(4) Up, then down, then up
↓
Answer: (4) Up, then down, then up.
Reflection & Transmission
When light waves hit the surface of the bubble, two things happen. Name them.
Photo: Mila Zinkova; edited by Alvesgaspar
↓
Answer: Some light is transmitted and some is reflected.
When a pulse reaches a boundary with another medium, part of it is reflected and part is transmitted (goes through).
Reflection at a Fixed Boundary
Periodic Wave
Check Your Understanding
5 quick questions — pick an answer to see if you’re right.
1. A pulse is
2. A series of evenly timed disturbances in a medium is called a
3. A pulse on a rope reaches a boundary where it joins a different rope. What usually happens?
4. An upright pulse on a rope reaches a fixed, unyielding wall. The reflected pulse is
5. A pulse travels to the right along a horizontal rope. How do the pieces of rope themselves move?
Sending a Pulse Along a Rope
A student ties one end of a rope to a wall and flicks the free end once, sending a single upward pulse toward the wall. She then shakes the rope up and down continuously to make a periodic wave.
When the upward pulse reflects from the fixed end at the wall, what does the reflected pulse look like?
▶ Want a challenge? Open 6 more Regents-style questions (harder · mixed formats)
Challenge score: 0 / 6
Support or Refute · Justify
C1. A student makes the following claim.
Claim: If the student flicks the rope harder, making a pulse with a larger amplitude, the pulse will reach the wall in less time.
Place a check mark in either the Support or Refute box. Justify your response.
Multiple choice
C2. The light rope is tied to a much heavier rope instead of a wall. When a pulse reaches the boundary, what happens?
Substitute values
C3. The student shakes the rope at a steady 2.5 Hz. Waves travel along this rope at 15 m/s. Substitute numerical values into a mathematical representation that can be used to determine the wavelength of the periodic wave. Then calculate the wavelength.
λ = m/s Hz = m
Draw the vector · Determine the magnitude
C4. The student stands to the left of the wall. Her upward pulse travels the 6.0-m length of the rope to the wall in 0.40 s. After the pulse reflects from the wall, choose the direction of the reflected pulse’s velocity, and determine its magnitude.
reflected pulse
●
●
v = m/s
Multiple choice
C5. The free end of a rope is attached to a ring that slides freely on a pole. How does a pulse reflect?
Constructed response
C6. Just after the first pulse reflects (inverted) from the wall, the student sends a second upward pulse of the same size toward the wall. Describe what happens when the two pulses meet, and describe the pulses after they pass each other.
