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THINGS YOU NEED TO KNOW For Regents Physics Exam
Waves
4.3a-
Mechanical waves-Travel through matter-solid liquid gas. Example sound, water ripples, slinky
Electromagnetic waves-Light
4.3b-Waves carry energy only
Amplitude of wave is representative of Energy. Amplitude for sound=loudness…for light=brightness.
Wave Pulse-one “bump” wave OR single vibratory disturbance
Periodic Wave-Repeating wave
4.3c- Wave anatomy: Know
Wavelength from a diagram (2 “bumps” = one wavelength)
Frequency is the number of repetitions (or cycles) per time. Period is time per repetition.
Frequency= inverse of Period…
Period= inverse of frequency.
Amplitude shows amount of Energy
Wave speed is always constant in same medium
Points are “In phase” on a periodic wave if amplitude and motion (up-down) are the same.
4.3d- Sound waves travel in air at 330 m/s (RRT-Constants) Sound travels faster in water and solids.
Radio waves are NOT sound waves (common misconception)
Sound waves are mechanical waves
4.3eTRANVERSE WAVES- particles in medium vibrate perpendicular to motion of wave (string, light)
LONGITUDINAL WAVES- medium vibrate along direction on motion of wave. (sound waves)
4.3fSTANDING WAVES-Waves that are results of a wave and it reflection, causing INTERFERENCE
RESONANCE is when one object starts to vibrate at its natural frequency due to another vibration
of the same frequency. All objects/air chambers RESONATE at their own NATURAL FREQUENCY.
The resonant waves are STANDING WAVES.
NODES-Points on a standing wave of complete DESTRUCTIVE INTERFERENCE (180° out of phase)
ANTI NODES-Points on a standing wave of complete CONSTRUCTIVE INTERFERENCE (in phase)
2 “bumps” of a standing wave (or any wave) is equal to one wavelength.
4.3gElectromagnetic Waves (Light) can travel through a vacuum.
Electromagnetic waves are transverse waves
4.3hWaves (Light or Sound) going from one medium to another will either
REFLECT-bounce back, same speed, same angle, same freq and wavelength,
REFRACT(Transmit)-continue at different speed, wavelength, and angle… BUT SAME FREQ
Be ABSORBED-wave energy is absorbed by medium and increases its temperature.
4.3ILight rays that go from a LOWER index of refraction to HIGHER, will bend TOWARDS the normal,
will decrease in speed and have shorter wavelengths. (Still the same frequency)
Light rays that go from a HIGHER index of refraction to LOWER, will bend AWAY from the normal,
Will increase in speed and have longer wavelengths. (Still the same frequency)
The NORMAL is a line drawn perpendicular to the surface between mediums.
4.3jThe index of refraction is always greater than (or equal to) 1.00
The speed of light in any medium IS ALWAYS less than c.
4.3kThe speed of light in a vacuum is the same for all types of light, which is = c.
4.3lDIFFRACTION is the bending of waves around a barrier (or spreading out circularly from a slit)
Diffraction is only a noticeable phenomenon when the wavelength is close to the size of the slit.
4.3m- PRINCIPLE OF SUPERPOSITION (ADDING AMPLITUDES) is the idea behind ANY type of interference:
STANDING WAVES, CONSTRUCTIVE INTERFERENCE, and DESTRUCTIVE INTERFERENCE.
CONSTRUCTIVE INTERFERENCE- When two waves that are IN PHASE with each other are at the
same point in the medium. The result is maximum amplitude. (2 crests or 2 troughs)
DESTRUCTIVE INTERFERENCE- When two waves are 180° OUT OF PHASE WITH EACH OTHER.
This results at a NODE point and there is NO amplitude to the wave-(Dark or quiet spot.)
4.3nDoppler Effect- When the wave source (siren, flashlight) is
MOVING TOWARDS listener: SHORTER WAVELENGTH, HIGHER FREQUENCY
MOVING AWAY FROM listener: LONGER WAVELENGTH, LOWER FREQUENCY
If light is the wave, then moving towards is called BLUESHIFT, and away is REDSHIFT.