Pelajaran Fisika SMA kelas 11 gelombang.pptx

Slide pelajaran gelombang

1. WAVES

2. FUNDAMENTAL TYPES WAVE MOTION W ave is a disturbance that travels through space and matter, transferring energy from one place to another. The key idea is that wave motion transfers energy, not matter . Imagine a cork floating on water. As a wave passes, the cork moves up and down, but it returns to its original position. As a wave passes, the cork moves up and down, but it returns to its original position. The wave (the energy) moves across the water, but the water itself (the matter) only oscillates locally. Definition Types

3. Definition Types FUNDAMENTAL TYPES A transverse wave is a wave in which each particle of the medium moves perpendicular to the direction the wave travels . On a string, the wave moves along the string while the string elements move up–down; that’s transverse motion. Transverse Wave

4. FUNDAMENTAL TYPES A longitudinal wave is a wave in which particles of the medium oscillate parallel to the direction the wave travels . You can make one in a Slinky by repeatedly compressing and expanding one end: compressions and rarefactions move along the spring. Sound in air is a prime example. Longitudinal Wave Definition Types

5. DISPLACEMENT EQUATION A standard traveling sinusoidal wave can be written as :   W here , : Displacement from equilibrium : Position along the direction the wave travels : Time : Amplitude : Angular wavenumber : Angular frequency : Phase constant   Note: Negative (-) sign in front of , then the wave propagates to the right (+x) . Positive (+) sign in front of , then the wave propagates to the left (-x) . Positive (+) sign in front of A , then the particle starts moving upward . Negative (-) sign in front of A , then the particle starts moving downward .  

6. Wavelenght ( )   Distance over which the wave pattern repeats in space (crest to next crest). Phase ( )   How rapidly the phase changes with x   Angular Wavenumber ( )   How rapidly the phase changes with time. Unit: rad/s   Angular Frequency ( )   Wave Speed ( )   Wave speed is the speed at which the shape or disturbance of a wave travels through a medium.   Measure of the stage   Phase Angle ( )   measure of the stage of the cycle  

7. Velocity at a fixed position means the time derivative: Differentiate once more with respect to time:       When the point passes equilibrium ( ), is maximum At crests / troughs ( ), is minimum Don’t mix it up with wave speed!     PARTICLE VELOCITY & ACCELERATION EQUATION At crests / troughs ( ), is maximum and points back to the center When the point passes equilibrium ( ), is minimum  

8. EXERCISE Two boats, separated by 40 m, bob up and down with ocean waves. When one boat is at a crest, the other is at a trough, and two additional crests lie between them. Each boat completes 10 full up-and-down oscillations in 12 s. Determine: Period and frequency Wavelegth Wave speed

9. EXERCISE A wave is described by: Where y is in meters, t in seconds, and x in meters. Determine: Amplitude, frequency, period, wavelength, and the direction of propagation Wave speed   Points P and Q are located 1.0 m and 2.125 m from the wave source (at x = 0), respectively. At t = 20 s, determine: Phase angle (in radians), phase (in cycles), and displacement at point P; Phase angle, phase, displacement at point Q Phase difference between Q and P

10. EXERCISE A wave is described by: Point P is 1.0 m from the source. At t = 5 s, find the particle velocity and particle acceleration at P.  

11. WAVE PROPERTIES When a wave meets a boundary, part of its energy can reflect (go back) and part can transmit (go through). Frequency does not change at a boundary. The speed and wavelength may change if the wave enters a new medium, because .   Reflection Reflection Interferences On a rope or string Fixed end (clamped end) The reflected wave is inverted (a crest returns as a trough). That is a phase flip of π (half a cycle).

12. WAVE PROPERTIES When a wave meets a boundary, part of its energy can reflect (go back) and part can transmit (go through). Frequency does not change at a boundary. The speed and wavelength may change if the wave enters a new medium, because .   Reflection Reflection Interferences On a rope or string Free end (loose ring) The reflected wave is not inverted (crest returns as crest)

13. WAVE PROPERTIES Interferences Reflection Interferences When two or more waves overlap at the same place and time, the actual displacement is the sum of the individual displacements: If the sources have the same frequency (are coherent), the pattern is steady.  

14. WAVE PROPERTIES Interferences Reflection Interferences Constructive Interference (reinforcement) Destructive Interference (cancellation)

15. WAVE PROPERTIES Interferences Reflection Interferences

16. STANDING WAVE (STATIONARY WAVES) A standing wave is a vibration pattern that does not travel along the medium . Some points are always still (nodes), while others vibrate the most (antinodes) Standing waves form when two waves with the same frequency and amplitude move in opposite directions and interfere with each other —most often because a traveling wave reflects from a boundary. How it forms? Start with two opposite-direction waves on a string: Add them:  

17. STANDING WAVE (STATIONARY WAVES) Antinodes & Nodes From Antinode: maximum amplitude , when Nodes: Always zero when   Distances Between adjacent nodes = Between adjacent antinodes: : Between a node and its nearest antinode:  

18. STANDING WAVE (STATIONARY WAVES) Antinodes & Nodes From Antinode: maximum amplitude , when Nodes: Always zero when   Distances Between adjacent nodes = Between adjacent antinodes: : Between a node and its nearest antinode:  

19. STANDING WAVE (STATIONARY WAVES) Fixed End  

20. STANDING WAVE (STATIONARY WAVES) Free End  

21. EXERCISE A 116-cm string is stretched horizontally. One end is fixed, and the other end is driven sinusoidally with frequency 1/6 Hz and amplitude 10 cm. A traveling wave on the string has a speed of 8 cm/s. Determine: Equation of the standing wave that forms Oscillation amplitude of the string at a point 108 cm from the driver Position of the 3 rd antinode and the 4 th node, measured from the reflecting (fixed) end.