Physics: Waves, Sound and Light

False. Sound is a mechanical wave and needs a medium (solid, liquid or gas) to carry its vibrations. Light, an electromagnetic wave, does travel through a vacuum, which is why we see the Sun but cannot hear it.

, so . 1.28 comes from dividing f by v, and 151,000 multiplies them.

. Period and frequency are reciprocals.

Air molecules vibrate back and forth along the direction the wave travels, forming compressions and rarefactions. Light and waves on a string are transverse.

Higher frequency means higher pitch. Amplitude controls loudness (energy), not pitch.

. Forgetting to convert nm to m gives .

Frequency (and photon energy) rises from radio to gamma, while wavelength falls. The reverse list is the order of increasing wavelength.

The Doppler effect: waves bunch up in front of a moving source, so you receive a higher frequency. As it moves away, the waves spread out and the pitch drops.

Glass has a higher refractive index than air, so light slows down, and Snell's law says the angle to the normal gets smaller. Going from glass back into air, it bends away from the normal.

: , so and . An angle larger than 30° would mean bending away from the normal, which is wrong for air to glass.

Only when light heads into a slower-to-faster boundary (like glass to air) can the refracted angle reach 90°. Beyond the critical angle, all the light reflects. This is how optical fibers trap light.

Whole-wavelength path differences bring crests together with crests, so the amplitudes add. Half-wavelength differences (λ/2, 3λ/2, ...) give destructive interference.

For a string fixed at both ends, the fundamental wavelength is . . 200 Hz wrongly uses .

. Light can never go faster than c, so is impossible.

Frequency is set by the source, so it does not change at a boundary. Speed changes with the medium, and since , the wavelength changes too.

Thin-lens equation: , so and . The image is real, inverted and half the object's size (magnification = −15/30).